$row = null;
}
+ // Callers doing updates will pass in READ_LATEST as usual. Since the text/blob tables
+ // do not normally get rows changed around, set READ_LATEST_IMMUTABLE in those cases.
+ $flags = $this->mQueryFlags;
+ $flags |= DBAccessObjectUtils::hasFlags( $flags, self::READ_LATEST )
+ ? self::READ_LATEST_IMMUTABLE
+ : 0;
+
+ list( $index, $options, $fallbackIndex, $fallbackOptions ) =
+ DBAccessObjectUtils::getDBOptions( $flags );
+
if ( !$row ) {
// Text data is immutable; check replica DBs first.
- $dbr = wfGetDB( DB_REPLICA );
- $row = $dbr->selectRow( 'text',
+ $row = wfGetDB( $index )->selectRow(
+ 'text',
[ 'old_text', 'old_flags' ],
[ 'old_id' => $textId ],
- __METHOD__ );
+ __METHOD__,
+ $options
+ );
}
- // Fallback to the master in case of replica DB lag. Also use FOR UPDATE if it was
- // used to fetch this revision to avoid missing the row due to REPEATABLE-READ.
- $forUpdate = ( $this->mQueryFlags & self::READ_LOCKING == self::READ_LOCKING );
- if ( !$row && ( $forUpdate || wfGetLB()->getServerCount() > 1 ) ) {
- $dbw = wfGetDB( DB_MASTER );
- $row = $dbw->selectRow( 'text',
+ // Fallback to DB_MASTER in some cases if the row was not found
+ if ( !$row && $fallbackIndex !== null ) {
+ // Use FOR UPDATE if it was used to fetch this revision. This avoids missing the row
+ // due to REPEATABLE-READ. Also fallback to the master if READ_LATEST is provided.
+ $row = wfGetDB( $fallbackIndex )->selectRow(
+ 'text',
[ 'old_text', 'old_flags' ],
[ 'old_id' => $textId ],
__METHOD__,
- $forUpdate ? [ 'FOR UPDATE' ] : [] );
+ $fallbackOptions
+ );
}
if ( !$row ) {
*
* @since 1.26
*/
-class DBAccessObjectUtils {
+class DBAccessObjectUtils implements IDBAccessObject {
/**
* @param integer $bitfield
* @param integer $flags IDBAccessObject::READ_* constant
}
/**
- * Get an appropriate DB index and options for a query
+ * Get an appropriate DB index, options, and fallback DB index for a query
*
- * @param integer $bitfield
- * @return array (DB_MASTER/DB_REPLICA, SELECT options array)
+ * The fallback DB index and options are to be used if the entity is not found
+ * with the initial DB index, typically querying the master DB to avoid lag
+ *
+ * @param integer $bitfield Bitfield of IDBAccessObject::READ_* constants
+ * @return array List of DB indexes and options in this order:
+ * - DB_MASTER or DB_REPLICA constant for the initial query
+ * - SELECT options array for the initial query
+ * - DB_MASTER constant for the fallback query; null if no fallback should happen
+ * - SELECT options array for the fallback query; empty if no fallback should happen
*/
public static function getDBOptions( $bitfield ) {
- $index = self::hasFlags( $bitfield, IDBAccessObject::READ_LATEST )
- ? DB_MASTER
- : DB_REPLICA;
+ if ( self::hasFlags( $bitfield, self::READ_LATEST_IMMUTABLE ) ) {
+ $index = DB_REPLICA; // override READ_LATEST if set
+ $fallbackIndex = DB_MASTER;
+ } elseif ( self::hasFlags( $bitfield, self::READ_LATEST ) ) {
+ $index = DB_MASTER;
+ $fallbackIndex = null;
+ } else {
+ $index = DB_REPLICA;
+ $fallbackIndex = null;
+ }
+
+ $lockingOptions = [];
+ if ( self::hasFlags( $bitfield, self::READ_EXCLUSIVE ) ) {
+ $lockingOptions[] = 'FOR UPDATE';
+ } elseif ( self::hasFlags( $bitfield, self::READ_LOCKING ) ) {
+ $lockingOptions[] = 'LOCK IN SHARE MODE';
+ }
- $options = [];
- if ( self::hasFlags( $bitfield, IDBAccessObject::READ_EXCLUSIVE ) ) {
- $options[] = 'FOR UPDATE';
- } elseif ( self::hasFlags( $bitfield, IDBAccessObject::READ_LOCKING ) ) {
- $options[] = 'LOCK IN SHARE MODE';
+ if ( $fallbackIndex !== null ) {
+ $options = []; // locks on DB_REPLICA make no sense
+ $fallbackOptions = $lockingOptions;
+ } else {
+ $options = $lockingOptions;
+ $fallbackOptions = []; // no fallback
}
- return [ $index, $options ];
+ return [ $index, $options, $fallbackIndex, $fallbackOptions ];
}
}