Merge "Move all of the reasonable DatabaseBase methods to Database class"

[lhc/web/wiklou.git] / includes / libs / rdbms / database / IDatabase.php

<?php

/**
 * @defgroup Database Database
 *
 * This file deals with database interface functions
 * and query specifics/optimisations.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 * @ingroup Database
 */

/**
 * Basic database interface for live and lazy-loaded DB handles
 *
 * @note: IDatabase and DBConnRef should be updated to reflect any changes
 * @ingroup Database
 */
interface IDatabase {
        /** @var int Callback triggered immediately due to no active transaction */
        const TRIGGER_IDLE = 1;
        /** @var int Callback triggered by COMMIT */
        const TRIGGER_COMMIT = 2;
        /** @var int Callback triggered by ROLLBACK */
        const TRIGGER_ROLLBACK = 3;

        /** @var string Transaction is requested by regular caller outside of the DB layer */
        const TRANSACTION_EXPLICIT = '';
        /** @var string Transaction is requested internally via DBO_TRX/startAtomic() */
        const TRANSACTION_INTERNAL = 'implicit';

        /** @var string Transaction operation comes from service managing all DBs */
        const FLUSHING_ALL_PEERS = 'flush';
        /** @var string Transaction operation comes from the database class internally */
        const FLUSHING_INTERNAL = 'flush';

        /** @var string Do not remember the prior flags */
        const REMEMBER_NOTHING = '';
        /** @var string Remember the prior flags */
        const REMEMBER_PRIOR = 'remember';
        /** @var string Restore to the prior flag state */
        const RESTORE_PRIOR = 'prior';
        /** @var string Restore to the initial flag state */
        const RESTORE_INITIAL = 'initial';

        /** @var string Estimate total time (RTT, scanning, waiting on locks, applying) */
        const ESTIMATE_TOTAL = 'total';
        /** @var string Estimate time to apply (scanning, applying) */
        const ESTIMATE_DB_APPLY = 'apply';

        /**
         * A string describing the current software version, and possibly
         * other details in a user-friendly way. Will be listed on Special:Version, etc.
         * Use getServerVersion() to get machine-friendly information.
         *
         * @return string Version information from the database server
         */
        public function getServerInfo();

        /**
         * Turns buffering of SQL result sets on (true) or off (false). Default is
         * "on".
         *
         * Unbuffered queries are very troublesome in MySQL:
         *
         *   - If another query is executed while the first query is being read
         *     out, the first query is killed. This means you can't call normal
         *     MediaWiki functions while you are reading an unbuffered query result
         *     from a normal wfGetDB() connection.
         *
         *   - Unbuffered queries cause the MySQL server to use large amounts of
         *     memory and to hold broad locks which block other queries.
         *
         * If you want to limit client-side memory, it's almost always better to
         * split up queries into batches using a LIMIT clause than to switch off
         * buffering.
         *
         * @param null|bool $buffer
         * @return null|bool The previous value of the flag
         */
        public function bufferResults( $buffer = null );

        /**
         * Gets the current transaction level.
         *
         * Historically, transactions were allowed to be "nested". This is no
         * longer supported, so this function really only returns a boolean.
         *
         * @return int The previous value
         */
        public function trxLevel();

        /**
         * Get the UNIX timestamp of the time that the transaction was established
         *
         * This can be used to reason about the staleness of SELECT data
         * in REPEATABLE-READ transaction isolation level.
         *
         * @return float|null Returns null if there is not active transaction
         * @since 1.25
         */
        public function trxTimestamp();

        /**
         * @return bool Whether an explicit transaction or atomic sections are still open
         * @since 1.28
         */
        public function explicitTrxActive();

        /**
         * Get/set the table prefix.
         * @param string $prefix The table prefix to set, or omitted to leave it unchanged.
         * @return string The previous table prefix.
         */
        public function tablePrefix( $prefix = null );

        /**
         * Get/set the db schema.
         * @param string $schema The database schema to set, or omitted to leave it unchanged.
         * @return string The previous db schema.
         */
        public function dbSchema( $schema = null );

        /**
         * Get properties passed down from the server info array of the load
         * balancer.
         *
         * @param string $name The entry of the info array to get, or null to get the
         *   whole array
         *
         * @return array|mixed|null
         */
        public function getLBInfo( $name = null );

        /**
         * Set the LB info array, or a member of it. If called with one parameter,
         * the LB info array is set to that parameter. If it is called with two
         * parameters, the member with the given name is set to the given value.
         *
         * @param string $name
         * @param array $value
         */
        public function setLBInfo( $name, $value = null );

        /**
         * Set a lazy-connecting DB handle to the master DB (for replication status purposes)
         *
         * @param IDatabase $conn
         * @since 1.27
         */
        public function setLazyMasterHandle( IDatabase $conn );

        /**
         * Returns true if this database does an implicit sort when doing GROUP BY
         *
         * @return bool
         */
        public function implicitGroupby();

        /**
         * Returns true if this database does an implicit order by when the column has an index
         * For example: SELECT page_title FROM page LIMIT 1
         *
         * @return bool
         */
        public function implicitOrderby();

        /**
         * Return the last query that went through IDatabase::query()
         * @return string
         */
        public function lastQuery();

        /**
         * Returns true if the connection may have been used for write queries.
         * Should return true if unsure.
         *
         * @return bool
         */
        public function doneWrites();

        /**
         * Returns the last time the connection may have been used for write queries.
         * Should return a timestamp if unsure.
         *
         * @return int|float UNIX timestamp or false
         * @since 1.24
         */
        public function lastDoneWrites();

        /**
         * @return bool Whether there is a transaction open with possible write queries
         * @since 1.27
         */
        public function writesPending();

        /**
         * Returns true if there is a transaction open with possible write
         * queries or transaction pre-commit/idle callbacks waiting on it to finish.
         * This does *not* count recurring callbacks, e.g. from setTransactionListener().
         *
         * @return bool
         */
        public function writesOrCallbacksPending();

        /**
         * Get the time spend running write queries for this transaction
         *
         * High times could be due to scanning, updates, locking, and such
         *
         * @param string $type IDatabase::ESTIMATE_* constant [default: ESTIMATE_ALL]
         * @return float|bool Returns false if not transaction is active
         * @since 1.26
         */
        public function pendingWriteQueryDuration( $type = self::ESTIMATE_TOTAL );

        /**
         * Get the list of method names that did write queries for this transaction
         *
         * @return array
         * @since 1.27
         */
        public function pendingWriteCallers();

        /**
         * Is a connection to the database open?
         * @return bool
         */
        public function isOpen();

        /**
         * Set a flag for this connection
         *
         * @param int $flag DBO_* constants from Defines.php:
         *   - DBO_DEBUG: output some debug info (same as debug())
         *   - DBO_NOBUFFER: don't buffer results (inverse of bufferResults())
         *   - DBO_TRX: automatically start transactions
         *   - DBO_DEFAULT: automatically sets DBO_TRX if not in command line mode
         *       and removes it in command line mode
         *   - DBO_PERSISTENT: use persistant database connection
         * @param string $remember IDatabase::REMEMBER_* constant [default: REMEMBER_NOTHING]
         */
        public function setFlag( $flag, $remember = self::REMEMBER_NOTHING );

