DatabasePostgres.php

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<?php
namespace Wikimedia\Rdbms;
 
use RuntimeException;
use Wikimedia\Timestamp\ConvertibleTimestamp;
use Wikimedia\WaitConditionLoop;
 
class DatabasePostgres extends Database {
    private $port;
    private $coreSchema;
    private $tempSchema;
    private $keywordTableMap;
    private $numericVersion;
 
    private $lastResultHandle;
 
    public function __construct( array $params ) {
        $this->port = intval( $params['port'] ?? null );
 
        if ( isset( $params['keywordTableMap'] ) ) {
            wfDeprecatedMsg( 'Passing keywordTableMap parameter to ' .
                'DatabasePostgres::__construct() is deprecated', '1.37'
            );
 
            $this->keywordTableMap = $params['keywordTableMap'];
        }
 
        parent::__construct( $params );
    }
 
    public function getType() {
        return 'postgres';
    }
 
    public function implicitOrderby() {
        return false;
    }
 
    protected function open( $server, $user, $password, $db, $schema, $tablePrefix ) {
        if ( !function_exists( 'pg_connect' ) ) {
            throw $this->newExceptionAfterConnectError(
                "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)"
            );
        }
 
        $this->close( __METHOD__ );
 
        $connectVars = [
            // A database must be specified in order to connect to Postgres. If $dbName is not
            // specified, then use the standard "postgres" database that should exist by default.
            'dbname' => strlen( $db ) ? $db : 'postgres',
            'user' => $user,
            'password' => $password
        ];
        if ( strlen( $server ) ) {
            $connectVars['host'] = $server;
        }
        if ( $this->port > 0 ) {
            $connectVars['port'] = $this->port;
        }
        if ( $this->getFlag( self::DBO_SSL ) ) {
            $connectVars['sslmode'] = 'require';
        }
        $connectString = $this->makeConnectionString( $connectVars );
 
        $this->installErrorHandler();
        try {
            $this->conn = pg_connect( $connectString, PGSQL_CONNECT_FORCE_NEW ) ?: null;
        } catch ( RuntimeException $e ) {
            $this->restoreErrorHandler();
            throw $this->newExceptionAfterConnectError( $e->getMessage() );
        }
        $error = $this->restoreErrorHandler();
 
        if ( !$this->conn ) {
            throw $this->newExceptionAfterConnectError( $error ?: $this->lastError() );
        }
 
        try {
            // Since no transaction is active at this point, any SET commands should apply
            // for the entire session (e.g. will not be reverted on transaction rollback).
            // See https://www.postgresql.org/docs/8.3/sql-set.html
            $variables = [
                'client_encoding' => 'UTF8',
                'datestyle' => 'ISO, YMD',
                'timezone' => 'GMT',
                'standard_conforming_strings' => 'on',
                'bytea_output' => 'escape',
                'client_min_messages' => 'ERROR'
            ];
            foreach ( $variables as $var => $val ) {
                $this->query(
                    'SET ' . $this->addIdentifierQuotes( $var ) . ' = ' . $this->addQuotes( $val ),
                    __METHOD__,
                    self::QUERY_IGNORE_DBO_TRX | self::QUERY_NO_RETRY | self::QUERY_CHANGE_TRX
                );
            }
            $this->determineCoreSchema( $schema );
            $this->currentDomain = new DatabaseDomain( $db, $schema, $tablePrefix );
        } catch ( RuntimeException $e ) {
            throw $this->newExceptionAfterConnectError( $e->getMessage() );
        }
    }
 
    protected function relationSchemaQualifier() {
        if ( $this->coreSchema === $this->currentDomain->getSchema() ) {
            // The schema to be used is now in the search path; no need for explicit qualification
            return '';
        }
 
