Proyectos de Subversion Moodle

<?php

// This file is part of Moodle - http://moodle.org/

//

// Moodle is free software: you can redistribute it and/or modify

// it under the terms of the GNU General Public License as published by

// the Free Software Foundation, either version 3 of the License, or

// (at your option) any later version.

//

// Moodle is distributed in the hope that it will be useful,

// but WITHOUT ANY WARRANTY; without even the implied warranty of

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

// GNU General Public License for more details.

//

// You should have received a copy of the GNU General Public License

// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.

/**

 * Native pgsql class representing moodle database interface.

 *

 * @package    core_dml

 * @copyright  2008 Petr Skoda (http://skodak.org)

 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later

 */

defined('MOODLE_INTERNAL') || die();

require_once(__DIR__.'/moodle_database.php');

require_once(__DIR__.'/moodle_read_slave_trait.php');

require_once(__DIR__.'/pgsql_native_moodle_recordset.php');

require_once(__DIR__.'/pgsql_native_moodle_temptables.php');

/**

 * Native pgsql class representing moodle database interface.

 *

 * @package    core_dml

 * @copyright  2008 Petr Skoda (http://skodak.org)

 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later

 */

class pgsql_native_moodle_database extends moodle_database {

    use moodle_read_slave_trait {

        select_db_handle as read_slave_select_db_handle;

        can_use_readonly as read_slave_can_use_readonly;

        query_start as read_slave_query_start;

        query_end as read_slave_query_end;

    }

    /** @var array $sslmodes */

    private static $sslmodes = [

        'disable',

        'prefer',

        'require',

        'verify-full'

    ];

    /** @var array $serverinfo cache */

    private $serverinfo = [];

    /** @var array $dbhcursor keep track of open cursors */

    private $dbhcursor = [];

    /** @var resource|PgSql\Connection|null $pgsql database resource */

    protected $pgsql     = null;

    protected $last_error_reporting; // To handle pgsql driver default verbosity

    /** @var bool savepoint hack for MDL-35506 - workaround for automatic transaction rollback on error */

    protected $savepointpresent = false;

    /** @var int Number of cursors used (for constructing a unique ID) */

    protected $cursorcount = 0;

    /** @var int Default number of rows to fetch at a time when using recordsets with cursors */

    const DEFAULT_FETCH_BUFFER_SIZE = 100000;

    /**

     * Detects if all needed PHP stuff installed.

     * Note: can be used before connect()

     * @return mixed true if ok, string if something

     */

    public function driver_installed() {

        if (!extension_loaded('pgsql')) {

            return get_string('pgsqlextensionisnotpresentinphp', 'install');

        }

        return true;

    }

    /**

     * Returns database family type - describes SQL dialect

     * Note: can be used before connect()

     * @return string db family name (mysql, postgres, mssql, oracle, etc.)

     */

    public function get_dbfamily() {

        return 'postgres';

    }

    /**

     * Returns more specific database driver type

     * Note: can be used before connect()

     * @return string db type mysqli, pgsql, oci, mssql, sqlsrv

     */

    protected function get_dbtype() {

        return 'pgsql';

    }

    /**

     * Returns general database library name

     * Note: can be used before connect()

     * @return string db type pdo, native

     */

    protected function get_dblibrary() {

        return 'native';

    }

    /**

     * Returns localised database type name

     * Note: can be used before connect()

     * @return string

     */

    public function get_name() {

        return get_string('nativepgsql', 'install');

    }

    /**

     * Returns localised database configuration help.

     * Note: can be used before connect()

     * @return string

     */

    public function get_configuration_help() {

        return get_string('nativepgsqlhelp', 'install');

    }

    /**

     * Connect to db

     * @param string $dbhost The database host.

     * @param string $dbuser The database username.

     * @param string $dbpass The database username's password.

     * @param string $dbname The name of the database being connected to.