        /**
         * Clear a flag for this connection
         *
         * @param int $flag DBO_* constants from Defines.php:
         *   - DBO_DEBUG: output some debug info (same as debug())
         *   - DBO_NOBUFFER: don't buffer results (inverse of bufferResults())
         *   - DBO_TRX: automatically start transactions
         *   - DBO_DEFAULT: automatically sets DBO_TRX if not in command line mode
         *       and removes it in command line mode
         *   - DBO_PERSISTENT: use persistant database connection
         * @param string $remember IDatabase::REMEMBER_* constant [default: REMEMBER_NOTHING]
         */
        public function clearFlag( $flag, $remember = self::REMEMBER_NOTHING );

        /**
         * Restore the flags to their prior state before the last setFlag/clearFlag call
         *
         * @param string $state IDatabase::RESTORE_* constant. [default: RESTORE_PRIOR]
         * @since 1.28
         */
        public function restoreFlags( $state = self::RESTORE_PRIOR );

        /**
         * Returns a boolean whether the flag $flag is set for this connection
         *
         * @param int $flag DBO_* constants from Defines.php:
         *   - DBO_DEBUG: output some debug info (same as debug())
         *   - DBO_NOBUFFER: don't buffer results (inverse of bufferResults())
         *   - DBO_TRX: automatically start transactions
         *   - DBO_PERSISTENT: use persistant database connection
         * @return bool
         */
        public function getFlag( $flag );

        /**
         * General read-only accessor
         *
         * @param string $name
         * @return string
         */
        public function getProperty( $name );

        /**
         * @return string
         */
        public function getDomainID();

        /**
         * Alias for getDomainID()
         *
         * @return string
         */
        public function getWikiID();

        /**
         * Get the type of the DBMS, as it appears in $wgDBtype.
         *
         * @return string
         */
        public function getType();

        /**
         * Open a connection to the database. Usually aborts on failure
         *
         * @param string $server Database server host
         * @param string $user Database user name
         * @param string $password Database user password
         * @param string $dbName Database name
         * @return bool
         * @throws DBConnectionError
         */
        public function open( $server, $user, $password, $dbName );

        /**
         * Fetch the next row from the given result object, in object form.
         * Fields can be retrieved with $row->fieldname, with fields acting like
         * member variables.
         * If no more rows are available, false is returned.
         *
         * @param ResultWrapper|stdClass $res Object as returned from IDatabase::query(), etc.
         * @return stdClass|bool
         * @throws DBUnexpectedError Thrown if the database returns an error
         */
        public function fetchObject( $res );

        /**
         * Fetch the next row from the given result object, in associative array
         * form. Fields are retrieved with $row['fieldname'].
         * If no more rows are available, false is returned.
         *
         * @param ResultWrapper $res Result object as returned from IDatabase::query(), etc.
         * @return array|bool
         * @throws DBUnexpectedError Thrown if the database returns an error
         */
        public function fetchRow( $res );

        /**
         * Get the number of rows in a result object
         *
         * @param mixed $res A SQL result
         * @return int
         */
        public function numRows( $res );

        /**
         * Get the number of fields in a result object
         * @see http://www.php.net/mysql_num_fields
         *
         * @param mixed $res A SQL result
         * @return int
         */
        public function numFields( $res );

        /**
         * Get a field name in a result object
         * @see http://www.php.net/mysql_field_name
         *
         * @param mixed $res A SQL result
         * @param int $n
         * @return string
         */
        public function fieldName( $res, $n );

        /**
         * Get the inserted value of an auto-increment row
         *
         * The value inserted should be fetched from nextSequenceValue()
         *
         * Example:
         * $id = $dbw->nextSequenceValue( 'page_page_id_seq' );
         * $dbw->insert( 'page', [ 'page_id' => $id ] );
         * $id = $dbw->insertId();
         *
         * @return int
         */
        public function insertId();

        /**
         * Change the position of the cursor in a result object
         * @see http://www.php.net/mysql_data_seek
         *
         * @param mixed $res A SQL result
         * @param int $row
         */
        public function dataSeek( $res, $row );

        /**
         * Get the last error number
         * @see http://www.php.net/mysql_errno
         *
         * @return int
         */
        public function lastErrno();

        /**
         * Get a description of the last error
         * @see http://www.php.net/mysql_error
         *
         * @return string
         */
        public function lastError();

        /**
         * mysql_fetch_field() wrapper
         * Returns false if the field doesn't exist
         *
         * @param string $table Table name
         * @param string $field Field name
         *
         * @return Field
         */
        public function fieldInfo( $table, $field );

        /**
         * Get the number of rows affected by the last write query
         * @see http://www.php.net/mysql_affected_rows
         *
         * @return int
         */
        public function affectedRows();

        /**
         * Returns a wikitext link to the DB's website, e.g.,
         *   return "[http://www.mysql.com/ MySQL]";
         * Should at least contain plain text, if for some reason
         * your database has no website.
         *
         * @return string Wikitext of a link to the server software's web site
         */
        public function getSoftwareLink();

        /**
         * A string describing the current software version, like from
         * mysql_get_server_info().
         *
         * @return string Version information from the database server.
         */
        public function getServerVersion();

        /**
         * Closes a database connection.
         * if it is open : commits any open transactions
         *
         * @throws DBError
         * @return bool Operation success. true if already closed.
         */
        public function close();

        /**
         * @param string $error Fallback error message, used if none is given by DB
         * @throws DBConnectionError
         */
        public function reportConnectionError( $error = 'Unknown error' );

        /**
         * Run an SQL query and return the result. Normally throws a DBQueryError
         * on failure. If errors are ignored, returns false instead.
         *
         * In new code, the query wrappers select(), insert(), update(), delete(),
         * etc. should be used where possible, since they give much better DBMS
         * independence and automatically quote or validate user input in a variety
         * of contexts. This function is generally only useful for queries which are
         * explicitly DBMS-dependent and are unsupported by the query wrappers, such
         * as CREATE TABLE.
         *
         * However, the query wrappers themselves should call this function.
         *
         * @param string $sql SQL query
         * @param string $fname Name of the calling function, for profiling/SHOW PROCESSLIST
         *     comment (you can use __METHOD__ or add some extra info)
         * @param bool $tempIgnore Whether to avoid throwing an exception on errors...
         *     maybe best to catch the exception instead?
         * @throws DBError
         * @return bool|ResultWrapper True for a successful write query, ResultWrapper object
         *     for a successful read query, or false on failure if $tempIgnore set
         */
        public function query( $sql, $fname = __METHOD__, $tempIgnore = false );