        return parent::relationSchemaQualifier();
    }
 
    public function databasesAreIndependent() {
        return true;
    }
 
    public function doSelectDomain( DatabaseDomain $domain ) {
        if ( $this->getDBname() !== $domain->getDatabase() ) {
            // Postgres doesn't support selectDB in the same way MySQL does.
            // So if the DB name doesn't match the open connection, open a new one
            $this->open(
                $this->connectionParams[self::CONN_HOST],
                $this->connectionParams[self::CONN_USER],
                $this->connectionParams[self::CONN_PASSWORD],
                $domain->getDatabase(),
                $domain->getSchema(),
                $domain->getTablePrefix()
            );
        } else {
            $this->currentDomain = $domain;
        }
 
        return true;
    }
 
    private function makeConnectionString( $vars ) {
        $s = '';
        foreach ( $vars as $name => $value ) {
            $s .= "$name='" . str_replace( "'", "\\'", $value ) . "' ";
        }
 
        return $s;
    }
 
    protected function closeConnection() {
        return $this->conn ? pg_close( $this->conn ) : true;
    }
 
    protected function isTransactableQuery( $sql ) {
        return parent::isTransactableQuery( $sql ) &&
            !preg_match( '/^SELECT\s+pg_(try_|)advisory_\w+\‍(/', $sql );
    }
 
    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->lastResultHandle = pg_get_result( $conn );
        if ( pg_result_error( $this->lastResultHandle ) ) {
            return false;
        }
 
        return $this->lastResultHandle ?
            new PostgresResultWrapper( $this, $this->getBindingHandle(), $this->lastResultHandle ) : false;
    }
 
    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",
                $d, pg_result_error_field( $this->lastResultHandle, $d ) ) );
        }
    }
 
    public function insertId() {
        $res = $this->query(
            "SELECT lastval()",
            __METHOD__,
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE
        );
        $row = $this->fetchRow( $res );
 
        return $row[0] === null ? null : (int)$row[0];
    }
 
    public function lastError() {
        if ( $this->conn ) {
            if ( $this->lastResultHandle ) {
                return pg_result_error( $this->lastResultHandle );
            } else {
                return pg_last_error();
            }
        }
 
        return $this->getLastPHPError() ?: 'No database connection';
    }
 
    public function lastErrno() {
        if ( $this->lastResultHandle ) {
            return pg_result_error_field( $this->lastResultHandle, PGSQL_DIAG_SQLSTATE );
        } else {
            return false;
        }
    }
 
    protected function fetchAffectedRowCount() {
        if ( !$this->lastResultHandle ) {
            return 0;
        }
 
        return pg_affected_rows( $this->lastResultHandle );
    }
 
    public function estimateRowCount( $table, $var = '*', $conds = '',
        $fname = __METHOD__, $options = [], $join_conds = []
    ) {
        $conds = $this->normalizeConditions( $conds, $fname );
        $column = $this->extractSingleFieldFromList( $var );
        if ( is_string( $column ) && !in_array( $column, [ '*', '1' ] ) ) {
            $conds[] = "$column IS NOT NULL";
        }
 
        $options['EXPLAIN'] = true;
        $res = $this->select( $table, $var, $conds, $fname, $options, $join_conds );
        $rows = -1;
        if ( $res ) {
            $row = $this->fetchRow( $res );
            $count = [];
            if ( preg_match( '/rows=(\d+)/', $row[0], $count ) ) {
                $rows = (int)$count[1];
            }
        }
 
        return $rows;
    }
 
    public function indexInfo( $table, $index, $fname = __METHOD__ ) {
        $res = $this->query(
            "SELECT indexname FROM pg_indexes WHERE tablename='$table'",
            $fname,
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE
        );
        if ( !$res ) {
            return null;
        }
        foreach ( $res as $row ) {
            if ( $row->indexname == $this->indexName( $index ) ) {
                return $row;
            }
        }
 
        return false;
    }
 
    public function indexAttributes( $index, $schema = false ) {
        if ( $schema === false ) {
            $schemas = $this->getCoreSchemas();
        } else {
            $schemas = [ $schema ];
        }
 
        $eindex = $this->addQuotes( $index );
 
