DatabasePostgres.php

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<?php
// Suppress UnusedPluginSuppression because Phan on PHP 7.4 and PHP 8.1 need different suppressions
// @phan-file-suppress UnusedPluginSuppression,UnusedPluginFileSuppression
 
namespace Wikimedia\Rdbms;
 
use RuntimeException;
use Wikimedia\Rdbms\Platform\PostgresPlatform;
use Wikimedia\Rdbms\Replication\ReplicationReporter;
use Wikimedia\WaitConditionLoop;
 
class DatabasePostgres extends Database {
    private $port;
    private $tempSchema;
    private $numericVersion;
 
    private $lastResultHandle;
 
    protected $platform;
 
    public function __construct( array $params ) {
        $this->port = intval( $params['port'] ?? null );
        parent::__construct( $params );
 
        $this->platform = new PostgresPlatform(
            $this,
            $this->logger,
            $this->currentDomain,
            $this->errorLogger
        );
        $this->replicationReporter = new ReplicationReporter(
            $params['topologyRole'],
            $this->logger,
            $params['srvCache']
        );
    }
 
    public function getType() {
        return 'postgres';
    }
 
    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' => ( $db !== null && $db !== '' ) ? $db : 'postgres',
            'user' => $user,
            'password' => $password
        ];
        if ( $server !== null && $server !== '' ) {
            $connectVars['host'] = $server;
        }
        if ( $this->port > 0 ) {
            $connectVars['port'] = $this->port;
        }
        if ( $this->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 ) {
                $sql = 'SET ' . $this->platform->addIdentifierQuotes( $var ) . ' = ' . $this->addQuotes( $val );
                $query = new Query( $sql, self::QUERY_NO_RETRY | self::QUERY_CHANGE_TRX, 'SET' );
                $this->query( $query, __METHOD__ );
            }
            $this->determineCoreSchema( $schema );
            $this->currentDomain = new DatabaseDomain( $db, $schema, $tablePrefix );
            $this->platform->setCurrentDomain( $this->currentDomain );
        } catch ( RuntimeException $e ) {
            throw $this->newExceptionAfterConnectError( $e->getMessage() );
        }
    }
 
    public function databasesAreIndependent() {
        return true;
    }
 
    public function doSelectDomain( DatabaseDomain $domain ) {
        $database = $domain->getDatabase();
        if ( $database === null ) {
            // A null database means "don't care" so leave it as is and update the table prefix
            $this->currentDomain = new DatabaseDomain(
                $this->currentDomain->getDatabase(),
                $domain->getSchema() ?? $this->currentDomain->getSchema(),
                $domain->getTablePrefix()
            );
            $this->platform->setCurrentDomain( $this->currentDomain );
        } elseif ( $this->getDBname() !== $database ) {
            // 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],
                $database,
                $domain->getSchema(),
                $domain->getTablePrefix()
            );
        } else {
            $this->currentDomain = $domain;
            $this->platform->setCurrentDomain( $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;
    }
 
    public function doSingleStatementQuery( string $sql ): QueryStatus {
        $conn = $this->getBindingHandle();
 
        $sql = mb_convert_encoding( $sql, 'UTF-8' );
        // Clear any previously left over result
        // phpcs:ignore Generic.CodeAnalysis.AssignmentInCondition.FoundInWhileCondition
        while ( $priorRes = pg_get_result( $conn ) ) {
            pg_free_result( $priorRes );
        }
 
        if ( pg_send_query( $conn, $sql ) === false ) {
            throw new DBUnexpectedError( $this, "Unable to post new query to PostgreSQL\n" );
        }
 
        // Newer PHP versions use PgSql\Result instead of resource variables
        // https://www.php.net/manual/en/function.pg-get-result.php
        $pgRes = pg_get_result( $conn );
        // Phan on PHP 7.4 and PHP 8.1 need different suppressions
        // @phan-suppress-next-line PhanTypeMismatchProperty,PhanTypeMismatchPropertyProbablyReal
        $this->lastResultHandle = $pgRes;
        $res = pg_result_error( $pgRes ) ? false : $pgRes;
 
        return new QueryStatus(
            // @phan-suppress-next-line PhanTypeMismatchArgument
            is_bool( $res ) ? $res : new PostgresResultWrapper( $this, $conn, $res ),
            $pgRes ? pg_affected_rows( $pgRes ) : 0,
            $this->lastError(),
            $this->lastErrno()
        );
    }
 
