DatabasePostgres.php

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<?php
use Wikimedia\WaitConditionLoop;

class DatabasePostgres extends Database {
    protected $port;

    protected $mLastResult = null;
    protected $mAffectedRows = null;

    private $mInsertId = null;
    private $numericVersion = null;
    private $connectString;
    private $mCoreSchema;

    public function __construct( array $params ) {
        $this->port = isset( $params['port'] ) ? $params['port'] : false;
        parent::__construct( $params );
    }

    function getType() {
        return 'postgres';
    }

    function implicitGroupby() {
        return false;
    }

    function implicitOrderby() {
        return false;
    }

    function hasConstraint( $name ) {
        $conn = $this->getBindingHandle();

        $sql = "SELECT 1 FROM pg_catalog.pg_constraint c, pg_catalog.pg_namespace n " .
            "WHERE c.connamespace = n.oid AND conname = '" .
            pg_escape_string( $conn, $name ) . "' AND n.nspname = '" .
            pg_escape_string( $conn, $this->getCoreSchema() ) . "'";
        $res = $this->doQuery( $sql );

        return $this->numRows( $res );
    }

    function open( $server, $user, $password, $dbName ) {
        # Test for Postgres support, to avoid suppressed fatal error
        if ( !function_exists( 'pg_connect' ) ) {
            throw new DBConnectionError(
                $this,
                "Postgres functions missing, have you compiled PHP with the --with-pgsql\n" .
                "option? (Note: if you recently installed PHP, you may need to restart your\n" .
                "webserver and database)\n"
            );
        }

        $this->mServer = $server;
        $this->mUser = $user;
        $this->mPassword = $password;
        $this->mDBname = $dbName;

        $connectVars = [
            'dbname' => $dbName,
            'user' => $user,
            'password' => $password
        ];
        if ( $server != false && $server != '' ) {
            $connectVars['host'] = $server;
        }
        if ( (int)$this->port > 0 ) {
            $connectVars['port'] = (int)$this->port;
        }
        if ( $this->mFlags & self::DBO_SSL ) {
            $connectVars['sslmode'] = 1;
        }

        $this->connectString = $this->makeConnectionString( $connectVars );
        $this->close();
        $this->installErrorHandler();

        try {
            // Use new connections to let LoadBalancer/LBFactory handle reuse
            $this->mConn = pg_connect( $this->connectString, PGSQL_CONNECT_FORCE_NEW );
        } catch ( Exception $ex ) {
            $this->restoreErrorHandler();
            throw $ex;
        }

        $phpError = $this->restoreErrorHandler();

        if ( !$this->mConn ) {
            $this->queryLogger->debug(
                "DB connection error\n" .
                "Server: $server, Database: $dbName, User: $user, Password: " .
                substr( $password, 0, 3 ) . "...\n"
            );
            $this->queryLogger->debug( $this->lastError() . "\n" );
            throw new DBConnectionError( $this, str_replace( "\n", ' ', $phpError ) );
        }

        $this->mOpened = true;

        # If called from the command-line (e.g. importDump), only show errors
        if ( $this->cliMode ) {
            $this->doQuery( "SET client_min_messages = 'ERROR'" );
        }

        $this->query( "SET client_encoding='UTF8'", __METHOD__ );
        $this->query( "SET datestyle = 'ISO, YMD'", __METHOD__ );
        $this->query( "SET timezone = 'GMT'", __METHOD__ );
        $this->query( "SET standard_conforming_strings = on", __METHOD__ );
        if ( $this->getServerVersion() >= 9.0 ) {
            $this->query( "SET bytea_output = 'escape'", __METHOD__ ); // PHP bug 53127
        }

        $this->determineCoreSchema( $this->mSchema );
        // The schema to be used is now in the search path; no need for explicit qualification
        $this->mSchema = null;

        return $this->mConn;
    }

    function selectDB( $db ) {
        if ( $this->mDBname !== $db ) {
            return (bool)$this->open( $this->mServer, $this->mUser, $this->mPassword, $db );
        } else {
            return true;
        }
    }

    function makeConnectionString( $vars ) {
        $s = '';
        foreach ( $vars as $name => $value ) {
            $s .= "$name='" . str_replace( "'", "\\'", $value ) . "' ";
        }

        return $s;
    }

    protected function closeConnection() {
        return $this->mConn ? pg_close( $this->mConn ) : true;
    }

    public function doQuery( $sql ) {
        $conn = $this->getBindingHandle();