        $flags = self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE;
        foreach ( $schemas as $schema ) {
            $eschema = $this->addQuotes( $schema );
            /*
             * 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=$eindex AND ns.nspname=$eschema) 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=$eindex AND n.nspname=$eschema
                        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__, $flags );
            $a = [];
            if ( $res ) {
                foreach ( $res as $row ) {
                    $a[] = [
                        $row->attname,
                        $row->opcname,
                        $row->amname,
                        $row->option ];
                }
                return $a;
            }
        }
        return null;
    }
 
    public function indexUnique( $table, $index, $fname = __METHOD__ ) {
        $flags = self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE;
        $sql = "SELECT indexname FROM pg_indexes WHERE tablename='{$table}'" .
            " AND indexdef LIKE 'CREATE UNIQUE%(" .
            $this->strencode( $this->indexName( $index ) ) .
            ")'";
        $res = $this->query( $sql, $fname, $flags );
        if ( !$res ) {
            return null;
        }
 
        return $res->numRows() > 0;
    }
 
    public function selectSQLText(
        $table, $vars, $conds = '', $fname = __METHOD__, $options = [], $join_conds = []
    ) {
        if ( is_string( $options ) ) {
            $options = [ $options ];
        }
 
        // 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] );
                $options['FOR UPDATE'] = [];
 
                $toCheck = $table;
                reset( $toCheck );
                while ( $toCheck ) {
                    $alias = key( $toCheck );
                    $name = $toCheck[$alias];
                    unset( $toCheck[$alias] );
 
                    $hasAlias = !is_numeric( $alias );
                    if ( !$hasAlias && is_string( $name ) ) {
                        $alias = $name;
                    }
 
                    if ( !isset( $join_conds[$alias] ) ||
                        !preg_match( '/^(?:LEFT|RIGHT|FULL)(?: OUTER)? JOIN$/i', $join_conds[$alias][0] )
                    ) {
                        if ( is_array( $name ) ) {
                            // It's a parenthesized group, process all the tables inside the group.
                            $toCheck = array_merge( $toCheck, $name );
                        } else {
                            // Quote alias names so $this->tableName() won't mangle them
                            $options['FOR UPDATE'][] = $hasAlias ? $this->addIdentifierQuotes( $alias ) : $alias;
                        }
                    }
                }
            }
 
            if ( isset( $options['ORDER BY'] ) && $options['ORDER BY'] == 'NULL' ) {
                unset( $options['ORDER BY'] );
            }
        }
 
        return parent::selectSQLText( $table, $vars, $conds, $fname, $options, $join_conds );
    }
 
    protected function makeInsertNonConflictingVerbAndOptions() {
        return [ 'INSERT INTO', 'ON CONFLICT DO NOTHING' ];
    }
 
    public function doInsertNonConflicting( $table, array $rows, $fname ) {
        // Postgres 9.5 supports "ON CONFLICT"
        if ( $this->getServerVersion() >= 9.5 ) {
            parent::doInsertNonConflicting( $table, $rows, $fname );
 
            return;
        }
 
        $affectedRowCount = 0;
        // Emulate INSERT IGNORE via savepoints/rollback
        $tok = $this->startAtomic( "$fname (outer)", self::ATOMIC_CANCELABLE );
        try {
            $encTable = $this->tableName( $table );
            foreach ( $rows as $row ) {
                list( $sqlColumns, $sqlTuples ) = $this->makeInsertLists( [ $row ] );
                $tempsql = "INSERT INTO $encTable ($sqlColumns) VALUES $sqlTuples";
 