    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->logger->debug( sprintf( "PgSQL ERROR(%d): %s",
                // @phan-suppress-next-line PhanTypeMismatchArgumentInternal
                $d, pg_result_error_field( $this->lastResultHandle, $d ) ) );
        }
    }
 
    protected function lastInsertId() {
        // Avoid using query() to prevent unwanted side-effects like changing affected
        // row counts or connection retries. Note that lastval() is connection-specific.
        // Note that this causes "lastval is not yet defined in this session" errors if
        // nextval() was never directly or implicitly triggered (error out any transaction).
        $qs = $this->doSingleStatementQuery( "SELECT lastval() AS id" );
 
        return $qs->res ? (int)$qs->res->fetchRow()['id'] : 0;
    }
 
    public function lastError() {
        if ( $this->conn ) {
            if ( $this->lastResultHandle ) {
                // @phan-suppress-next-line PhanTypeMismatchArgumentInternal
                return pg_result_error( $this->lastResultHandle );
            } else {
                return pg_last_error() ?: $this->lastConnectError;
            }
        }
 
        return $this->getLastPHPError() ?: 'No database connection';
    }
 
    public function lastErrno() {
        if ( $this->lastResultHandle ) {
            // @phan-suppress-next-line PhanTypeMismatchArgumentInternal
            $lastErrno = pg_result_error_field( $this->lastResultHandle, PGSQL_DIAG_SQLSTATE );
            if ( $lastErrno !== false ) {
                return $lastErrno;
            }
        }
 
        return '00000';
    }
 
    public function estimateRowCount( $table, $var = '*', $conds = '',
        $fname = __METHOD__, $options = [], $join_conds = []
    ): int {
        $conds = $this->platform->normalizeConditions( $conds, $fname );
        $column = $this->platform->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 = $res->fetchRow();
            $count = [];
            if ( preg_match( '/rows=(\d+)/', $row[0], $count ) ) {
                $rows = (int)$count[1];
            }
        }
 
        return $rows;
    }
 
    public function indexInfo( $table, $index, $fname = __METHOD__ ) {
        $components = $this->platform->qualifiedTableComponents( $table );
        if ( count( $components ) === 1 ) {
            $schema = $this->getCoreSchema();
            $tableComponent = $components[0];
        } elseif ( count( $components ) === 2 ) {
            [ $schema, $tableComponent ] = $components;
        } else {
            [ , $schema, $tableComponent ] = $components;
        }
        $encSchema = $this->addQuotes( $schema );
        $encTable = $this->addQuotes( $tableComponent );
        $encIndex = $this->addQuotes( $this->platform->indexName( $index ) );
        $query = new Query(
            "SELECT indexname,indexdef FROM pg_indexes " .
                "WHERE schemaname=$encSchema AND tablename=$encTable AND indexname=$encIndex",
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE,
            'SELECT'
        );
        $res = $this->query( $query );
        $row = $res->fetchObject();
 
        if ( $row ) {
            return [ 'unique' => ( strpos( $row->indexdef, 'CREATE UNIQUE ' ) === 0 ) ];
        }
 
        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__;
            $query = new Query( $sql, $flags, 'SELECT' );
            $res = $this->query( $query, __METHOD__ );
            $a = [];
            if ( $res ) {
                foreach ( $res as $row ) {
                    $a[] = [
                        $row->attname,
                        $row->opcname,
                        $row->amname,
                        $row->option ];
                }
                return $a;
            }
        }
        return null;
    }
 
    protected function doInsertSelectNative(
        $destTable,
        $srcTable,
        array $varMap,
        $conds,
        $fname,
        array $insertOptions,
        array $selectOptions,
        $selectJoinConds
    ) {
        if ( in_array( 'IGNORE', $insertOptions ) ) {
            // Use "ON CONFLICT DO" if we have it for IGNORE
            $destTableEnc = $this->tableName( $destTable );
 
            $selectSql = $this->selectSQLText(
                $srcTable,
                array_values( $varMap ),
                $conds,
                $fname,
                $selectOptions,
                $selectJoinConds
            );
 