        $sql = mb_convert_encoding( $sql, 'UTF-8' );
        // Clear previously left over PQresult
        while ( $res = pg_get_result( $conn ) ) {
            pg_free_result( $res );
        }
        if ( pg_send_query( $conn, $sql ) === false ) {
            throw new DBUnexpectedError( $this, "Unable to post new query to PostgreSQL\n" );
        }
        $this->mLastResult = pg_get_result( $conn );
        $this->mAffectedRows = null;
        if ( pg_result_error( $this->mLastResult ) ) {
            return false;
        }

        return $this->mLastResult;
    }

    protected function dumpError() {
        $diags = [
            PGSQL_DIAG_SEVERITY,
            PGSQL_DIAG_SQLSTATE,
            PGSQL_DIAG_MESSAGE_PRIMARY,
            PGSQL_DIAG_MESSAGE_DETAIL,
            PGSQL_DIAG_MESSAGE_HINT,
            PGSQL_DIAG_STATEMENT_POSITION,
            PGSQL_DIAG_INTERNAL_POSITION,
            PGSQL_DIAG_INTERNAL_QUERY,
            PGSQL_DIAG_CONTEXT,
            PGSQL_DIAG_SOURCE_FILE,
            PGSQL_DIAG_SOURCE_LINE,
            PGSQL_DIAG_SOURCE_FUNCTION
        ];
        foreach ( $diags as $d ) {
            $this->queryLogger->debug( sprintf( "PgSQL ERROR(%d): %s\n",
                $d, pg_result_error_field( $this->mLastResult, $d ) ) );
        }
    }

    function reportQueryError( $error, $errno, $sql, $fname, $tempIgnore = false ) {
        if ( $tempIgnore ) {
            /* Check for constraint violation */
            if ( $errno === '23505' ) {
                parent::reportQueryError( $error, $errno, $sql, $fname, $tempIgnore );

                return;
            }
        }
        /* Transaction stays in the ERROR state until rolled back */
        if ( $this->mTrxLevel ) {
            $ignore = $this->ignoreErrors( true );
            $this->rollback( __METHOD__ );
            $this->ignoreErrors( $ignore );
        }
        parent::reportQueryError( $error, $errno, $sql, $fname, false );
    }

    function queryIgnore( $sql, $fname = __METHOD__ ) {
        return $this->query( $sql, $fname, true );
    }

    function freeResult( $res ) {
        if ( $res instanceof ResultWrapper ) {
            $res = $res->result;
        }
        MediaWiki\suppressWarnings();
        $ok = pg_free_result( $res );
        MediaWiki\restoreWarnings();
        if ( !$ok ) {
            throw new DBUnexpectedError( $this, "Unable to free Postgres result\n" );
        }
    }

    function fetchObject( $res ) {
        if ( $res instanceof ResultWrapper ) {
            $res = $res->result;
        }
        MediaWiki\suppressWarnings();
        $row = pg_fetch_object( $res );
        MediaWiki\restoreWarnings();
        # @todo FIXME: HACK HACK HACK HACK debug

        # @todo hashar: not sure if the following test really trigger if the object
        #          fetching failed.
        $conn = $this->getBindingHandle();
        if ( pg_last_error( $conn ) ) {
            throw new DBUnexpectedError(
                $this,
                'SQL error: ' . htmlspecialchars( pg_last_error( $conn ) )
            );
        }

        return $row;
    }

    function fetchRow( $res ) {
        if ( $res instanceof ResultWrapper ) {
            $res = $res->result;
        }
        MediaWiki\suppressWarnings();
        $row = pg_fetch_array( $res );
        MediaWiki\restoreWarnings();

        $conn = $this->getBindingHandle();
        if ( pg_last_error( $conn ) ) {
            throw new DBUnexpectedError(
                $this,
                'SQL error: ' . htmlspecialchars( pg_last_error( $conn ) )
            );
        }

        return $row;
    }

    function numRows( $res ) {
        if ( $res instanceof ResultWrapper ) {
            $res = $res->result;
        }
        MediaWiki\suppressWarnings();
        $n = pg_num_rows( $res );
        MediaWiki\restoreWarnings();