        /**
         * Report a query error. Log the error, and if neither the object ignore
         * flag nor the $tempIgnore flag is set, throw a DBQueryError.
         *
         * @param string $error
         * @param int $errno
         * @param string $sql
         * @param string $fname
         * @param bool $tempIgnore
         * @throws DBQueryError
         */
        public function reportQueryError( $error, $errno, $sql, $fname, $tempIgnore = false );

        /**
         * Free a result object returned by query() or select(). It's usually not
         * necessary to call this, just use unset() or let the variable holding
         * the result object go out of scope.
         *
         * @param mixed $res A SQL result
         */
        public function freeResult( $res );

        /**
         * A SELECT wrapper which returns a single field from a single result row.
         *
         * Usually throws a DBQueryError on failure. If errors are explicitly
         * ignored, returns false on failure.
         *
         * If no result rows are returned from the query, false is returned.
         *
         * @param string|array $table Table name. See IDatabase::select() for details.
         * @param string $var The field name to select. This must be a valid SQL
         *   fragment: do not use unvalidated user input.
         * @param string|array $cond The condition array. See IDatabase::select() for details.
         * @param string $fname The function name of the caller.
         * @param string|array $options The query options. See IDatabase::select() for details.
         *
         * @return bool|mixed The value from the field, or false on failure.
         */
        public function selectField(
                $table, $var, $cond = '', $fname = __METHOD__, $options = []
        );

        /**
         * A SELECT wrapper which returns a list of single field values from result rows.
         *
         * Usually throws a DBQueryError on failure. If errors are explicitly
         * ignored, returns false on failure.
         *
         * If no result rows are returned from the query, false is returned.
         *
         * @param string|array $table Table name. See IDatabase::select() for details.
         * @param string $var The field name to select. This must be a valid SQL
         *   fragment: do not use unvalidated user input.
         * @param string|array $cond The condition array. See IDatabase::select() for details.
         * @param string $fname The function name of the caller.
         * @param string|array $options The query options. See IDatabase::select() for details.
         *
         * @return bool|array The values from the field, or false on failure
         * @since 1.25
         */
        public function selectFieldValues(
                $table, $var, $cond = '', $fname = __METHOD__, $options = []
        );

        /**
         * Execute a SELECT query constructed using the various parameters provided.
         * See below for full details of the parameters.
         *
         * @param string|array $table Table name
         * @param string|array $vars Field names
         * @param string|array $conds Conditions
         * @param string $fname Caller function name
         * @param array $options Query options
         * @param array $join_conds Join conditions
         *
         *
         * @param string|array $table
         *
         * May be either an array of table names, or a single string holding a table
         * name. If an array is given, table aliases can be specified, for example:
         *
         *    [ 'a' => 'user' ]
         *
         * This includes the user table in the query, with the alias "a" available
         * for use in field names (e.g. a.user_name).
         *
         * All of the table names given here are automatically run through
         * DatabaseBase::tableName(), which causes the table prefix (if any) to be
         * added, and various other table name mappings to be performed.
         *
         * Do not use untrusted user input as a table name. Alias names should
         * not have characters outside of the Basic multilingual plane.
         *
         * @param string|array $vars
         *
         * May be either a field name or an array of field names. The field names
         * can be complete fragments of SQL, for direct inclusion into the SELECT
         * query. If an array is given, field aliases can be specified, for example:
         *
         *   [ 'maxrev' => 'MAX(rev_id)' ]
         *
         * This includes an expression with the alias "maxrev" in the query.
         *
         * If an expression is given, care must be taken to ensure that it is
         * DBMS-independent.
         *
         * Untrusted user input must not be passed to this parameter.
         *
         * @param string|array $conds
         *
         * May be either a string containing a single condition, or an array of
         * conditions. If an array is given, the conditions constructed from each
         * element are combined with AND.
         *
         * Array elements may take one of two forms:
         *
         *   - Elements with a numeric key are interpreted as raw SQL fragments.
         *   - Elements with a string key are interpreted as equality conditions,
         *     where the key is the field name.
         *     - If the value of such an array element is a scalar (such as a
         *       string), it will be treated as data and thus quoted appropriately.
         *       If it is null, an IS NULL clause will be added.
         *     - If the value is an array, an IN (...) clause will be constructed
         *       from its non-null elements, and an IS NULL clause will be added
         *       if null is present, such that the field may match any of the
         *       elements in the array. The non-null elements will be quoted.
         *
         * Note that expressions are often DBMS-dependent in their syntax.
         * DBMS-independent wrappers are provided for constructing several types of
         * expression commonly used in condition queries. See:
         *    - IDatabase::buildLike()
         *    - IDatabase::conditional()
         *
         * Untrusted user input is safe in the values of string keys, however untrusted
         * input must not be used in the array key names or in the values of numeric keys.
         * Escaping of untrusted input used in values of numeric keys should be done via
         * IDatabase::addQuotes()
         *
         * @param string|array $options
         *
         * Optional: Array of query options. Boolean options are specified by
         * including them in the array as a string value with a numeric key, for
         * example:
         *
         *    [ 'FOR UPDATE' ]
         *
         * The supported options are:
         *
         *   - OFFSET: Skip this many rows at the start of the result set. OFFSET
         *     with LIMIT can theoretically be used for paging through a result set,
         *     but this is discouraged in MediaWiki for performance reasons.
         *
         *   - LIMIT: Integer: return at most this many rows. The rows are sorted
         *     and then the first rows are taken until the limit is reached. LIMIT
         *     is applied to a result set after OFFSET.
         *
         *   - FOR UPDATE: Boolean: lock the returned rows so that they can't be
         *     changed until the next COMMIT.
         *
         *   - DISTINCT: Boolean: return only unique result rows.
         *
         *   - GROUP BY: May be either an SQL fragment string naming a field or
         *     expression to group by, or an array of such SQL fragments.
         *
         *   - HAVING: May be either an string containing a HAVING clause or an array of
         *     conditions building the HAVING clause. If an array is given, the conditions
         *     constructed from each element are combined with AND.
         *
         *   - ORDER BY: May be either an SQL fragment giving a field name or
         *     expression to order by, or an array of such SQL fragments.
         *
         *   - USE INDEX: This may be either a string giving the index name to use
         *     for the query, or an array. If it is an associative array, each key
         *     gives the table name (or alias), each value gives the index name to
         *     use for that table. All strings are SQL fragments and so should be
         *     validated by the caller.
         *
         *   - EXPLAIN: In MySQL, this causes an EXPLAIN SELECT query to be run,
         *     instead of SELECT.
         *
         * And also the following boolean MySQL extensions, see the MySQL manual
         * for documentation:
         *
         *    - LOCK IN SHARE MODE
         *    - STRAIGHT_JOIN
         *    - HIGH_PRIORITY
         *    - SQL_BIG_RESULT
         *    - SQL_BUFFER_RESULT
         *    - SQL_SMALL_RESULT
         *    - SQL_CALC_FOUND_ROWS
         *    - SQL_CACHE
         *    - SQL_NO_CACHE
         *
         *
         * @param string|array $join_conds
         *
         * Optional associative array of table-specific join conditions. In the
         * most common case, this is unnecessary, since the join condition can be
         * in $conds. However, it is useful for doing a LEFT JOIN.
         *
         * The key of the array contains the table name or alias. The value is an
         * array with two elements, numbered 0 and 1. The first gives the type of
         * join, the second is the same as the $conds parameter. Thus it can be
         * an SQL fragment, or an array where the string keys are equality and the
         * numeric keys are SQL fragments all AND'd together. For example:
         *
         *    [ 'page' => [ 'LEFT JOIN', 'page_latest=rev_id' ] ]
         *
         * @return ResultWrapper|bool If the query returned no rows, a ResultWrapper
         *   with no rows in it will be returned. If there was a query error, a
         *   DBQueryError exception will be thrown, except if the "ignore errors"
         *   option was set, in which case false will be returned.
         */
        public function select(
                $table, $vars, $conds = '', $fname = __METHOD__,
                $options = [], $join_conds = []
        );