            $sql = "INSERT INTO $destTableEnc (" . implode( ',', array_keys( $varMap ) ) . ') ' .
                $selectSql . ' ON CONFLICT DO NOTHING';
            $query = new Query( $sql, self::QUERY_CHANGE_ROWS, 'INSERT', $destTable );
            $this->query( $query, $fname );
        } else {
            parent::doInsertSelectNative( $destTable, $srcTable, $varMap, $conds, $fname,
                $insertOptions, $selectOptions, $selectJoinConds );
        }
    }
 
    public function getValueTypesForWithClause( $table ) {
        $typesByColumn = [];
 
        $flags = self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE;
        $encTable = $this->addQuotes( $table );
        foreach ( $this->getCoreSchemas() as $schema ) {
            $encSchema = $this->addQuotes( $schema );
            $sql = "SELECT column_name,udt_name " .
                "FROM information_schema.columns " .
                "WHERE table_name = $encTable AND table_schema = $encSchema";
            $query = new Query( $sql, $flags, 'SELECT' );
            $res = $this->query( $query, __METHOD__ );
            if ( $res->numRows() ) {
                foreach ( $res as $row ) {
                    $typesByColumn[$row->column_name] = $row->udt_name;
                }
                break;
            }
        }
 
        return $typesByColumn;
    }
 
    protected function isConnectionError( $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 isQueryTimeoutError( $errno ) {
        // https://www.postgresql.org/docs/9.2/static/errcodes-appendix.html
        return ( $errno === '57014' );
    }
 
    protected function isKnownStatementRollbackError( $errno ) {
        return false; // transaction has to be rolled-back from error state
    }
 
    public function duplicateTableStructure(
        $oldName, $newName, $temporary = false, $fname = __METHOD__
    ) {
        $newNameE = $this->platform->addIdentifierQuotes( $newName );
        $oldNameE = $this->platform->addIdentifierQuotes( $oldName );
 
        $temporary = $temporary ? 'TEMPORARY' : '';
        $query = new Query(
            "CREATE $temporary TABLE $newNameE " .
            "(LIKE $oldNameE INCLUDING DEFAULTS INCLUDING INDEXES)",
            self::QUERY_PSEUDO_PERMANENT | self::QUERY_CHANGE_SCHEMA,
            $temporary ? 'CREATE TEMPORARY' : 'CREATE',
            // Use a dot to avoid double-prefixing in Database::getTempTableWrites()
            '.' . $newName
        );
        $ret = $this->query( $query, $fname );
        if ( !$ret ) {
            return $ret;
        }
 
        $sql = '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(%\'';
        $query = new Query(
            $sql,
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE,
            'SELECT'
        );
 
        $res = $this->query( $query, $fname );
        $row = $res->fetchObject();
        if ( $row ) {
            $field = $row->attname;
            $newSeq = "{$newName}_{$field}_seq";
            $fieldE = $this->platform->addIdentifierQuotes( $field );
            $newSeqE = $this->platform->addIdentifierQuotes( $newSeq );
            $newSeqQ = $this->addQuotes( $newSeq );
            $query = new Query(
                "CREATE $temporary SEQUENCE $newSeqE OWNED BY $newNameE.$fieldE",
                self::QUERY_CHANGE_SCHEMA,
                'CREATE',
                // Do not treat this is as a table modification on top of the CREATE above.
                null
            );
            $this->query( $query, $fname );
            $query = new Query(
                "ALTER TABLE $newNameE ALTER COLUMN $fieldE SET DEFAULT nextval({$newSeqQ}::regclass)",
                self::QUERY_CHANGE_SCHEMA,
                'ALTER',
                // Do not treat this is as a table modification on top of the CREATE above.
                null
            );
            $this->query( $query, $fname );
        }
 
        return $ret;
    }
 
    public function truncateTable( $table, $fname = __METHOD__ ) {
        $sql = "TRUNCATE TABLE " . $this->tableName( $table ) . " RESTART IDENTITY";
        $query = new Query( $sql, self::QUERY_CHANGE_SCHEMA, 'TRUNCATE', $table );
        $this->query( $query, $fname );
    }
 
    public function listTables( $prefix = '', $fname = __METHOD__ ) {
        $eschemas = implode( ',', array_map( [ $this, 'addQuotes' ], $this->getCoreSchemas() ) );
        $query = new Query(
            "SELECT DISTINCT tablename FROM pg_tables WHERE schemaname IN ($eschemas)",
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE,
            'SELECT'
        );
        $result = $this->query( $query, $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;
    }
 