        $conn = $this->getBindingHandle();
        if ( pg_last_error( $conn ) ) {
            throw new DBUnexpectedError(
                $this,
                'SQL error: ' . htmlspecialchars( pg_last_error( $conn ) )
            );
        }

        return $n;
    }

    function numFields( $res ) {
        if ( $res instanceof ResultWrapper ) {
            $res = $res->result;
        }

        return pg_num_fields( $res );
    }

    function fieldName( $res, $n ) {
        if ( $res instanceof ResultWrapper ) {
            $res = $res->result;
        }

        return pg_field_name( $res, $n );
    }

    function insertId() {
        return $this->mInsertId;
    }

    function dataSeek( $res, $row ) {
        if ( $res instanceof ResultWrapper ) {
            $res = $res->result;
        }

        return pg_result_seek( $res, $row );
    }

    function lastError() {
        if ( $this->mConn ) {
            if ( $this->mLastResult ) {
                return pg_result_error( $this->mLastResult );
            } else {
                return pg_last_error();
            }
        }

        return $this->getLastPHPError() ?: 'No database connection';
    }

    function lastErrno() {
        if ( $this->mLastResult ) {
            return pg_result_error_field( $this->mLastResult, PGSQL_DIAG_SQLSTATE );
        } else {
            return false;
        }
    }

    function affectedRows() {
        if ( !is_null( $this->mAffectedRows ) ) {
            // Forced result for simulated queries
            return $this->mAffectedRows;
        }
        if ( empty( $this->mLastResult ) ) {
            return 0;
        }

        return pg_affected_rows( $this->mLastResult );
    }

    function estimateRowCount( $table, $vars = '*', $conds = '',
        $fname = __METHOD__, $options = []
    ) {
        $options['EXPLAIN'] = true;
        $res = $this->select( $table, $vars, $conds, $fname, $options );
        $rows = -1;
        if ( $res ) {
            $row = $this->fetchRow( $res );
            $count = [];
            if ( preg_match( '/rows=(\d+)/', $row[0], $count ) ) {
                $rows = (int)$count[1];
            }
        }

        return $rows;
    }

    function indexInfo( $table, $index, $fname = __METHOD__ ) {
        $sql = "SELECT indexname FROM pg_indexes WHERE tablename='$table'";
        $res = $this->query( $sql, $fname );
        if ( !$res ) {
            return null;
        }
        foreach ( $res as $row ) {
            if ( $row->indexname == $this->indexName( $index ) ) {
                return $row;
            }
        }

        return false;
    }

    function indexAttributes( $index, $schema = false ) {
        if ( $schema === false ) {
            $schema = $this->getCoreSchema();
        }
        /*
         * A subquery would be not needed if we didn't care about the order
         * of attributes, but we do
         */
        $sql = <<<__INDEXATTR__

            SELECT opcname,
                attname,
                i.indoption[s.g] as option,
                pg_am.amname
            FROM
                (SELECT generate_series(array_lower(isub.indkey,1), array_upper(isub.indkey,1)) AS g
                    FROM
                        pg_index isub
                    JOIN pg_class cis
                        ON cis.oid=isub.indexrelid
                    JOIN pg_namespace ns
                        ON cis.relnamespace = ns.oid
                    WHERE cis.relname='$index' AND ns.nspname='$schema') AS s,
                pg_attribute,
                pg_opclass opcls,
                pg_am,
                pg_class ci
                JOIN pg_index i
                    ON ci.oid=i.indexrelid
                JOIN pg_class ct
                    ON ct.oid = i.indrelid
                JOIN pg_namespace n
                    ON ci.relnamespace = n.oid
                WHERE
                    ci.relname='$index' AND n.nspname='$schema'
                    AND attrelid = ct.oid
                    AND i.indkey[s.g] = attnum
                    AND i.indclass[s.g] = opcls.oid
                    AND pg_am.oid = opcls.opcmethod
__INDEXATTR__;
        $res = $this->query( $sql, __METHOD__ );
        $a = [];
        if ( $res ) {
            foreach ( $res as $row ) {
                $a[] = [
                    $row->attname,
                    $row->opcname,
                    $row->amname,
                    $row->option ];
            }
        } else {
            return null;
        }

        return $a;
    }

    function indexUnique( $table, $index, $fname = __METHOD__ ) {
        $sql = "SELECT indexname FROM pg_indexes WHERE tablename='{$table}'" .
            " AND indexdef LIKE 'CREATE UNIQUE%(" .
            $this->strencode( $this->indexName( $index ) ) .
            ")'";
        $res = $this->query( $sql, $fname );
        if ( !$res ) {
            return null;
        }