     * @param mixed $prefix string means moodle db prefix, false used for external databases where prefix not used

     * @param array $dboptions driver specific options

     * @return bool true

     * @throws moodle_exception

     * @throws dml_connection_exception if error

     */

    public function raw_connect(string $dbhost, string $dbuser, string $dbpass, string $dbname, $prefix, array $dboptions=null): bool {

        if ($prefix == '' and !$this->external) {

            //Enforce prefixes for everybody but mysql

            throw new dml_exception('prefixcannotbeempty', $this->get_dbfamily());

        }

        $driverstatus = $this->driver_installed();

        if ($driverstatus !== true) {

            throw new dml_exception('dbdriverproblem', $driverstatus);

        }

        $this->store_settings($dbhost, $dbuser, $dbpass, $dbname, $prefix, $dboptions);

        $pass = addcslashes($this->dbpass, "'\\");

        // Unix socket connections should have lower overhead

        if (!empty($this->dboptions['dbsocket']) and ($this->dbhost === 'localhost' or $this->dbhost === '127.0.0.1')) {

            $connection = "user='$this->dbuser' password='$pass' dbname='$this->dbname'";

            if (strpos($this->dboptions['dbsocket'], '/') !== false) {

                // A directory was specified as the socket location.

                $connection .= " host='".$this->dboptions['dbsocket']."'";

            }

            if (!empty($this->dboptions['dbport'])) {

                // A port as specified, add it to the connection as it's used as part of the socket path.

                $connection .= " port ='".$this->dboptions['dbport']."'";

            }

        } else {

            $this->dboptions['dbsocket'] = '';

            if (empty($this->dbname)) {

                // probably old style socket connection - do not add port

                $port = "";

            } else if (empty($this->dboptions['dbport'])) {

                $port = "port ='5432'";

            } else {

                $port = "port ='".$this->dboptions['dbport']."'";

            }

            $connection = "host='$this->dbhost' $port user='$this->dbuser' password='$pass' dbname='$this->dbname'";

        }

        if (!empty($this->dboptions['connecttimeout'])) {

            $connection .= " connect_timeout=".$this->dboptions['connecttimeout'];

        }

        if (empty($this->dboptions['dbhandlesoptions'])) {

            // ALTER USER and ALTER DATABASE are overridden by these settings.

            $options = array('--client_encoding=utf8', '--standard_conforming_strings=on');

            // Select schema if specified, otherwise the first one wins.

            if (!empty($this->dboptions['dbschema'])) {

                $options[] = "-c search_path=" . addcslashes($this->dboptions['dbschema'], "'\\");

            }

            $connection .= " options='" . implode(' ', $options) . "'";

        }

        if (isset($this->dboptions['ssl'])) {

            $sslmode = $this->dboptions['ssl'];

            if (!in_array($sslmode, self::$sslmodes, true)) {

                throw new moodle_exception('validateerrorlist', 'admin', '', "'dboptions''ssl': $sslmode");

            }

            $connection .= " sslmode=$sslmode";

        }

        ob_start();

        // It seems that pg_connect() handles some errors differently.

        // For example, name resolution error will raise an exception, and non-existing

        // database or wrong credentials will just return false.

        // We need to cater for both.

        try {

            if (empty($this->dboptions['dbpersist'])) {

                $this->pgsql = pg_connect($connection, PGSQL_CONNECT_FORCE_NEW);

            } else {

                $this->pgsql = pg_pconnect($connection, PGSQL_CONNECT_FORCE_NEW);

            }

            $dberr = ob_get_contents();

        } catch (\Exception $e) {

            $dberr = $e->getMessage();

        }

        ob_end_clean();

        $status = $this->pgsql ? pg_connection_status($this->pgsql) : false;

        if ($status === false or $status === PGSQL_CONNECTION_BAD) {

            $this->pgsql = null;

            throw new dml_connection_exception($dberr);

        }

        if (!empty($this->dboptions['dbpersist'])) {

            // There are rare situations (such as PHP out of memory errors) when open cursors may

            // not be closed at the end of a connection. When using persistent connections, the

            // cursors remain open and 'get in the way' of future connections. To avoid this

            // problem, close all cursors here.

            $result = pg_query($this->pgsql, 'CLOSE ALL');

            if ($result) {

                pg_free_result($result);

            }

        }

        if (!empty($this->dboptions['dbhandlesoptions'])) {

            /* We don't trust people who just set the dbhandlesoptions, this code checks up on them.

             * These functions do not talk to the server, they use the client library knowledge to determine state.

             */

            if (!empty($this->dboptions['dbschema'])) {

                throw new dml_connection_exception('You cannot specify a schema with dbhandlesoptions, use the database to set it.');

            }

            if (pg_client_encoding($this->pgsql) != 'UTF8') {

                throw new dml_connection_exception('client_encoding = UTF8 not set, it is: ' . pg_client_encoding($this->pgsql));

            }

            if (pg_escape_string($this->pgsql, '\\') != '\\') {

                throw new dml_connection_exception('standard_conforming_strings = on, must be set at the database.');

            }

        }

        // Connection stabilised and configured, going to instantiate the temptables controller

        $this->temptables = new pgsql_native_moodle_temptables($this);

        return true;

    }

    /**

     * Close database connection and release all resources

     * and memory (especially circular memory references).