        /**
         * The equivalent of IDatabase::select() except that the constructed SQL
         * is returned, instead of being immediately executed. This can be useful for
         * doing UNION queries, where the SQL text of each query is needed. In general,
         * however, callers outside of Database classes should just use select().
         *
         * @param string|array $table Table name
         * @param string|array $vars Field names
         * @param string|array $conds Conditions
         * @param string $fname Caller function name
         * @param string|array $options Query options
         * @param string|array $join_conds Join conditions
         *
         * @return string SQL query string.
         * @see IDatabase::select()
         */
        public function selectSQLText(
                $table, $vars, $conds = '', $fname = __METHOD__,
                $options = [], $join_conds = []
        );

        /**
         * Single row SELECT wrapper. Equivalent to IDatabase::select(), except
         * that a single row object is returned. If the query returns no rows,
         * false is returned.
         *
         * @param string|array $table Table name
         * @param string|array $vars Field names
         * @param array $conds Conditions
         * @param string $fname Caller function name
         * @param string|array $options Query options
         * @param array|string $join_conds Join conditions
         *
         * @return stdClass|bool
         */
        public function selectRow( $table, $vars, $conds, $fname = __METHOD__,
                $options = [], $join_conds = []
        );

        /**
         * Estimate the number of rows in dataset
         *
         * MySQL allows you to estimate the number of rows that would be returned
         * by a SELECT query, using EXPLAIN SELECT. The estimate is provided using
         * index cardinality statistics, and is notoriously inaccurate, especially
         * when large numbers of rows have recently been added or deleted.
         *
         * For DBMSs that don't support fast result size estimation, this function
         * will actually perform the SELECT COUNT(*).
         *
         * Takes the same arguments as IDatabase::select().
         *
         * @param string $table Table name
         * @param string $vars Unused
         * @param array|string $conds Filters on the table
         * @param string $fname Function name for profiling
         * @param array $options Options for select
         * @return int Row count
         */
        public function estimateRowCount(
                $table, $vars = '*', $conds = '', $fname = __METHOD__, $options = []
        );

        /**
         * Get the number of rows in dataset
         *
         * This is useful when trying to do COUNT(*) but with a LIMIT for performance.
         *
         * Takes the same arguments as IDatabase::select().
         *
         * @since 1.27 Added $join_conds parameter
         *
         * @param array|string $tables Table names
         * @param string $vars Unused
         * @param array|string $conds Filters on the table
         * @param string $fname Function name for profiling
         * @param array $options Options for select
         * @param array $join_conds Join conditions (since 1.27)
         * @return int Row count
         */
        public function selectRowCount(
                $tables, $vars = '*', $conds = '', $fname = __METHOD__, $options = [], $join_conds = []
        );

        /**
         * Determines whether a field exists in a table
         *
         * @param string $table Table name
         * @param string $field Filed to check on that table
         * @param string $fname Calling function name (optional)
         * @return bool Whether $table has filed $field
         */
        public function fieldExists( $table, $field, $fname = __METHOD__ );

        /**
         * Determines whether an index exists
         * Usually throws a DBQueryError on failure
         * If errors are explicitly ignored, returns NULL on failure
         *
         * @param string $table
         * @param string $index
         * @param string $fname
         * @return bool|null
         */
        public function indexExists( $table, $index, $fname = __METHOD__ );

        /**
         * Query whether a given table exists
         *
         * @param string $table
         * @param string $fname
         * @return bool
         */
        public function tableExists( $table, $fname = __METHOD__ );

        /**
         * Determines if a given index is unique
         *
         * @param string $table
         * @param string $index
         *
         * @return bool
         */
        public function indexUnique( $table, $index );

        /**
         * INSERT wrapper, inserts an array into a table.
         *
         * $a may be either:
         *
         *   - A single associative array. The array keys are the field names, and
         *     the values are the values to insert. The values are treated as data
         *     and will be quoted appropriately. If NULL is inserted, this will be
         *     converted to a database NULL.
         *   - An array with numeric keys, holding a list of associative arrays.
         *     This causes a multi-row INSERT on DBMSs that support it. The keys in
         *     each subarray must be identical to each other, and in the same order.
         *
         * Usually throws a DBQueryError on failure. If errors are explicitly ignored,
         * returns success.
         *
         * $options is an array of options, with boolean options encoded as values
         * with numeric keys, in the same style as $options in
         * IDatabase::select(). Supported options are:
         *
         *   - IGNORE: Boolean: if present, duplicate key errors are ignored, and
         *     any rows which cause duplicate key errors are not inserted. It's
         *     possible to determine how many rows were successfully inserted using
         *     IDatabase::affectedRows().
         *
         * @param string $table Table name. This will be passed through
         *   DatabaseBase::tableName().
         * @param array $a Array of rows to insert
         * @param string $fname Calling function name (use __METHOD__) for logs/profiling
         * @param array $options Array of options
         *
         * @return bool
         */
        public function insert( $table, $a, $fname = __METHOD__, $options = [] );

        /**
         * UPDATE wrapper. Takes a condition array and a SET array.
         *
         * @param string $table Name of the table to UPDATE. This will be passed through
         *   DatabaseBase::tableName().
         * @param array $values An array of values to SET. For each array element,
         *   the key gives the field name, and the value gives the data to set
         *   that field to. The data will be quoted by IDatabase::addQuotes().
         * @param array $conds An array of conditions (WHERE). See
         *   IDatabase::select() for the details of the format of condition
         *   arrays. Use '*' to update all rows.
         * @param string $fname The function name of the caller (from __METHOD__),
         *   for logging and profiling.
         * @param array $options An array of UPDATE options, can be:
         *   - IGNORE: Ignore unique key conflicts
         *   - LOW_PRIORITY: MySQL-specific, see MySQL manual.
         * @return bool
         */
        public function update( $table, $values, $conds, $fname = __METHOD__, $options = [] );