        return $res->numRows() > 0;
    }

    function selectSQLText(
        $table, $vars, $conds = '', $fname = __METHOD__, $options = [], $join_conds = []
    ) {
        // Change the FOR UPDATE option as necessary based on the join conditions. Then pass
        // to the parent function to get the actual SQL text.
        // In Postgres when using FOR UPDATE, only the main table and tables that are inner joined
        // can be locked. That means tables in an outer join cannot be FOR UPDATE locked. Trying to
        // do so causes a DB error. This wrapper checks which tables can be locked and adjusts it
        // accordingly.
        // MySQL uses "ORDER BY NULL" as an optimization hint, but that is illegal in PostgreSQL.
        if ( is_array( $options ) ) {
            $forUpdateKey = array_search( 'FOR UPDATE', $options, true );
            if ( $forUpdateKey !== false && $join_conds ) {
                unset( $options[$forUpdateKey] );

                foreach ( $join_conds as $table_cond => $join_cond ) {
                    if ( 0 === preg_match( '/^(?:LEFT|RIGHT|FULL)(?: OUTER)? JOIN$/i', $join_cond[0] ) ) {
                        $options['FOR UPDATE'][] = $table_cond;
                    }
                }
            }

            if ( isset( $options['ORDER BY'] ) && $options['ORDER BY'] == 'NULL' ) {
                unset( $options['ORDER BY'] );
            }
        }

        return parent::selectSQLText( $table, $vars, $conds, $fname, $options, $join_conds );
    }

    function insert( $table, $args, $fname = __METHOD__, $options = [] ) {
        if ( !count( $args ) ) {
            return true;
        }

        $table = $this->tableName( $table );
        if ( !isset( $this->numericVersion ) ) {
            $this->getServerVersion();
        }

        if ( !is_array( $options ) ) {
            $options = [ $options ];
        }

        if ( isset( $args[0] ) && is_array( $args[0] ) ) {
            $multi = true;
            $keys = array_keys( $args[0] );
        } else {
            $multi = false;
            $keys = array_keys( $args );
        }

        // If IGNORE is set, we use savepoints to emulate mysql's behavior
        $savepoint = $olde = null;
        $numrowsinserted = 0;
        if ( in_array( 'IGNORE', $options ) ) {
            $savepoint = new SavepointPostgres( $this, 'mw', $this->queryLogger );
            $olde = error_reporting( 0 );
            // For future use, we may want to track the number of actual inserts
            // Right now, insert (all writes) simply return true/false
        }

        $sql = "INSERT INTO $table (" . implode( ',', $keys ) . ') VALUES ';

        if ( $multi ) {
            if ( $this->numericVersion >= 8.2 && !$savepoint ) {
                $first = true;
                foreach ( $args as $row ) {
                    if ( $first ) {
                        $first = false;
                    } else {
                        $sql .= ',';
                    }
                    $sql .= '(' . $this->makeList( $row ) . ')';
                }
                $res = (bool)$this->query( $sql, $fname, $savepoint );
            } else {
                $res = true;
                $origsql = $sql;
                foreach ( $args as $row ) {
                    $tempsql = $origsql;
                    $tempsql .= '(' . $this->makeList( $row ) . ')';

                    if ( $savepoint ) {
                        $savepoint->savepoint();
                    }

                    $tempres = (bool)$this->query( $tempsql, $fname, $savepoint );

                    if ( $savepoint ) {
                        $bar = pg_result_error( $this->mLastResult );
                        if ( $bar != false ) {
                            $savepoint->rollback();
                        } else {
                            $savepoint->release();
                            $numrowsinserted++;
                        }
                    }

                    // If any of them fail, we fail overall for this function call
                    // Note that this will be ignored if IGNORE is set
                    if ( !$tempres ) {
                        $res = false;
                    }
                }
            }
        } else {
            // Not multi, just a lone insert
            if ( $savepoint ) {
                $savepoint->savepoint();
            }

            $sql .= '(' . $this->makeList( $args ) . ')';
            $res = (bool)$this->query( $sql, $fname, $savepoint );
            if ( $savepoint ) {
                $bar = pg_result_error( $this->mLastResult );
                if ( $bar != false ) {
                    $savepoint->rollback();
                } else {
                    $savepoint->release();
                    $numrowsinserted++;
                }
            }
        }
        if ( $savepoint ) {
            error_reporting( $olde );
            $savepoint->commit();

            // Set the affected row count for the whole operation
            $this->mAffectedRows = $numrowsinserted;

            // IGNORE always returns true
            return true;
        }

        return $res;
    }

    function nativeInsertSelect( $destTable, $srcTable, $varMap, $conds, $fname = __METHOD__,
        $insertOptions = [], $selectOptions = [] ) {
        $destTable = $this->tableName( $destTable );

        if ( !is_array( $insertOptions ) ) {
            $insertOptions = [ $insertOptions ];
        }