                $this->startAtomic( "$fname (inner)", self::ATOMIC_CANCELABLE );
                try {
                    $this->query( $tempsql, $fname, self::QUERY_CHANGE_ROWS );
                    $this->endAtomic( "$fname (inner)" );
                    $affectedRowCount++;
                } catch ( DBQueryError $e ) {
                    $this->cancelAtomic( "$fname (inner)" );
                    // Our IGNORE is supposed to ignore duplicate key errors, but not others.
                    // (even though MySQL's version apparently ignores all errors)
                    if ( $e->errno !== '23505' ) {
                        throw $e;
                    }
                }
            }
        } catch ( RuntimeException $e ) {
            $this->cancelAtomic( "$fname (outer)", $tok );
            throw $e;
        }
        $this->endAtomic( "$fname (outer)" );
        // Set the affected row count for the whole operation
        $this->affectedRowCount = $affectedRowCount;
    }
 
    protected function makeUpdateOptionsArray( $options ) {
        $options = $this->normalizeOptions( $options );
        // PostgreSQL doesn't support anything like "ignore" for UPDATE.
        $options = array_diff( $options, [ 'IGNORE' ] );
 
        return parent::makeUpdateOptionsArray( $options );
    }
 
    protected function doInsertSelectNative(
        $destTable,
        $srcTable,
        array $varMap,
        $conds,
        $fname,
        array $insertOptions,
        array $selectOptions,
        $selectJoinConds
    ) {
        if ( in_array( 'IGNORE', $insertOptions ) ) {
            if ( $this->getServerVersion() >= 9.5 ) {
                // Use "ON CONFLICT DO" if we have it for IGNORE
                $destTable = $this->tableName( $destTable );
 
                $selectSql = $this->selectSQLText(
                    $srcTable,
                    array_values( $varMap ),
                    $conds,
                    $fname,
                    $selectOptions,
                    $selectJoinConds
                );
 
                $sql = "INSERT INTO $destTable (" . implode( ',', array_keys( $varMap ) ) . ') ' .
                    $selectSql . ' ON CONFLICT DO NOTHING';
 
                $this->query( $sql, $fname, self::QUERY_CHANGE_ROWS );
            } else {
                // IGNORE and we don't have ON CONFLICT DO NOTHING, so just use the non-native version
                $this->doInsertSelectGeneric(
                    $destTable, $srcTable, $varMap, $conds, $fname,
                    $insertOptions, $selectOptions, $selectJoinConds
                );
            }
        } else {
            parent::doInsertSelectNative( $destTable, $srcTable, $varMap, $conds, $fname,
                $insertOptions, $selectOptions, $selectJoinConds );
        }
    }
 
    public function tableName( $name, $format = 'quoted' ) {
        return parent::tableName( $name, $format );
    }
 
    public function remappedTableName( $name ) {
        wfDeprecated( __METHOD__, '1.37' );
 
        return $this->keywordTableMap[$name] ?? $name;
    }
 
    public function realTableName( $name, $format = 'quoted' ) {
        return parent::tableName( $name, $format );
    }
 
    public function nextSequenceValue( $seqName ) {
        return new NextSequenceValue;
    }
 
    public function currentSequenceValue( $seqName ) {
        $res = $this->query(
            "SELECT currval('" . str_replace( "'", "''", $seqName ) . "')",
            __METHOD__,
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE
        );
        $row = $this->fetchRow( $res );
        $currval = $row[0];
 
        return $currval;
    }
 
    public function textFieldSize( $table, $field ) {
        $flags = self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE;
        $encTable = $this->tableName( $table );
        $sql = "SELECT t.typname as ftype,a.atttypmod as size
            FROM pg_class c, pg_attribute a, pg_type t
            WHERE relname='$encTable' AND a.attrelid=c.oid AND
                a.atttypid=t.oid and a.attname='$field'";
        $res = $this->query( $sql, __METHOD__, $flags );
        $row = $this->fetchObject( $res );
        if ( $row->ftype == 'varchar' ) {
            $size = $row->size - 4;
        } else {
            $size = $row->size;
        }
 
        return $size;
    }
 
    public function limitResult( $sql, $limit, $offset = false ) {
        return "$sql LIMIT $limit " . ( is_numeric( $offset ) ? " OFFSET {$offset} " : '' );
    }
 
    public function wasDeadlock() {
        // https://www.postgresql.org/docs/9.2/static/errcodes-appendix.html
        return $this->lastErrno() === '40P01';
    }
 