    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 getSoftwareLink() {
        return '[{{int:version-db-postgres-url}} PostgreSQL]';
    }
 
    public function getCurrentSchema() {
        $query = new Query(
            "SELECT current_schema()",
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE,
            'SELECT'
        );
        $res = $this->query( $query, __METHOD__ );
        $row = $res->fetchRow();
 
        return $row[0];
    }
 
    public function getSchemas() {
        $query = new Query(
            "SELECT current_schemas(false)",
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE,
            'SELECT'
        );
        $res = $this->query( $query, __METHOD__ );
        $row = $res->fetchRow();
        $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() {
        $query = new Query(
            "SHOW search_path",
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE,
            'SHOW'
        );
        $res = $this->query( $query, __METHOD__ );
        $row = $res->fetchRow();
 
        /* PostgreSQL returns SHOW values as strings */
 
        return explode( ",", $row[0] );
    }
 
    private function setSearchPath( $search_path ) {
        $query = new Query(
            "SET search_path = " . implode( ", ", $search_path ),
            self::QUERY_CHANGE_TRX,
            'SET'
        );
        $this->query( $query, __METHOD__ );
    }
 
    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->platform->setCoreSchema( $desiredSchema );
                $this->logger->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->platform->addIdentifierQuotes( $desiredSchema ) );
                $this->setSearchPath( $search_path );
                $this->platform->setCoreSchema( $desiredSchema );
                $this->logger->debug(
                    "Schema \"" . $desiredSchema . "\" added to the search path\n" );
            }
        } else {
            $this->platform->setCoreSchema( $this->getCurrentSchema() );
            $this->logger->debug(
                "Schema \"" . $desiredSchema . "\" not found, using current \"" .
                $this->getCoreSchema() . "\"\n" );
        }
    }
 
    public function getCoreSchema() {
        return $this->platform->getCoreSchema();
    }
 
    public function getCoreSchemas() {
        if ( $this->tempSchema ) {
            return [ $this->tempSchema, $this->getCoreSchema() ];
        }
        $query = new Query(
            "SELECT nspname FROM pg_catalog.pg_namespace n WHERE n.oid = pg_my_temp_schema()",
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE,
            'SELECT'
        );
        $res = $this->query( $query, __METHOD__ );
        $row = $res->fetchObject();
        if ( $row ) {
            $this->tempSchema = $row->nspname;
            return [ $this->tempSchema, $this->getCoreSchema() ];
        }
 
        return [ $this->getCoreSchema() ];
    }
 
    public function getServerVersion() {
        if ( !isset( $this->numericVersion ) ) {
            // Works on PG 7.4+
            $this->numericVersion = pg_version( $this->getBindingHandle() )['server'];
        }
 
        return $this->numericVersion;
    }
 
    private function relationExists( $table, $types ) {
        if ( !is_array( $types ) ) {
            $types = [ $types ];
        }
        $schemas = $this->getCoreSchemas();
        $components = $this->platform->qualifiedTableComponents( $table );
        $etable = $this->addQuotes( end( $components ) );
        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 ) . "')";
            $query = new Query(
                $sql,
                self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE,
                'SELECT'
            );
            $res = $this->query( $query, __METHOD__ );
            if ( $res && $res->numRows() ) {
                return true;
            }
        }
 
        return false;
    }
 
    public function tableExists( $table, $fname = __METHOD__ ) {
        return $this->relationExists( $table, [ 'r', 'v' ] );
    }
 
    public function sequenceExists( $sequence ) {
        return $this->relationExists( $sequence, 'S' );
    }
 
    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 )
            );
            $query = new Query(
                $sql,
                self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE,
                'SELECT'
            );
            $res = $this->query( $query, __METHOD__ );
            if ( $res && $res->numRows() ) {
                return true;
            }
        }
        return false;
    }
 
    public function schemaExists( $schema ) {
        if ( !strlen( $schema ?? '' ) ) {
            return false; // short-circuit
        }
        $query = new Query(
            "SELECT 1 FROM pg_catalog.pg_namespace " .
            "WHERE nspname = " . $this->addQuotes( $schema ) . " LIMIT 1",
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE,
            'SELECT'
        );
        $res = $this->query( $query, __METHOD__ );
 
