Follow-up 36f4daf32c: allow no-write database connections to use transactions

After 36f4daf32c was merged, Aaron pointed out on Gerrit that:

    Transaction can be used on replicas for REPEATABLE-READ mode, so
    queries in that transaction see the same version of the DB. Those
    do not involve writes and things would probably break sometimes
    without it (like reads following foreign keys and reference in
    separate queries).

So allow no-write connections to call begin() and commit(), and only
throw an exception when a write query is attempted.

Bug: T183265
Change-Id: I138677a714df13ead08061c3e9ef794c3befbe9d

diff --git a/includes/libs/rdbms/database/Database.php b/includes/libs/rdbms/database/Database.php
index 1c9cad5..3d40417 100644 (file)
--- a/includes/libs/rdbms/database/Database.php
+++ b/includes/libs/rdbms/database/Database.php
@@ -2965,13 +2965,6 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
        }
 
        final public function begin( $fname = __METHOD__, $mode = self::TRANSACTION_EXPLICIT ) {
        }
 
        final public function begin( $fname = __METHOD__, $mode = self::TRANSACTION_EXPLICIT ) {

-               if ( !$this->allowWrite ) {
-                       throw new DBError(
-                               $this,
-                               'Write operations are not allowed on this database connection!'
-                       );
-               }
-

                // Protect against mismatched atomic section, transaction nesting, and snapshot loss
                if ( $this->mTrxLevel ) {
                        if ( $this->mTrxAtomicLevels ) {
                // Protect against mismatched atomic section, transaction nesting, and snapshot loss
                if ( $this->mTrxLevel ) {
                        if ( $this->mTrxAtomicLevels ) {


@@ -3033,14 +3026,6 @@ abstract class Database implements IDatabase, IMaintainableDatabase, LoggerAware
        }
 
        final public function commit( $fname = __METHOD__, $flush = '' ) {
        }
 
        final public function commit( $fname = __METHOD__, $flush = '' ) {

-               if ( !$this->allowWrite ) {
-                       // we should never get here, since begin() would already throw
-                       throw new DBError(
-                               $this,
-                               'Write operations are not allowed on this database connection!'
-                       );
-               }
-

                if ( $this->mTrxLevel && $this->mTrxAtomicLevels ) {
                        // There are still atomic sections open. This cannot be ignored
                        $levels = implode( ', ', $this->mTrxAtomicLevels );
                if ( $this->mTrxLevel && $this->mTrxAtomicLevels ) {
                        // There are still atomic sections open. This cannot be ignored
                        $levels = implode( ', ', $this->mTrxAtomicLevels );