    public function wasLockTimeout() {
        // https://www.postgresql.org/docs/9.2/static/errcodes-appendix.html
        return $this->lastErrno() === '55P03';
    }
 
    public function wasConnectionError( $errno ) {
        // https://www.postgresql.org/docs/9.2/static/errcodes-appendix.html
        static $codes = [ '08000', '08003', '08006', '08001', '08004', '57P01', '57P03', '53300' ];
 
        return in_array( $errno, $codes, true );
    }
 
    protected function wasKnownStatementRollbackError() {
        return false; // transaction has to be rolled-back from error state
    }
 
    public function duplicateTableStructure(
        $oldName, $newName, $temporary = false, $fname = __METHOD__
    ) {
        $newNameE = $this->addIdentifierQuotes( $newName );
        $oldNameE = $this->addIdentifierQuotes( $oldName );
 
        $temporary = $temporary ? 'TEMPORARY' : '';
 
        $ret = $this->query(
            "CREATE $temporary TABLE $newNameE " .
                "(LIKE $oldNameE INCLUDING DEFAULTS INCLUDING INDEXES)",
            $fname,
            self::QUERY_PSEUDO_PERMANENT | self::QUERY_CHANGE_SCHEMA
        );
        if ( !$ret ) {
            return $ret;
        }
 
        $res = $this->query(
            'SELECT attname FROM pg_class c'
            . ' JOIN pg_namespace n ON (n.oid = c.relnamespace)'
            . ' JOIN pg_attribute a ON (a.attrelid = c.oid)'
            . ' JOIN pg_attrdef d ON (c.oid=d.adrelid and a.attnum=d.adnum)'
            . ' WHERE relkind = \'r\''
            . ' AND nspname = ' . $this->addQuotes( $this->getCoreSchema() )
            . ' AND relname = ' . $this->addQuotes( $oldName )
            . ' AND pg_get_expr(adbin, adrelid) LIKE \'nextval(%\'',
            $fname,
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE
        );
        $row = $this->fetchObject( $res );
        if ( $row ) {
            $field = $row->attname;
            $newSeq = "{$newName}_{$field}_seq";
            $fieldE = $this->addIdentifierQuotes( $field );
            $newSeqE = $this->addIdentifierQuotes( $newSeq );
            $newSeqQ = $this->addQuotes( $newSeq );
            $this->query(
                "CREATE $temporary SEQUENCE $newSeqE OWNED BY $newNameE.$fieldE",
                $fname,
                self::QUERY_CHANGE_SCHEMA
            );
            $this->query(
                "ALTER TABLE $newNameE ALTER COLUMN $fieldE SET DEFAULT nextval({$newSeqQ}::regclass)",
                $fname,
                self::QUERY_CHANGE_SCHEMA
            );
        }
 
        return $ret;
    }
 
    protected function doTruncate( array $tables, $fname ) {
        $encTables = $this->tableNamesN( ...$tables );
        $sql = "TRUNCATE TABLE " . implode( ',', $encTables ) . " RESTART IDENTITY";
        $this->query( $sql, $fname, self::QUERY_CHANGE_SCHEMA );
    }
 
    public function listTables( $prefix = '', $fname = __METHOD__ ) {
        $eschemas = implode( ',', array_map( [ $this, 'addQuotes' ], $this->getCoreSchemas() ) );
        $result = $this->query(
            "SELECT DISTINCT tablename FROM pg_tables WHERE schemaname IN ($eschemas)",
            $fname,
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE
        );
        $endArray = [];
 
        foreach ( $result as $table ) {
            $vars = get_object_vars( $table );
            $table = array_pop( $vars );
            if ( $prefix == '' || strpos( $table, $prefix ) === 0 ) {
                $endArray[] = $table;
            }
        }
 
        return $endArray;
    }
 
    public function timestamp( $ts = 0 ) {
        $ct = new ConvertibleTimestamp( $ts );
 