        /**
         * Makes an encoded list of strings from an array
         *
         * @param array $a Containing the data
         * @param int $mode Constant
         *    - LIST_COMMA: Comma separated, no field names
         *    - LIST_AND:   ANDed WHERE clause (without the WHERE). See the
         *      documentation for $conds in IDatabase::select().
         *    - LIST_OR:    ORed WHERE clause (without the WHERE)
         *    - LIST_SET:   Comma separated with field names, like a SET clause
         *    - LIST_NAMES: Comma separated field names
         * @throws DBError
         * @return string
         */
        public function makeList( $a, $mode = LIST_COMMA );

        /**
         * Build a partial where clause from a 2-d array such as used for LinkBatch.
         * The keys on each level may be either integers or strings.
         *
         * @param array $data Organized as 2-d
         *    [ baseKeyVal => [ subKeyVal => [ignored], ... ], ... ]
         * @param string $baseKey Field name to match the base-level keys to (eg 'pl_namespace')
         * @param string $subKey Field name to match the sub-level keys to (eg 'pl_title')
         * @return string|bool SQL fragment, or false if no items in array
         */
        public function makeWhereFrom2d( $data, $baseKey, $subKey );

        /**
         * @param string $field
         * @return string
         */
        public function bitNot( $field );

        /**
         * @param string $fieldLeft
         * @param string $fieldRight
         * @return string
         */
        public function bitAnd( $fieldLeft, $fieldRight );

        /**
         * @param string $fieldLeft
         * @param string $fieldRight
         * @return string
         */
        public function bitOr( $fieldLeft, $fieldRight );

        /**
         * Build a concatenation list to feed into a SQL query
         * @param array $stringList List of raw SQL expressions; caller is
         *   responsible for any quoting
         * @return string
         */
        public function buildConcat( $stringList );

        /**
         * Build a GROUP_CONCAT or equivalent statement for a query.
         *
         * This is useful for combining a field for several rows into a single string.
         * NULL values will not appear in the output, duplicated values will appear,
         * and the resulting delimiter-separated values have no defined sort order.
         * Code using the results may need to use the PHP unique() or sort() methods.
         *
         * @param string $delim Glue to bind the results together
         * @param string|array $table Table name
         * @param string $field Field name
         * @param string|array $conds Conditions
         * @param string|array $join_conds Join conditions
         * @return string SQL text
         * @since 1.23
         */
        public function buildGroupConcatField(
                $delim, $table, $field, $conds = '', $join_conds = []
        );

        /**
         * Change the current database
         *
         * @param string $db
         * @return bool Success or failure
         */
        public function selectDB( $db );

        /**
         * Get the current DB name
         * @return string
         */
        public function getDBname();

        /**
         * Get the server hostname or IP address
         * @return string
         */
        public function getServer();

        /**
         * Adds quotes and backslashes.
         *
         * @param string|Blob $s
         * @return string
         */
        public function addQuotes( $s );

        /**
         * LIKE statement wrapper, receives a variable-length argument list with
         * parts of pattern to match containing either string literals that will be
         * escaped or tokens returned by anyChar() or anyString(). Alternatively,
         * the function could be provided with an array of aforementioned
         * parameters.
         *
         * Example: $dbr->buildLike( 'My_page_title/', $dbr->anyString() ) returns
         * a LIKE clause that searches for subpages of 'My page title'.
         * Alternatively:
         *   $pattern = [ 'My_page_title/', $dbr->anyString() ];
         *   $query .= $dbr->buildLike( $pattern );
         *
         * @since 1.16
         * @return string Fully built LIKE statement
         */
        public function buildLike();

        /**
         * Returns a token for buildLike() that denotes a '_' to be used in a LIKE query
         *
         * @return LikeMatch
         */
        public function anyChar();

        /**
         * Returns a token for buildLike() that denotes a '%' to be used in a LIKE query
         *
         * @return LikeMatch
         */
        public function anyString();

        /**
         * Returns an appropriately quoted sequence value for inserting a new row.
         * MySQL has autoincrement fields, so this is just NULL. But the PostgreSQL
         * subclass will return an integer, and save the value for insertId()
         *
         * Any implementation of this function should *not* involve reusing
         * sequence numbers created for rolled-back transactions.
         * See http://bugs.mysql.com/bug.php?id=30767 for details.
         * @param string $seqName
         * @return null|int
         */
        public function nextSequenceValue( $seqName );

        /**
         * REPLACE query wrapper.
         *
         * REPLACE is a very handy MySQL extension, which functions like an INSERT
         * except that when there is a duplicate key error, the old row is deleted
         * and the new row is inserted in its place.
         *
         * We simulate this with standard SQL with a DELETE followed by INSERT. To
         * perform the delete, we need to know what the unique indexes are so that
         * we know how to find the conflicting rows.
         *
         * It may be more efficient to leave off unique indexes which are unlikely
         * to collide. However if you do this, you run the risk of encountering
         * errors which wouldn't have occurred in MySQL.
         *
         * @param string $table The table to replace the row(s) in.
         * @param array $uniqueIndexes Is an array of indexes. Each element may be either
         *    a field name or an array of field names
         * @param array $rows Can be either a single row to insert, or multiple rows,
         *    in the same format as for IDatabase::insert()
         * @param string $fname Calling function name (use __METHOD__) for logs/profiling
         */
        public function replace( $table, $uniqueIndexes, $rows, $fname = __METHOD__ );

        /**
         * INSERT ON DUPLICATE KEY UPDATE wrapper, upserts an array into a table.
         *
         * This updates any conflicting rows (according to the unique indexes) using
         * the provided SET clause and inserts any remaining (non-conflicted) rows.
         *
         * $rows may be either:
         *   - A single associative array. The array keys are the field names, and
         *     the values are the values to insert. The values are treated as data
         *     and will be quoted appropriately. If NULL is inserted, this will be
         *     converted to a database NULL.
         *   - An array with numeric keys, holding a list of associative arrays.
         *     This causes a multi-row INSERT on DBMSs that support it. The keys in
         *     each subarray must be identical to each other, and in the same order.
         *
         * It may be more efficient to leave off unique indexes which are unlikely
         * to collide. However if you do this, you run the risk of encountering
         * errors which wouldn't have occurred in MySQL.
         *
         * Usually throws a DBQueryError on failure. If errors are explicitly ignored,
         * returns success.
         *
         * @since 1.22
         *
         * @param string $table Table name. This will be passed through DatabaseBase::tableName().
         * @param array $rows A single row or list of rows to insert
         * @param array $uniqueIndexes List of single field names or field name tuples
         * @param array $set An array of values to SET. For each array element, the
         *   key gives the field name, and the value gives the data to set that
         *   field to. The data will be quoted by IDatabase::addQuotes().
         * @param string $fname Calling function name (use __METHOD__) for logs/profiling
         * @throws Exception
         * @return bool
         */
        public function upsert(
                $table, array $rows, array $uniqueIndexes, array $set, $fname = __METHOD__
        );