        /*
         * If IGNORE is set, we use savepoints to emulate mysql's behavior
         * Ignore LOW PRIORITY option, since it is MySQL-specific
         */
        $savepoint = $olde = null;
        $numrowsinserted = 0;
        if ( in_array( 'IGNORE', $insertOptions ) ) {
            $savepoint = new SavepointPostgres( $this, 'mw', $this->queryLogger );
            $olde = error_reporting( 0 );
            $savepoint->savepoint();
        }

        if ( !is_array( $selectOptions ) ) {
            $selectOptions = [ $selectOptions ];
        }
        list( $startOpts, $useIndex, $tailOpts, $ignoreIndex ) =
            $this->makeSelectOptions( $selectOptions );
        if ( is_array( $srcTable ) ) {
            $srcTable = implode( ',', array_map( [ &$this, 'tableName' ], $srcTable ) );
        } else {
            $srcTable = $this->tableName( $srcTable );
        }

        $sql = "INSERT INTO $destTable (" . implode( ',', array_keys( $varMap ) ) . ')' .
            " SELECT $startOpts " . implode( ',', $varMap ) .
            " FROM $srcTable $useIndex $ignoreIndex ";

        if ( $conds != '*' ) {
            $sql .= ' WHERE ' . $this->makeList( $conds, LIST_AND );
        }

        $sql .= " $tailOpts";

        $res = (bool)$this->query( $sql, $fname, $savepoint );
        if ( $savepoint ) {
            $bar = pg_result_error( $this->mLastResult );
            if ( $bar != false ) {
                $savepoint->rollback();
            } else {
                $savepoint->release();
                $numrowsinserted++;
            }
            error_reporting( $olde );
            $savepoint->commit();

            // Set the affected row count for the whole operation
            $this->mAffectedRows = $numrowsinserted;

            // IGNORE always returns true
            return true;
        }

        return $res;
    }

    function tableName( $name, $format = 'quoted' ) {
        // Replace reserved words with better ones
        $name = $this->remappedTableName( $name );

        return parent::tableName( $name, $format );
    }

    public function remappedTableName( $name ) {
        if ( $name === 'user' ) {
            return 'mwuser';
        } elseif ( $name === 'text' ) {
            return 'pagecontent';
        }

        return $name;
    }

    public function realTableName( $name, $format = 'quoted' ) {
        return parent::tableName( $name, $format );
    }

    function nextSequenceValue( $seqName ) {
        $safeseq = str_replace( "'", "''", $seqName );
        $res = $this->query( "SELECT nextval('$safeseq')" );
        $row = $this->fetchRow( $res );
        $this->mInsertId = $row[0];

        return $this->mInsertId;
    }

    function currentSequenceValue( $seqName ) {
        $safeseq = str_replace( "'", "''", $seqName );
        $res = $this->query( "SELECT currval('$safeseq')" );
        $row = $this->fetchRow( $res );
        $currval = $row[0];

        return $currval;
    }

    # Returns the size of a text field, or -1 for "unlimited"
    function textFieldSize( $table, $field ) {
        $table = $this->tableName( $table );
        $sql = "SELECT t.typname as ftype,a.atttypmod as size
            FROM pg_class c, pg_attribute a, pg_type t
            WHERE relname='$table' AND a.attrelid=c.oid AND
                a.atttypid=t.oid and a.attname='$field'";
        $res = $this->query( $sql );
        $row = $this->fetchObject( $res );
        if ( $row->ftype == 'varchar' ) {
            $size = $row->size - 4;
        } else {
            $size = $row->size;
        }

        return $size;
    }

    function limitResult( $sql, $limit, $offset = false ) {
        return "$sql LIMIT $limit " . ( is_numeric( $offset ) ? " OFFSET {$offset} " : '' );
    }

    function wasDeadlock() {
        return $this->lastErrno() == '40P01';
    }

    function duplicateTableStructure(
        $oldName, $newName, $temporary = false, $fname = __METHOD__
    ) {
        $newName = $this->addIdentifierQuotes( $newName );
        $oldName = $this->addIdentifierQuotes( $oldName );

        return $this->query( 'CREATE ' . ( $temporary ? 'TEMPORARY ' : '' ) . " TABLE $newName " .
            "(LIKE $oldName INCLUDING DEFAULTS)", $fname );
    }