        return $ct->getTimestamp( TS_POSTGRES );
    }
 
    private function pg_array_parse( $text, &$output, $limit = false, $offset = 1 ) {
        if ( $limit === false ) {
            $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]';
    }
 
    public function getCurrentSchema() {
        $res = $this->query(
            "SELECT current_schema()",
            __METHOD__,
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE
        );
        $row = $this->fetchRow( $res );
 
        return $row[0];
    }
 
    public function getSchemas() {
        $res = $this->query(
            "SELECT current_schemas(false)",
            __METHOD__,
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE
        );
        $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 );
    }
 
    public function getSearchPath() {
        $res = $this->query(
            "SHOW search_path",
            __METHOD__,
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE
        );
        $row = $this->fetchRow( $res );
 
        /* PostgreSQL returns SHOW values as strings */
 
        return explode( ",", $row[0] );
    }
 
    private function setSearchPath( $search_path ) {
        $this->query(
            "SET search_path = " . implode( ", ", $search_path ),
            __METHOD__,
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_TRX
        );
    }
 
    public function determineCoreSchema( $desiredSchema ) {
        if ( $this->trxLevel() ) {
            // We do not want the schema selection to change on ROLLBACK or INSERT SELECT.
            // See https://www.postgresql.org/docs/8.3/sql-set.html
            throw new DBUnexpectedError(
                $this,
                __METHOD__ . ": a transaction is currently active"
            );
        }
 
        if ( $this->schemaExists( $desiredSchema ) ) {
            if ( in_array( $desiredSchema, $this->getSchemas() ) ) {
                $this->coreSchema = $desiredSchema;
                $this->queryLogger->debug(
                    "Schema \"" . $desiredSchema . "\" already in the search path\n" );
            } else {
                // Prepend the desired schema to the search path (T17816)
                $search_path = $this->getSearchPath();
                array_unshift( $search_path, $this->addIdentifierQuotes( $desiredSchema ) );
                $this->setSearchPath( $search_path );
                $this->coreSchema = $desiredSchema;
                $this->queryLogger->debug(
                    "Schema \"" . $desiredSchema . "\" added to the search path\n" );
            }
        } else {
            $this->coreSchema = $this->getCurrentSchema();
            $this->queryLogger->debug(
                "Schema \"" . $desiredSchema . "\" not found, using current \"" .
                $this->coreSchema . "\"\n" );
        }
    }
 
    public function getCoreSchema() {
        return $this->coreSchema;
    }
 
    public function getCoreSchemas() {
        if ( $this->tempSchema ) {
            return [ $this->tempSchema, $this->getCoreSchema() ];
        }
 
        $res = $this->query(
            "SELECT nspname FROM pg_catalog.pg_namespace n WHERE n.oid = pg_my_temp_schema()",
            __METHOD__,
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE
        );
        $row = $this->fetchObject( $res );
        if ( $row ) {
            $this->tempSchema = $row->nspname;
            return [ $this->tempSchema, $this->getCoreSchema() ];
        }
 
        return [ $this->getCoreSchema() ];
    }
 
    public 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 {
                // T18937: broken pgsql extension from PHP<5.3
                $this->numericVersion = pg_parameter_status( $conn, 'server_version' );
            }
        }
 
        return $this->numericVersion;
    }
 
    private function relationExists( $table, $types, $schema = false ) {
        if ( !is_array( $types ) ) {
            $types = [ $types ];
        }
        if ( $schema === false ) {
            $schemas = $this->getCoreSchemas();
        } else {
            $schemas = [ $schema ];
        }
        $table = $this->realTableName( $table, 'raw' );
        $etable = $this->addQuotes( $table );
        foreach ( $schemas as $schema ) {
            $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,
                __METHOD__,
                self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE
            );
            if ( $res && $res->numRows() ) {
                return true;
            }
        }
 
        return false;
    }
 
    public function tableExists( $table, $fname = __METHOD__, $schema = false ) {
        return $this->relationExists( $table, [ 'r', 'v' ], $schema );
    }
 