     * Do NOT use connect() again, create a new instance if needed.

     */

    public function dispose() {

        parent::dispose(); // Call parent dispose to write/close session and other common stuff before closing connection

        if ($this->pgsql) {

            pg_close($this->pgsql);

            $this->pgsql = null;

        }

    }

    /**

     * Gets db handle currently used with queries

     * @return resource

     */

    protected function get_db_handle() {

        return $this->pgsql;

    }

    /**

     * Sets db handle to be used with subsequent queries

     * @param resource $dbh

     * @return void

     */

    protected function set_db_handle($dbh): void {

        $this->pgsql = $dbh;

    }

    /**

     * Select appropriate db handle - readwrite or readonly

     * @param int $type type of query

     * @param string $sql

     * @return void

     */

    protected function select_db_handle(int $type, string $sql): void {

        $this->read_slave_select_db_handle($type, $sql);

        if (preg_match('/^DECLARE (crs\w*) NO SCROLL CURSOR/', $sql, $match)) {

            $cursor = $match[1];

            $this->dbhcursor[$cursor] = $this->pgsql;

        }

        if (preg_match('/^(?:FETCH \d+ FROM|CLOSE) (crs\w*)\b/', $sql, $match)) {

            $cursor = $match[1];

            $this->pgsql = $this->dbhcursor[$cursor];

        }

    }

    /**

     * Check if The query qualifies for readonly connection execution

     * Logging queries are exempt, those are write operations that circumvent

     * standard query_start/query_end paths.

     * @param int $type type of query

     * @param string $sql

     * @return bool

     */

    protected function can_use_readonly(int $type, string $sql): bool {

        // ... pg_*lock queries always go to master.

        if (preg_match('/\bpg_\w*lock/', $sql)) {

            return false;

        }

        // ... a nuisance - temptables use this.

        if (preg_match('/\bpg_catalog/', $sql) && $this->temptables->get_temptables()) {

            return false;

        }

        return $this->read_slave_can_use_readonly($type, $sql);

    }

    /**

     * Called before each db query.

     * @param string $sql

     * @param array|null $params An array of parameters.

     * @param int $type type of query

     * @param mixed $extrainfo driver specific extra information

     * @return void

     */

    protected function query_start($sql, ?array $params, $type, $extrainfo=null) {

        $this->read_slave_query_start($sql, $params, $type, $extrainfo);

        // pgsql driver tends to send debug to output, we do not need that.

        $this->last_error_reporting = error_reporting(0);

    }

    /**

     * Called immediately after each db query.

     * @param mixed db specific result

     * @return void

     */

    protected function query_end($result) {

        // reset original debug level

        error_reporting($this->last_error_reporting);

        try {

            $this->read_slave_query_end($result);

            if ($this->savepointpresent &&

                    !in_array(

                        $this->last_type,

                        [SQL_QUERY_AUX, SQL_QUERY_AUX_READONLY, SQL_QUERY_SELECT],

                        true

                    )) {

                $res = @pg_query($this->pgsql, "RELEASE SAVEPOINT moodle_pg_savepoint; SAVEPOINT moodle_pg_savepoint");

                if ($res) {

                    pg_free_result($res);

                }

            }

        } catch (Exception $e) {

            if ($this->savepointpresent) {

                $res = @pg_query($this->pgsql, "ROLLBACK TO SAVEPOINT moodle_pg_savepoint; SAVEPOINT moodle_pg_savepoint");

                if ($res) {

                    pg_free_result($res);

                }

            }

            throw $e;

        }

    }

    /**

     * Returns database server info array

     * @return array Array containing 'description' and 'version' info

     */

    public function get_server_info(): array {

        if (empty($this->serverinfo)) {

            $this->query_start('--pg_version()', null, SQL_QUERY_AUX);

            $this->serverinfo = pg_version($this->pgsql);

            $this->query_end(true);

        }

        return [

            'description' => $this->serverinfo['server'],

            'version' => $this->serverinfo['server'],

        ];

    }

    /**

     * Returns supported query parameter types

     * @return int bitmask of accepted SQL_PARAMS_*

     */

    protected function allowed_param_types() {

        return SQL_PARAMS_DOLLAR;

    }

    /**

     * Returns last error reported by database engine.