    function listTables( $prefix = null, $fname = __METHOD__ ) {
        $eschema = $this->addQuotes( $this->getCoreSchema() );
        $result = $this->query(
            "SELECT tablename FROM pg_tables WHERE schemaname = $eschema", $fname );
        $endArray = [];

        foreach ( $result as $table ) {
            $vars = get_object_vars( $table );
            $table = array_pop( $vars );
            if ( !$prefix || strpos( $table, $prefix ) === 0 ) {
                $endArray[] = $table;
            }
        }

        return $endArray;
    }

    function timestamp( $ts = 0 ) {
        $ct = new ConvertibleTimestamp( $ts );

        return $ct->getTimestamp( TS_POSTGRES );
    }

    function pg_array_parse( $text, &$output, $limit = false, $offset = 1 ) {
        if ( false === $limit ) {
            $limit = strlen( $text ) - 1;
            $output = [];
        }
        if ( '{}' == $text ) {
            return $output;
        }
        do {
            if ( '{' != $text[$offset] ) {
                preg_match( "/(\\{?\"([^\"\\\\]|\\\\.)*\"|[^,{}]+)+([,}]+)/",
                    $text, $match, 0, $offset );
                $offset += strlen( $match[0] );
                $output[] = ( '"' != $match[1][0]
                    ? $match[1]
                    : stripcslashes( substr( $match[1], 1, -1 ) ) );
                if ( '},' == $match[3] ) {
                    return $output;
                }
            } else {
                $offset = $this->pg_array_parse( $text, $output, $limit, $offset + 1 );
            }
        } while ( $limit > $offset );

        return $output;
    }

    public function aggregateValue( $valuedata, $valuename = 'value' ) {
        return $valuedata;
    }

    public function getSoftwareLink() {
        return '[{{int:version-db-postgres-url}} PostgreSQL]';
    }

    function getCurrentSchema() {
        $res = $this->query( "SELECT current_schema()", __METHOD__ );
        $row = $this->fetchRow( $res );

        return $row[0];
    }

    function getSchemas() {
        $res = $this->query( "SELECT current_schemas(false)", __METHOD__ );
        $row = $this->fetchRow( $res );
        $schemas = [];

        /* PHP pgsql support does not support array type, "{a,b}" string is returned */

        return $this->pg_array_parse( $row[0], $schemas );
    }

    function getSearchPath() {
        $res = $this->query( "SHOW search_path", __METHOD__ );
        $row = $this->fetchRow( $res );

        /* PostgreSQL returns SHOW values as strings */

        return explode( ",", $row[0] );
    }

    function setSearchPath( $search_path ) {
        $this->query( "SET search_path = " . implode( ", ", $search_path ) );
    }

    function determineCoreSchema( $desiredSchema ) {
        $this->begin( __METHOD__, self::TRANSACTION_INTERNAL );
        if ( $this->schemaExists( $desiredSchema ) ) {
            if ( in_array( $desiredSchema, $this->getSchemas() ) ) {
                $this->mCoreSchema = $desiredSchema;
                $this->queryLogger->debug(
                    "Schema \"" . $desiredSchema . "\" already in the search path\n" );
            } else {
                $search_path = $this->getSearchPath();
                array_unshift( $search_path,
                    $this->addIdentifierQuotes( $desiredSchema ) );
                $this->setSearchPath( $search_path );
                $this->mCoreSchema = $desiredSchema;
                $this->queryLogger->debug(
                    "Schema \"" . $desiredSchema . "\" added to the search path\n" );
            }
        } else {
            $this->mCoreSchema = $this->getCurrentSchema();
            $this->queryLogger->debug(
                "Schema \"" . $desiredSchema . "\" not found, using current \"" .
                $this->mCoreSchema . "\"\n" );
        }
        /* Commit SET otherwise it will be rollbacked on error or IGNORE SELECT */
        $this->commit( __METHOD__, self::FLUSHING_INTERNAL );
    }

    function getCoreSchema() {
        return $this->mCoreSchema;
    }

    function getServerVersion() {
        if ( !isset( $this->numericVersion ) ) {
            $conn = $this->getBindingHandle();
            $versionInfo = pg_version( $conn );
            if ( version_compare( $versionInfo['client'], '7.4.0', 'lt' ) ) {
                // Old client, abort install
                $this->numericVersion = '7.3 or earlier';
            } elseif ( isset( $versionInfo['server'] ) ) {
                // Normal client
                $this->numericVersion = $versionInfo['server'];
            } else {
                // Bug 16937: broken pgsql extension from PHP<5.3
                $this->numericVersion = pg_parameter_status( $conn, 'server_version' );
            }
        }