    public function sequenceExists( $sequence, $schema = false ) {
        return $this->relationExists( $sequence, 'S', $schema );
    }
 
    public 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;
        foreach ( $this->getCoreSchemas() as $schema ) {
            $res = $this->query(
                sprintf(
                    $q,
                    $this->addQuotes( $schema ),
                    $this->addQuotes( $table ),
                    $this->addQuotes( $trigger )
                ),
                __METHOD__,
                self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE
            );
            if ( $res && $res->numRows() ) {
                return true;
            }
        }
 
        return false;
    }
 
    public function ruleExists( $table, $rule ) {
        $exists = $this->selectField( 'pg_rules', 'rulename',
            [
                'rulename' => $rule,
                'tablename' => $table,
                'schemaname' => $this->getCoreSchemas()
            ],
            __METHOD__
        );
 
        return $exists === $rule;
    }
 
    public function constraintExists( $table, $constraint ) {
        foreach ( $this->getCoreSchemas() as $schema ) {
            $sql = sprintf( "SELECT 1 FROM information_schema.table_constraints " .
                "WHERE constraint_schema = %s AND table_name = %s AND constraint_name = %s",
                $this->addQuotes( $schema ),
                $this->addQuotes( $table ),
                $this->addQuotes( $constraint )
            );
            $res = $this->query(
                $sql,
                __METHOD__,
                self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE
            );
            if ( $res && $res->numRows() ) {
                return true;
            }
        }
        return false;
    }
 
    public function schemaExists( $schema ) {
        if ( !strlen( $schema ) ) {
            return false; // short-circuit
        }
 
        $res = $this->query(
            "SELECT 1 FROM pg_catalog.pg_namespace " .
            "WHERE nspname = " . $this->addQuotes( $schema ) . " LIMIT 1",
            __METHOD__,
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE
        );
 
        return ( $this->numRows( $res ) > 0 );
    }
 
    public function roleExists( $roleName ) {
        $res = $this->query(
            "SELECT 1 FROM pg_catalog.pg_roles " .
            "WHERE rolname = " . $this->addQuotes( $roleName ) . " LIMIT 1",
            __METHOD__,
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE
        );
 
        return ( $this->numRows( $res ) > 0 );
    }
 
    public function fieldInfo( $table, $field ) {
        return PostgresField::fromText( $this, $table, $field );
    }
 
    public function fieldType( $res, $index ) {
        wfDeprecated( __METHOD__, '1.37' );
        return pg_field_type( $res->getInternalResult(), $index );
    }
 
    public function encodeBlob( $b ) {
        return new PostgresBlob( pg_escape_bytea( $b ) );
    }
 
    public function decodeBlob( $b ) {
        if ( $b instanceof PostgresBlob ) {
            $b = $b->fetch();
        } elseif ( $b instanceof Blob ) {
            return $b->fetch();
        }
 
        return pg_unescape_bytea( $b );
    }
 
    public function strencode( $s ) {
        // Should not be called by us
        return pg_escape_string( $this->getBindingHandle(), (string)$s );
    }
 
    public function addQuotes( $s ) {
        $conn = $this->getBindingHandle();
 
        if ( $s === null ) {
            return 'NULL';
        } elseif ( is_bool( $s ) ) {
            return (string)intval( $s );
        } elseif ( is_int( $s ) ) {
            return (string)$s;
        } elseif ( $s instanceof Blob ) {
            if ( $s instanceof PostgresBlob ) {
                $s = $s->fetch();
            } else {
                $s = pg_escape_bytea( $conn, $s->fetch() );
            }
            return "'$s'";
        } elseif ( $s instanceof NextSequenceValue ) {
            return 'DEFAULT';
        }
 
        return "'" . pg_escape_string( $conn, (string)$s ) . "'";
    }
 
    protected function makeSelectOptions( array $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['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 ];
    }
 
    public function buildConcat( $stringList ) {
        return implode( ' || ', $stringList );
    }
 
    public function buildGroupConcatField(
        $delim, $table, $field, $conds = '', $join_conds = []
    ) {
        $fld = "array_to_string(array_agg($field)," . $this->addQuotes( $delim ) . ')';
 