     * @return string error message

     */

    public function get_last_error() {

        return pg_last_error($this->pgsql);

    }

    /**

     * Return tables in database WITHOUT current prefix.

     * @param bool $usecache if true, returns list of cached tables.

     * @return array of table names in lowercase and without prefix

     */

    public function get_tables($usecache=true) {

        if ($usecache and $this->tables !== null) {

            return $this->tables;

        }

        $this->tables = array();

        $prefix = str_replace('_', '|_', $this->prefix);

        $sql = "SELECT c.relname

                  FROM pg_catalog.pg_class c

                  JOIN pg_catalog.pg_namespace as ns ON ns.oid = c.relnamespace

                 WHERE c.relname LIKE '$prefix%' ESCAPE '|'

                       AND c.relkind = 'r'

                       AND (ns.nspname = current_schema() OR ns.oid = pg_my_temp_schema())";

        $this->query_start($sql, null, SQL_QUERY_AUX_READONLY);

        $result = pg_query($this->pgsql, $sql);

        $this->query_end($result);

        if ($result) {

            while ($row = pg_fetch_row($result)) {

                $tablename = reset($row);

                if ($this->prefix !== false && $this->prefix !== '') {

                    if (strpos($tablename, $this->prefix) !== 0) {

                        continue;

                    }

                    $tablename = substr($tablename, strlen($this->prefix));

                }

                $this->tables[$tablename] = $tablename;

            }

            pg_free_result($result);

        }

        return $this->tables;

    }

    /**

     * Constructs 'IN()' or '=' sql fragment

     *

     * Method overriding {@see moodle_database::get_in_or_equal} to be able to use

     * more than 65535 elements in $items array.

     *

     * @param mixed $items A single value or array of values for the expression.

     * @param int $type Parameter bounding type : SQL_PARAMS_QM or SQL_PARAMS_NAMED.

     * @param string $prefix Named parameter placeholder prefix (a unique counter value is appended to each parameter name).

     * @param bool $equal True means we want to equate to the constructed expression, false means we don't want to equate to it.

     * @param mixed $onemptyitems This defines the behavior when the array of items provided is empty. Defaults to false,

     *              meaning throw exceptions. Other values will become part of the returned SQL fragment.

     * @throws coding_exception | dml_exception

     * @return array A list containing the constructed sql fragment and an array of parameters.

     */

    public function get_in_or_equal($items, $type=SQL_PARAMS_QM, $prefix='param', $equal=true, $onemptyitems=false): array {

        // We only interfere if number of items in expression exceeds 16 bit value.

        if (!is_array($items) || count($items) < 65535) {

            return parent::get_in_or_equal($items, $type, $prefix,  $equal, $onemptyitems);

        }

        // Determine the type from the first value. We don't need to be very smart here,

        // it is developer's responsibility to make sure that variable type is matching

        // field type, if not the case, DB engine will hint. Also mixing types won't work

        // here anyway, so we ignore NULL or boolean (unlikely you need 56k values of

        // these types only).

        $cast = is_string(current($items)) ? '::text' : '::bigint';

        if ($type == SQL_PARAMS_QM) {

            if ($equal) {

                $sql = 'IN (VALUES ('.implode('),(', array_fill(0, count($items), '?'.$cast)).'))';

            } else {

                $sql = 'NOT IN (VALUES ('.implode('),(', array_fill(0, count($items), '?'.$cast)).'))';

            }

            $params = array_values($items);

        } else if ($type == SQL_PARAMS_NAMED) {

            if (empty($prefix)) {

                $prefix = 'param';

            }

            $params = [];

            $sql = [];

            foreach ($items as $item) {

                $param = $prefix.$this->inorequaluniqueindex++;

                $params[$param] = $item;

                $sql[] = ':'.$param.$cast;

            }

            if ($equal) {

                $sql = 'IN (VALUES ('.implode('),(', $sql).'))';

            } else {

                $sql = 'NOT IN (VALUES ('.implode('),(', $sql).'))';

            }

        } else {

            throw new dml_exception('typenotimplement');

        }

        return [$sql, $params];

    }

    /**

     * Return table indexes - everything lowercased.

     * @param string $table The table we want to get indexes from.