        return $this->numericVersion;
    }

    function relationExists( $table, $types, $schema = false ) {
        if ( !is_array( $types ) ) {
            $types = [ $types ];
        }
        if ( $schema === false ) {
            $schema = $this->getCoreSchema();
        }
        $etable = $this->addQuotes( $table );
        $eschema = $this->addQuotes( $schema );
        $sql = "SELECT 1 FROM pg_catalog.pg_class c, pg_catalog.pg_namespace n "
            . "WHERE c.relnamespace = n.oid AND c.relname = $etable AND n.nspname = $eschema "
            . "AND c.relkind IN ('" . implode( "','", $types ) . "')";
        $res = $this->query( $sql );
        $count = $res ? $res->numRows() : 0;

        return (bool)$count;
    }

    function tableExists( $table, $fname = __METHOD__, $schema = false ) {
        return $this->relationExists( $table, [ 'r', 'v' ], $schema );
    }

    function sequenceExists( $sequence, $schema = false ) {
        return $this->relationExists( $sequence, 'S', $schema );
    }

    function triggerExists( $table, $trigger ) {
        $q = <<<SQL
    SELECT 1 FROM pg_class, pg_namespace, pg_trigger
        WHERE relnamespace=pg_namespace.oid AND relkind='r'
              AND tgrelid=pg_class.oid
              AND nspname=%s AND relname=%s AND tgname=%s
SQL;
        $res = $this->query(
            sprintf(
                $q,
                $this->addQuotes( $this->getCoreSchema() ),
                $this->addQuotes( $table ),
                $this->addQuotes( $trigger )
            )
        );
        if ( !$res ) {
            return null;
        }
        $rows = $res->numRows();

        return $rows;
    }

    function ruleExists( $table, $rule ) {
        $exists = $this->selectField( 'pg_rules', 'rulename',
            [
                'rulename' => $rule,
                'tablename' => $table,
                'schemaname' => $this->getCoreSchema()
            ]
        );

        return $exists === $rule;
    }

    function constraintExists( $table, $constraint ) {
        $sql = sprintf( "SELECT 1 FROM information_schema.table_constraints " .
            "WHERE constraint_schema = %s AND table_name = %s AND constraint_name = %s",
            $this->addQuotes( $this->getCoreSchema() ),
            $this->addQuotes( $table ),
            $this->addQuotes( $constraint )
        );
        $res = $this->query( $sql );
        if ( !$res ) {
            return null;
        }
        $rows = $res->numRows();

        return $rows;
    }

    function schemaExists( $schema ) {
        $exists = $this->selectField( '"pg_catalog"."pg_namespace"', 1,
            [ 'nspname' => $schema ], __METHOD__ );

        return (bool)$exists;
    }

    function roleExists( $roleName ) {
        $exists = $this->selectField( '"pg_catalog"."pg_roles"', 1,
            [ 'rolname' => $roleName ], __METHOD__ );

        return (bool)$exists;
    }

    function fieldInfo( $table, $field ) {
        return PostgresField::fromText( $this, $table, $field );
    }

    function fieldType( $res, $index ) {
        if ( $res instanceof ResultWrapper ) {
            $res = $res->result;
        }

        return pg_field_type( $res, $index );
    }

    function encodeBlob( $b ) {
        return new PostgresBlob( pg_escape_bytea( $b ) );
    }

    function decodeBlob( $b ) {
        if ( $b instanceof PostgresBlob ) {
            $b = $b->fetch();
        } elseif ( $b instanceof Blob ) {
            return $b->fetch();
        }

        return pg_unescape_bytea( $b );
    }

    function strencode( $s ) {
        // Should not be called by us
        return pg_escape_string( $this->getBindingHandle(), $s );
    }

    function addQuotes( $s ) {
        $conn = $this->getBindingHandle();

        if ( is_null( $s ) ) {
            return 'NULL';
        } elseif ( is_bool( $s ) ) {
            return intval( $s );
        } elseif ( $s instanceof Blob ) {
            if ( $s instanceof PostgresBlob ) {
                $s = $s->fetch();
            } else {
                $s = pg_escape_bytea( $conn, $s->fetch() );
            }
            return "'$s'";
        }

        return "'" . pg_escape_string( $conn, $s ) . "'";
    }

    protected function replaceVars( $ins ) {
        $ins = parent::replaceVars( $ins );

        if ( $this->numericVersion >= 8.3 ) {
            // Thanks for not providing backwards-compatibility, 8.3
            $ins = preg_replace( "/to_tsvector\s*\(\s*'default'\s*,/", 'to_tsvector(', $ins );
        }

        if ( $this->numericVersion <= 8.1 ) { // Our minimum version
            $ins = str_replace( 'USING gin', 'USING gist', $ins );
        }

        return $ins;
    }

    function makeSelectOptions( $options ) {
        $preLimitTail = $postLimitTail = '';
        $startOpts = $useIndex = $ignoreIndex = '';