        return ( $res->numRows() > 0 );
    }
 
    public function roleExists( $roleName ) {
        $query = new Query(
            "SELECT 1 FROM pg_catalog.pg_roles " .
            "WHERE rolname = " . $this->addQuotes( $roleName ) . " LIMIT 1",
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE,
            'SELECT'
        );
        $res = $this->query( $query, __METHOD__ );
 
        return ( $res->numRows() > 0 );
    }
 
    public function fieldInfo( $table, $field ) {
        return PostgresField::fromText( $this, $table, $field );
    }
 
    public function encodeBlob( $b ) {
        $conn = $this->getBindingHandle();
 
        return new PostgresBlob( pg_escape_bytea( $conn, $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 ) {
        if ( $s instanceof RawSQLValue ) {
            return $s->toSql();
        }
        $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'";
        }
 
        return "'" . pg_escape_string( $conn, (string)$s ) . "'";
    }
 
    public function streamStatementEnd( &$sql, &$newLine ) {
        # Allow dollar quoting for function declarations
        if ( str_starts_with( $newLine, '$mw$' ) ) {
            if ( $this->delimiter ) {
                $this->delimiter = false;
            } else {
                $this->delimiter = ';';
            }
        }
 
        return parent::streamStatementEnd( $sql, $newLine );
    }
 
    public function doLockIsFree( string $lockName, string $method ) {
        $query = new Query(
            $this->platform->lockIsFreeSQLText( $lockName ),
            self::QUERY_CHANGE_LOCKS,
            'SELECT'
        );
        $res = $this->query( $query, $method );
        $row = $res->fetchObject();
 
        return (bool)$row->unlocked;
    }
 
    public function doLock( string $lockName, string $method, int $timeout ) {
        $query = new Query(
            $this->platform->lockSQLText( $lockName, $timeout ),
            self::QUERY_CHANGE_LOCKS,
            'SELECT'
        );
 
        $acquired = null;
        $loop = new WaitConditionLoop(
            function () use ( $query, $method, &$acquired ) {
                $res = $this->query( $query, $method );
                $row = $res->fetchObject();
 
                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 ) {
        $query = new Query(
            $this->platform->unlockSQLText( $lockName ),
            self::QUERY_CHANGE_LOCKS,
            'SELECT'
        );
        $result = $this->query( $query, $method );
        $row = $result->fetchObject();
 
        return (bool)$row->released;
    }
 
    protected function doFlushSession( $fname ) {
        $flags = self::QUERY_CHANGE_LOCKS | self::QUERY_NO_RETRY;
 
        // https://www.postgresql.org/docs/9.1/functions-admin.html
        $sql = "SELECT pg_advisory_unlock_all()";
        $query = new Query( $sql, $flags, 'UNLOCK' );
        $qs = $this->executeQuery( $query, __METHOD__, $flags );
        if ( $qs->res === false ) {
            $this->reportQueryError( $qs->message, $qs->code, $sql, $fname, true );
        }
    }
 
    public function serverIsReadOnly() {
        $query = new Query(
            "SHOW default_transaction_read_only",
            self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE,
            'SHOW'
        );
        $res = $this->query( $query, __METHOD__ );
        $row = $res->fetchObject();
 
        return $row && strtolower( $row->default_transaction_read_only ) === 'on';
    }
 
    protected function getInsertIdColumnForUpsert( $table ) {
        $column = null;
 
        $flags = self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE;
        $components = $this->platform->qualifiedTableComponents( $table );
        $encTable = $this->addQuotes( end( $components ) );
        foreach ( $this->getCoreSchemas() as $schema ) {
            $encSchema = $this->addQuotes( $schema );
            $query = new Query(
                "SELECT column_name,data_type,column_default " .
                    "FROM information_schema.columns " .
                    "WHERE table_name = $encTable AND table_schema = $encSchema",
                self::QUERY_IGNORE_DBO_TRX | self::QUERY_CHANGE_NONE,
                'SELECT'
            );
            $res = $this->query( $query, __METHOD__ );
            if ( $res->numRows() ) {
                foreach ( $res as $row ) {
                    if (
                        $row->column_default !== null &&
                        str_starts_with( $row->column_default, "nextval(" ) &&
                        in_array( $row->data_type, [ 'integer', 'bigint' ], true )
                    ) {
                        $column = $row->column_name;
                    }
                }
                break;
            }
        }
 
        return $column;
    }
 
    public static function getAttributes() {
        return [ self::ATTR_SCHEMAS_AS_TABLE_GROUPS => true ];
    }
}