     * @return array of arrays

     */

    public function get_indexes($table) {

        $indexes = array();

        $tablename = $this->prefix.$table;

        $sql = "SELECT i.*

                  FROM pg_catalog.pg_indexes i

                  JOIN pg_catalog.pg_namespace as ns ON ns.nspname = i.schemaname

                 WHERE i.tablename = '$tablename'

                       AND (i.schemaname = current_schema() OR ns.oid = pg_my_temp_schema())";

        $this->query_start($sql, null, SQL_QUERY_AUX_READONLY);

        $result = pg_query($this->pgsql, $sql);

        $this->query_end($result);

        if ($result) {

            while ($row = pg_fetch_assoc($result)) {

                // The index definition could be generated schema-qualifying the target table name

                // for safety, depending on the pgsql version (CVE-2018-1058).

                if (!preg_match('/CREATE (|UNIQUE )INDEX ([^\s]+) ON (|'.$row['schemaname'].'\.)'.$tablename.' USING ([^\s]+) \(([^\)]+)\)/i', $row['indexdef'], $matches)) {

                    continue;

                }

                if ($matches[5] === 'id') {

                    continue;

                }

                $columns = explode(',', $matches[5]);

                foreach ($columns as $k=>$column) {

                    $column = trim($column);

                    if ($pos = strpos($column, ' ')) {

                        // index type is separated by space

                        $column = substr($column, 0, $pos);

                    }

                    $columns[$k] = $this->trim_quotes($column);

                }

                $indexes[$row['indexname']] = array('unique'=>!empty($matches[1]),

                                              'columns'=>$columns);

            }

            pg_free_result($result);

        }

        return $indexes;

    }

    /**

     * Returns detailed information about columns in table.

     *

     * @param string $table name

     * @return database_column_info[] array of database_column_info objects indexed with column names

     */

    protected function fetch_columns(string $table): array {

        $structure = array();

        $tablename = $this->prefix.$table;

        $sql = "SELECT a.attnum, a.attname AS field, t.typname AS type, a.attlen, a.atttypmod, a.attnotnull, a.atthasdef,

                       CASE WHEN a.atthasdef THEN pg_catalog.pg_get_expr(d.adbin, d.adrelid) ELSE '' END AS adsrc

                  FROM pg_catalog.pg_class c

                  JOIN pg_catalog.pg_namespace as ns ON ns.oid = c.relnamespace

                  JOIN pg_catalog.pg_attribute a ON a.attrelid = c.oid

                  JOIN pg_catalog.pg_type t ON t.oid = a.atttypid

             LEFT JOIN pg_catalog.pg_attrdef d ON (d.adrelid = c.oid AND d.adnum = a.attnum)

                 WHERE relkind = 'r' AND c.relname = '$tablename' AND c.reltype > 0 AND a.attnum > 0

                       AND (ns.nspname = current_schema() OR ns.oid = pg_my_temp_schema())

              ORDER BY a.attnum";

        $this->query_start($sql, null, SQL_QUERY_AUX_READONLY);

        $result = pg_query($this->pgsql, $sql);

        $this->query_end($result);

        if (!$result) {

            return array();

        }

        while ($rawcolumn = pg_fetch_object($result)) {

            $info = new stdClass();

            $info->name = $rawcolumn->field;

            $matches = null;

            if ($rawcolumn->type === 'varchar') {

                $info->type          = 'varchar';

                $info->meta_type     = 'C';

                $info->max_length    = $rawcolumn->atttypmod - 4;

                $info->scale         = null;

                $info->not_null      = ($rawcolumn->attnotnull === 't');

                $info->has_default   = ($rawcolumn->atthasdef === 't');

                if ($info->has_default) {

                    $parts = explode('::', $rawcolumn->adsrc);

                    if (count($parts) > 1) {

                        $info->default_value = reset($parts);

                        $info->default_value = trim($info->default_value, "'");

                    } else {

                        $info->default_value = $rawcolumn->adsrc;

                    }

                } else {

                    $info->default_value = null;

                }

                $info->primary_key   = false;

                $info->binary        = false;

                $info->unsigned      = null;

                $info->auto_increment= false;

                $info->unique        = null;

            } else if (preg_match('/int(\d)/i', $rawcolumn->type, $matches)) {

                $info->type = 'int';

                if (strpos($rawcolumn->adsrc ?? '', 'nextval') === 0) {

                    $info->primary_key   = true;

                    $info->meta_type     = 'R';

                    $info->unique        = true;

                    $info->auto_increment= true;

                    $info->has_default   = false;

                } else {

                    $info->primary_key   = false;

                    $info->meta_type     = 'I';

                    $info->unique        = null;