        $noKeyOptions = [];
        foreach ( $options as $key => $option ) {
            if ( is_numeric( $key ) ) {
                $noKeyOptions[$option] = true;
            }
        }

        $preLimitTail .= $this->makeGroupByWithHaving( $options );

        $preLimitTail .= $this->makeOrderBy( $options );

        // if ( isset( $options['LIMIT'] ) ) {
        //  $tailOpts .= $this->limitResult( '', $options['LIMIT'],
        //      isset( $options['OFFSET'] ) ? $options['OFFSET']
        //      : false );
        // }

        if ( isset( $options['FOR UPDATE'] ) ) {
            $postLimitTail .= ' FOR UPDATE OF ' .
                implode( ', ', array_map( [ &$this, 'tableName' ], $options['FOR UPDATE'] ) );
        } elseif ( isset( $noKeyOptions['FOR UPDATE'] ) ) {
            $postLimitTail .= ' FOR UPDATE';
        }

        if ( isset( $noKeyOptions['DISTINCT'] ) || isset( $noKeyOptions['DISTINCTROW'] ) ) {
            $startOpts .= 'DISTINCT';
        }

        return [ $startOpts, $useIndex, $preLimitTail, $postLimitTail, $ignoreIndex ];
    }

    function getDBname() {
        return $this->mDBname;
    }

    function getServer() {
        return $this->mServer;
    }

    function buildConcat( $stringList ) {
        return implode( ' || ', $stringList );
    }

    public function buildGroupConcatField(
        $delimiter, $table, $field, $conds = '', $options = [], $join_conds = []
    ) {
        $fld = "array_to_string(array_agg($field)," . $this->addQuotes( $delimiter ) . ')';

        return '(' . $this->selectSQLText( $table, $fld, $conds, null, [], $join_conds ) . ')';
    }

    public function buildStringCast( $field ) {
        return $field . '::text';
    }

    public function streamStatementEnd( &$sql, &$newLine ) {
        # Allow dollar quoting for function declarations
        if ( substr( $newLine, 0, 4 ) == '$mw$' ) {
            if ( $this->delimiter ) {
                $this->delimiter = false;
            } else {
                $this->delimiter = ';';
            }
        }

        return parent::streamStatementEnd( $sql, $newLine );
    }

    public function lockIsFree( $lockName, $method ) {
        $key = $this->addQuotes( $this->bigintFromLockName( $lockName ) );
        $result = $this->query( "SELECT (CASE(pg_try_advisory_lock($key))
            WHEN 'f' THEN 'f' ELSE pg_advisory_unlock($key) END) AS lockstatus", $method );
        $row = $this->fetchObject( $result );

        return ( $row->lockstatus === 't' );
    }

    public function lock( $lockName, $method, $timeout = 5 ) {
        $key = $this->addQuotes( $this->bigintFromLockName( $lockName ) );
        $loop = new WaitConditionLoop(
            function () use ( $lockName, $key, $timeout, $method ) {
                $res = $this->query( "SELECT pg_try_advisory_lock($key) AS lockstatus", $method );
                $row = $this->fetchObject( $res );
                if ( $row->lockstatus === 't' ) {
                    parent::lock( $lockName, $method, $timeout ); // record
                    return true;
                }

                return WaitConditionLoop::CONDITION_CONTINUE;
            },
            $timeout
        );

        return ( $loop->invoke() === $loop::CONDITION_REACHED );
    }

    public function unlock( $lockName, $method ) {
        $key = $this->addQuotes( $this->bigintFromLockName( $lockName ) );
        $result = $this->query( "SELECT pg_advisory_unlock($key) as lockstatus", $method );
        $row = $this->fetchObject( $result );

        if ( $row->lockstatus === 't' ) {
            parent::unlock( $lockName, $method ); // record
            return true;
        }

        $this->queryLogger->debug( __METHOD__ . " failed to release lock\n" );

        return false;
    }

    private function bigintFromLockName( $lockName ) {
        return Wikimedia\base_convert( substr( sha1( $lockName ), 0, 15 ), 16, 10 );
    }
}