        /**
         * DELETE where the condition is a join.
         *
         * MySQL overrides this to use a multi-table DELETE syntax, in other databases
         * we use sub-selects
         *
         * For safety, an empty $conds will not delete everything. If you want to
         * delete all rows where the join condition matches, set $conds='*'.
         *
         * DO NOT put the join condition in $conds.
         *
         * @param string $delTable The table to delete from.
         * @param string $joinTable The other table.
         * @param string $delVar The variable to join on, in the first table.
         * @param string $joinVar The variable to join on, in the second table.
         * @param array $conds Condition array of field names mapped to variables,
         *   ANDed together in the WHERE clause
         * @param string $fname Calling function name (use __METHOD__) for logs/profiling
         * @throws DBUnexpectedError
         */
        public function deleteJoin( $delTable, $joinTable, $delVar, $joinVar, $conds,
                $fname = __METHOD__
        );

        /**
         * DELETE query wrapper.
         *
         * @param array $table Table name
         * @param string|array $conds Array of conditions. See $conds in IDatabase::select()
         *   for the format. Use $conds == "*" to delete all rows
         * @param string $fname Name of the calling function
         * @throws DBUnexpectedError
         * @return bool|ResultWrapper
         */
        public function delete( $table, $conds, $fname = __METHOD__ );

        /**
         * INSERT SELECT wrapper. Takes data from a SELECT query and inserts it
         * into another table.
         *
         * @param string $destTable The table name to insert into
         * @param string|array $srcTable May be either a table name, or an array of table names
         *    to include in a join.
         *
         * @param array $varMap Must be an associative array of the form
         *    [ 'dest1' => 'source1', ... ]. Source items may be literals
         *    rather than field names, but strings should be quoted with
         *    IDatabase::addQuotes()
         *
         * @param array $conds Condition array. See $conds in IDatabase::select() for
         *    the details of the format of condition arrays. May be "*" to copy the
         *    whole table.
         *
         * @param string $fname The function name of the caller, from __METHOD__
         *
         * @param array $insertOptions Options for the INSERT part of the query, see
         *    IDatabase::insert() for details.
         * @param array $selectOptions Options for the SELECT part of the query, see
         *    IDatabase::select() for details.
         *
         * @return ResultWrapper
         */
        public function insertSelect( $destTable, $srcTable, $varMap, $conds,
                $fname = __METHOD__,
                $insertOptions = [], $selectOptions = []
        );

        /**
         * Returns true if current database backend supports ORDER BY or LIMIT for separate subqueries
         * within the UNION construct.
         * @return bool
         */
        public function unionSupportsOrderAndLimit();

        /**
         * Construct a UNION query
         * This is used for providing overload point for other DB abstractions
         * not compatible with the MySQL syntax.
         * @param array $sqls SQL statements to combine
         * @param bool $all Use UNION ALL
         * @return string SQL fragment
         */
        public function unionQueries( $sqls, $all );

        /**
         * Returns an SQL expression for a simple conditional. This doesn't need
         * to be overridden unless CASE isn't supported in your DBMS.
         *
         * @param string|array $cond SQL expression which will result in a boolean value
         * @param string $trueVal SQL expression to return if true
         * @param string $falseVal SQL expression to return if false
         * @return string SQL fragment
         */
        public function conditional( $cond, $trueVal, $falseVal );

        /**
         * Returns a comand for str_replace function in SQL query.
         * Uses REPLACE() in MySQL
         *
         * @param string $orig Column to modify
         * @param string $old Column to seek
         * @param string $new Column to replace with
         *
         * @return string
         */
        public function strreplace( $orig, $old, $new );

        /**
         * Determines how long the server has been up
         *
         * @return int
         */
        public function getServerUptime();

        /**
         * Determines if the last failure was due to a deadlock
         *
         * @return bool
         */
        public function wasDeadlock();

        /**
         * Determines if the last failure was due to a lock timeout
         *
         * @return bool
         */
        public function wasLockTimeout();

        /**
         * Determines if the last query error was due to a dropped connection and should
         * be dealt with by pinging the connection and reissuing the query.
         *
         * @return bool
         */
        public function wasErrorReissuable();

        /**
         * Determines if the last failure was due to the database being read-only.
         *
         * @return bool
         */
        public function wasReadOnlyError();

        /**
         * Wait for the replica DB to catch up to a given master position
         *
         * @param DBMasterPos $pos
         * @param int $timeout The maximum number of seconds to wait for synchronisation
         * @return int|null Zero if the replica DB was past that position already,
         *   greater than zero if we waited for some period of time, less than
         *   zero if it timed out, and null on error
         */
        public function masterPosWait( DBMasterPos $pos, $timeout );

        /**
         * Get the replication position of this replica DB
         *
         * @return DBMasterPos|bool False if this is not a replica DB.
         */
        public function getSlavePos();

        /**
         * Get the position of this master
         *
         * @return DBMasterPos|bool False if this is not a master
         */
        public function getMasterPos();

        /**
         * @return bool Whether the DB is marked as read-only server-side
         * @since 1.28
         */
        public function serverIsReadOnly();

        /**
         * Run a callback as soon as the current transaction commits or rolls back.
         * An error is thrown if no transaction is pending. Queries in the function will run in
         * AUTO-COMMIT mode unless there are begin() calls. Callbacks must commit any transactions
         * that they begin.
         *
         * This is useful for combining cooperative locks and DB transactions.
         *
         * The callback takes one argument:
         *   - How the transaction ended (IDatabase::TRIGGER_COMMIT or IDatabase::TRIGGER_ROLLBACK)
         *
         * @param callable $callback
         * @param string $fname Caller name
         * @return mixed
         * @since 1.28
         */
        public function onTransactionResolution( callable $callback, $fname = __METHOD__ );

        /**
         * Run a callback as soon as there is no transaction pending.
         * If there is a transaction and it is rolled back, then the callback is cancelled.
         * Queries in the function will run in AUTO-COMMIT mode unless there are begin() calls.
         * Callbacks must commit any transactions that they begin.
         *
         * This is useful for updates to different systems or when separate transactions are needed.
         * For example, one might want to enqueue jobs into a system outside the database, but only
         * after the database is updated so that the jobs will see the data when they actually run.
         * It can also be used for updates that easily cause deadlocks if locks are held too long.
         *
         * Updates will execute in the order they were enqueued.
         *
         * The callback takes one argument:
         *   - How the transaction ended (IDatabase::TRIGGER_COMMIT or IDatabase::TRIGGER_IDLE)
         *
         * @param callable $callback
         * @param string $fname Caller name
         * @since 1.20
         */
        public function onTransactionIdle( callable $callback, $fname = __METHOD__ );