        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 doLockTables( array $read, array $write, $method ) {
        $tablesWrite = [];
        foreach ( $write as $table ) {
            $tablesWrite[] = $this->tableName( $table );
        }
        $tablesRead = [];
        foreach ( $read as $table ) {
            $tablesRead[] = $this->tableName( $table );
        }
 
        // Acquire locks for the duration of the current transaction...
        if ( $tablesWrite ) {
            $this->query(
                'LOCK TABLE ONLY ' . implode( ',', $tablesWrite ) . ' IN EXCLUSIVE MODE',
                $method,
                self::QUERY_CHANGE_ROWS
            );
        }
        if ( $tablesRead ) {
            $this->query(
                'LOCK TABLE ONLY ' . implode( ',', $tablesRead ) . ' IN SHARE MODE',
                $method,
                self::QUERY_CHANGE_ROWS
            );
        }
 
        return true;
    }
 
    public function doLockIsFree( string $lockName, string $method ) {
        // http://www.postgresql.org/docs/9.2/static/functions-admin.html#FUNCTIONS-ADVISORY-LOCKS
        $key = $this->addQuotes( $this->bigintFromLockName( $lockName ) );
 
        $res = $this->query(
            "SELECT (CASE(pg_try_advisory_lock($key))
            WHEN 'f' THEN 'f' ELSE pg_advisory_unlock($key) END) AS unlocked",
            $method,
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE
        );
        $row = $this->fetchObject( $res );
 
        return ( $row->unlocked === 't' );
    }
 
    public function doLock( string $lockName, string $method, int $timeout ) {
        // http://www.postgresql.org/docs/9.2/static/functions-admin.html#FUNCTIONS-ADVISORY-LOCKS
        $key = $this->addQuotes( $this->bigintFromLockName( $lockName ) );
 
        $acquired = null;
        $loop = new WaitConditionLoop(
            function () use ( $lockName, $key, $timeout, $method, &$acquired ) {
                $res = $this->query(
                    "SELECT (CASE WHEN pg_try_advisory_lock($key) " .
                        "THEN EXTRACT(epoch from clock_timestamp()) " .
                        "ELSE NULL " .
                    "END) AS acquired",
                    $method,
                    self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_ROWS
                );
                $row = $this->fetchObject( $res );
 
                if ( $row->acquired !== null ) {
                    $acquired = (float)$row->acquired;
 
                    return WaitConditionLoop::CONDITION_REACHED;
                }
 
                return WaitConditionLoop::CONDITION_CONTINUE;
            },
            $timeout
        );
        $loop->invoke();
 
        return $acquired;
    }
 
    public function doUnlock( string $lockName, string $method ) {
        // http://www.postgresql.org/docs/9.2/static/functions-admin.html#FUNCTIONS-ADVISORY-LOCKS
        $key = $this->addQuotes( $this->bigintFromLockName( $lockName ) );
 
        $result = $this->query(
            "SELECT pg_advisory_unlock($key) AS released",
            $method,
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_ROWS
        );
        $row = $this->fetchObject( $result );
 
        return ( $row->released === 't' );
    }
 
    public function serverIsReadOnly() {
        $res = $this->query(
            "SHOW default_transaction_read_only",
            __METHOD__,
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE
        );
        $row = $this->fetchObject( $res );
 
        return $row ? ( strtolower( $row->default_transaction_read_only ) === 'on' ) : false;
    }
 
    protected static function getAttributes() {
        return [ self::ATTR_SCHEMAS_AS_TABLE_GROUPS => true ];
    }
 
    private function bigintFromLockName( $lockName ) {
        return \Wikimedia\base_convert( substr( sha1( $lockName ), 0, 15 ), 16, 10 );
    }
}
 
class_alias( DatabasePostgres::class, 'DatabasePostgres' );