        /**
         * Run a callback before the current transaction commits or now if there is none.
         * If there is a transaction and it is rolled back, then the callback is cancelled.
         * Callbacks must not start nor commit any transactions. If no transaction is active,
         * then a transaction will wrap the callback.
         *
         * This is useful for updates that easily cause deadlocks if locks are held too long
         * but where atomicity is strongly desired for these updates and some related updates.
         *
         * Updates will execute in the order they were enqueued.
         *
         * @param callable $callback
         * @param string $fname Caller name
         * @since 1.22
         */
        public function onTransactionPreCommitOrIdle( callable $callback, $fname = __METHOD__ );

        /**
         * Run a callback each time any transaction commits or rolls back
         *
         * The callback takes two arguments:
         *   - IDatabase::TRIGGER_COMMIT or IDatabase::TRIGGER_ROLLBACK
         *   - This IDatabase object
         * Callbacks must commit any transactions that they begin.
         *
         * Registering a callback here will not affect writesOrCallbacks() pending
         *
         * @param string $name Callback name
         * @param callable|null $callback Use null to unset a listener
         * @return mixed
         * @since 1.28
         */
        public function setTransactionListener( $name, callable $callback = null );

        /**
         * Begin an atomic section of statements
         *
         * If a transaction has been started already, just keep track of the given
         * section name to make sure the transaction is not committed pre-maturely.
         * This function can be used in layers (with sub-sections), so use a stack
         * to keep track of the different atomic sections. If there is no transaction,
         * start one implicitly.
         *
         * The goal of this function is to create an atomic section of SQL queries
         * without having to start a new transaction if it already exists.
         *
         * Atomic sections are more strict than transactions. With transactions,
         * attempting to begin a new transaction when one is already running results
         * in MediaWiki issuing a brief warning and doing an implicit commit. All
         * atomic levels *must* be explicitly closed using IDatabase::endAtomic(),
         * and any database transactions cannot be began or committed until all atomic
         * levels are closed. There is no such thing as implicitly opening or closing
         * an atomic section.
         *
         * @since 1.23
         * @param string $fname
         * @throws DBError
         */
        public function startAtomic( $fname = __METHOD__ );

        /**
         * Ends an atomic section of SQL statements
         *
         * Ends the next section of atomic SQL statements and commits the transaction
         * if necessary.
         *
         * @since 1.23
         * @see IDatabase::startAtomic
         * @param string $fname
         * @throws DBError
         */
        public function endAtomic( $fname = __METHOD__ );

        /**
         * Run a callback to do an atomic set of updates for this database
         *
         * The $callback takes the following arguments:
         *   - This database object
         *   - The value of $fname
         *
         * If any exception occurs in the callback, then rollback() will be called and the error will
         * be re-thrown. It may also be that the rollback itself fails with an exception before then.
         * In any case, such errors are expected to terminate the request, without any outside caller
         * attempting to catch errors and commit anyway. Note that any rollback undoes all prior
         * atomic section and uncommitted updates, which trashes the current request, requiring an
         * error to be displayed.
         *
         * This can be an alternative to explicit startAtomic()/endAtomic() calls.
         *
         * @see DatabaseBase::startAtomic
         * @see DatabaseBase::endAtomic
         *
         * @param string $fname Caller name (usually __METHOD__)
         * @param callable $callback Callback that issues DB updates
         * @return mixed $res Result of the callback (since 1.28)
         * @throws DBError
         * @throws RuntimeException
         * @throws UnexpectedValueException
         * @since 1.27
         */
        public function doAtomicSection( $fname, callable $callback );

        /**
         * Begin a transaction. If a transaction is already in progress,
         * that transaction will be committed before the new transaction is started.
         *
         * Only call this from code with outer transcation scope.
         * See https://www.mediawiki.org/wiki/Database_transactions for details.
         * Nesting of transactions is not supported.
         *
         * Note that when the DBO_TRX flag is set (which is usually the case for web
         * requests, but not for maintenance scripts), any previous database query
         * will have started a transaction automatically.
         *
         * Nesting of transactions is not supported. Attempts to nest transactions
         * will cause a warning, unless the current transaction was started
         * automatically because of the DBO_TRX flag.
         *
         * @param string $fname Calling function name
         * @param string $mode A situationally valid IDatabase::TRANSACTION_* constant [optional]
         * @throws DBError
         */
        public function begin( $fname = __METHOD__, $mode = self::TRANSACTION_EXPLICIT );

        /**
         * Commits a transaction previously started using begin().
         * If no transaction is in progress, a warning is issued.
         *
         * Only call this from code with outer transcation scope.
         * See https://www.mediawiki.org/wiki/Database_transactions for details.
         * Nesting of transactions is not supported.
         *
         * @param string $fname
         * @param string $flush Flush flag, set to situationally valid IDatabase::FLUSHING_*
         *   constant to disable warnings about explicitly committing implicit transactions,
         *   or calling commit when no transaction is in progress.
         *
         *   This will trigger an exception if there is an ongoing explicit transaction.
         *
         *   Only set the flush flag if you are sure that these warnings are not applicable,
         *   and no explicit transactions are open.
         *
         * @throws DBUnexpectedError
         */
        public function commit( $fname = __METHOD__, $flush = '' );

        /**
         * Rollback a transaction previously started using begin().
         * If no transaction is in progress, a warning is issued.
         *
         * Only call this from code with outer transcation scope.
         * See https://www.mediawiki.org/wiki/Database_transactions for details.
         * Nesting of transactions is not supported. If a serious unexpected error occurs,
         * throwing an Exception is preferrable, using a pre-installed error handler to trigger
         * rollback (in any case, failure to issue COMMIT will cause rollback server-side).
         *
         * @param string $fname Calling function name
         * @param string $flush Flush flag, set to a situationally valid IDatabase::FLUSHING_*
         *   constant to disable warnings about calling rollback when no transaction is in
         *   progress. This will silently break any ongoing explicit transaction. Only set the
         *   flush flag if you are sure that it is safe to ignore these warnings in your context.
         * @throws DBUnexpectedError
         * @since 1.23 Added $flush parameter
         */
        public function rollback( $fname = __METHOD__, $flush = '' );

        /**
         * Commit any transaction but error out if writes or callbacks are pending
         *
         * This is intended for clearing out REPEATABLE-READ snapshots so that callers can
         * see a new point-in-time of the database. This is useful when one of many transaction
         * rounds finished and significant time will pass in the script's lifetime. It is also
         * useful to call on a replica DB after waiting on replication to catch up to the master.
         *
         * @param string $fname Calling function name
         * @throws DBUnexpectedError
         * @since 1.28
         */
        public function flushSnapshot( $fname = __METHOD__ );

        /**
         * List all tables on the database
         *
         * @param string $prefix Only show tables with this prefix, e.g. mw_
         * @param string $fname Calling function name
         * @throws DBError
         * @return array
         */
        public function listTables( $prefix = null, $fname = __METHOD__ );

        /**
         * Convert a timestamp in one of the formats accepted by wfTimestamp()
         * to the format used for inserting into timestamp fields in this DBMS.
         *
         * The result is unquoted, and needs to be passed through addQuotes()
         * before it can be included in raw SQL.
         *
         * @param string|int $ts
         *
         * @return string
         */
        public function timestamp( $ts = 0 );

        /**
         * Convert a timestamp in one of the formats accepted by wfTimestamp()
         * to the format used for inserting into timestamp fields in this DBMS. If
         * NULL is input, it is passed through, allowing NULL values to be inserted
         * into timestamp fields.
         *
         * The result is unquoted, and needs to be passed through addQuotes()
         * before it can be included in raw SQL.
         *
         * @param string|int $ts
         *
         * @return string
         */
        public function timestampOrNull( $ts = null );

        /**
         * Ping the server and try to reconnect if it there is no connection
         *
         * @param float|null &$rtt Value to store the estimated RTT [optional]
         * @return bool Success or failure
         */
        public function ping( &$rtt = null );

        /**
         * Get replica DB lag. Currently supported only by MySQL.
         *
         * Note that this function will generate a fatal error on many
         * installations. Most callers should use LoadBalancer::safeGetLag()
         * instead.
         *
         * @return int|bool Database replication lag in seconds or false on error
         */
        public function getLag();

        /**
         * Get the replica DB lag when the current transaction started
         * or a general lag estimate if not transaction is active
         *
         * This is useful when transactions might use snapshot isolation
         * (e.g. REPEATABLE-READ in innodb), so the "real" lag of that data
         * is this lag plus transaction duration. If they don't, it is still
         * safe to be pessimistic. In AUTO-COMMIT mode, this still gives an
         * indication of the staleness of subsequent reads.
         *
         * @return array ('lag': seconds or false on error, 'since': UNIX timestamp of BEGIN)
         * @since 1.27
         */
        public function getSessionLagStatus();

        /**
         * Return the maximum number of items allowed in a list, or 0 for unlimited.
         *
         * @return int
         */
        public function maxListLen();

        /**
         * Some DBMSs have a special format for inserting into blob fields, they
         * don't allow simple quoted strings to be inserted. To insert into such
         * a field, pass the data through this function before passing it to
         * IDatabase::insert().
         *
         * @param string $b
         * @return string
         */
        public function encodeBlob( $b );

        /**
         * Some DBMSs return a special placeholder object representing blob fields
         * in result objects. Pass the object through this function to return the
         * original string.
         *
         * @param string|Blob $b
         * @return string
         */
        public function decodeBlob( $b );

        /**
         * Override database's default behavior. $options include:
         *     'connTimeout' : Set the connection timeout value in seconds.
         *                     May be useful for very long batch queries such as
         *                     full-wiki dumps, where a single query reads out over
         *                     hours or days.
         *
         * @param array $options
         * @return void
         */
        public function setSessionOptions( array $options );

        /**
         * Set variables to be used in sourceFile/sourceStream, in preference to the
         * ones in $GLOBALS. If an array is set here, $GLOBALS will not be used at
         * all. If it's set to false, $GLOBALS will be used.
         *
         * @param bool|array $vars Mapping variable name to value.
         */
        public function setSchemaVars( $vars );

        /**
         * Check to see if a named lock is available (non-blocking)
         *
         * @param string $lockName Name of lock to poll
         * @param string $method Name of method calling us
         * @return bool
         * @since 1.20
         */
        public function lockIsFree( $lockName, $method );

        /**
         * Acquire a named lock
         *
         * Named locks are not related to transactions
         *
         * @param string $lockName Name of lock to aquire
         * @param string $method Name of the calling method
         * @param int $timeout Acquisition timeout in seconds
         * @return bool
         */
        public function lock( $lockName, $method, $timeout = 5 );

        /**
         * Release a lock
         *
         * Named locks are not related to transactions
         *
         * @param string $lockName Name of lock to release
         * @param string $method Name of the calling method
         *
         * @return int Returns 1 if the lock was released, 0 if the lock was not established
         * by this thread (in which case the lock is not released), and NULL if the named
         * lock did not exist
         */
        public function unlock( $lockName, $method );

        /**
         * Acquire a named lock, flush any transaction, and return an RAII style unlocker object
         *
         * Only call this from outer transcation scope and when only one DB will be affected.
         * See https://www.mediawiki.org/wiki/Database_transactions for details.
         *
         * This is suitiable for transactions that need to be serialized using cooperative locks,
         * where each transaction can see each others' changes. Any transaction is flushed to clear
         * out stale REPEATABLE-READ snapshot data. Once the returned object falls out of PHP scope,
         * the lock will be released unless a transaction is active. If one is active, then the lock
         * will be released when it either commits or rolls back.
         *
         * If the lock acquisition failed, then no transaction flush happens, and null is returned.
         *
         * @param string $lockKey Name of lock to release
         * @param string $fname Name of the calling method
         * @param int $timeout Acquisition timeout in seconds
         * @return ScopedCallback|null
         * @throws DBUnexpectedError
         * @since 1.27
         */
        public function getScopedLockAndFlush( $lockKey, $fname, $timeout );

        /**
         * Check to see if a named lock used by lock() use blocking queues
         *
         * @return bool
         * @since 1.26
         */
        public function namedLocksEnqueue();

        /**
         * Find out when 'infinity' is. Most DBMSes support this. This is a special
         * keyword for timestamps in PostgreSQL, and works with CHAR(14) as well
         * because "i" sorts after all numbers.
         *
         * @return string
         */
        public function getInfinity();

        /**
         * Encode an expiry time into the DBMS dependent format
         *
         * @param string $expiry Timestamp for expiry, or the 'infinity' string
         * @return string
         */
        public function encodeExpiry( $expiry );

        /**
         * Decode an expiry time into a DBMS independent format
         *
         * @param string $expiry DB timestamp field value for expiry
         * @param int $format TS_* constant, defaults to TS_MW
         * @return string
         */
        public function decodeExpiry( $expiry, $format = TS_MW );

        /**
         * Allow or deny "big selects" for this session only. This is done by setting
         * the sql_big_selects session variable.
         *
         * This is a MySQL-specific feature.
         *
         * @param bool|string $value True for allow, false for deny, or "default" to
         *   restore the initial value
         */
        public function setBigSelects( $value = true );

        /**
         * @return bool Whether this DB is read-only
         * @since 1.27
         */
        public function isReadOnly();

        /**
         * Make certain table names use their own database, schema, and table prefix
         * when passed into SQL queries pre-escaped and without a qualified database name
         *
         * For example, "user" can be converted to "myschema.mydbname.user" for convenience.
         * Appearances like `user`, somedb.user, somedb.someschema.user will used literally.
         *
         * Calling this twice will completely clear any old table aliases. Also, note that
         * callers are responsible for making sure the schemas and databases actually exist.
         *
         * @param array[] $aliases Map of (table => (dbname, schema, prefix) map)
         * @since 1.28
         */
        public function setTableAliases( array $aliases );
}