                    $info->auto_increment= false;

                    $info->has_default   = ($rawcolumn->atthasdef === 't');

                }

                // Return number of decimals, not bytes here.

                if ($matches[1] >= 8) {

                    $info->max_length = 18;

                } else if ($matches[1] >= 4) {

                    $info->max_length = 9;

                } else if ($matches[1] >= 2) {

                    $info->max_length = 4;

                } else if ($matches[1] >= 1) {

                    $info->max_length = 2;

                } else {

                    $info->max_length = 0;

                }

                $info->scale         = null;

                $info->not_null      = ($rawcolumn->attnotnull === 't');

                if ($info->has_default) {

                    // PG 9.5+ uses ::<TYPE> syntax for some defaults.

                    $parts = explode('::', $rawcolumn->adsrc);

                    if (count($parts) > 1) {

                        $info->default_value = reset($parts);

                    } else {

                        $info->default_value = $rawcolumn->adsrc;

                    }

                    $info->default_value = trim($info->default_value, "()'");

                } else {

                    $info->default_value = null;

                }

                $info->binary        = false;

                $info->unsigned      = false;

            } else if ($rawcolumn->type === 'numeric') {

                $info->type = $rawcolumn->type;

                $info->meta_type     = 'N';

                $info->primary_key   = false;

                $info->binary        = false;

                $info->unsigned      = null;

                $info->auto_increment= false;

                $info->unique        = null;

                $info->not_null      = ($rawcolumn->attnotnull === 't');

                $info->has_default   = ($rawcolumn->atthasdef === 't');

                if ($info->has_default) {

                    // PG 9.5+ uses ::<TYPE> syntax for some defaults.

                    $parts = explode('::', $rawcolumn->adsrc);

                    if (count($parts) > 1) {

                        $info->default_value = reset($parts);

                    } else {

                        $info->default_value = $rawcolumn->adsrc;

                    }

                    $info->default_value = trim($info->default_value, "()'");

                } else {

                    $info->default_value = null;

                }

                $info->max_length    = $rawcolumn->atttypmod >> 16;

                $info->scale         = ($rawcolumn->atttypmod & 0xFFFF) - 4;

            } else if (preg_match('/float(\d)/i', $rawcolumn->type, $matches)) {

                $info->type = 'float';

                $info->meta_type     = 'N';

                $info->primary_key   = false;

                $info->binary        = false;

                $info->unsigned      = null;

                $info->auto_increment= false;

                $info->unique        = null;

                $info->not_null      = ($rawcolumn->attnotnull === 't');

                $info->has_default   = ($rawcolumn->atthasdef === 't');

                if ($info->has_default) {

                    // PG 9.5+ uses ::<TYPE> syntax for some defaults.

                    $parts = explode('::', $rawcolumn->adsrc);

                    if (count($parts) > 1) {

                        $info->default_value = reset($parts);

                    } else {

                        $info->default_value = $rawcolumn->adsrc;

                    }

                    $info->default_value = trim($info->default_value, "()'");

                } else {

                    $info->default_value = null;

                }

                // just guess expected number of deciaml places :-(

                if ($matches[1] == 8) {

                    // total 15 digits

                    $info->max_length = 8;

                    $info->scale      = 7;

                } else {

                    // total 6 digits

                    $info->max_length = 4;

                    $info->scale      = 2;

                }

            } else if ($rawcolumn->type === 'text') {

                $info->type          = $rawcolumn->type;

                $info->meta_type     = 'X';

                $info->max_length    = -1;

                $info->scale         = null;

                $info->not_null      = ($rawcolumn->attnotnull === 't');

                $info->has_default   = ($rawcolumn->atthasdef === 't');

                if ($info->has_default) {

                    $parts = explode('::', $rawcolumn->adsrc);

                    if (count($parts) > 1) {

                        $info->default_value = reset($parts);

                        $info->default_value = trim($info->default_value, "'");

                    } else {

                        $info->default_value = $rawcolumn->adsrc;

                    }

                } else {

                    $info->default_value = null;

                }

                $info->primary_key   = false;

                $info->binary        = false;

                $info->unsigned      = null;

                $info->auto_increment= false;

                $info->unique        = null;

            } else if ($rawcolumn->type === 'bytea') {

                $info->type          = $rawcolumn->type;

                $info->meta_type     = 'B';

                $info->max_length    = -1;

                $info->scale         = null;

                $info->not_null      = ($rawcolumn->attnotnull === 't');

                $info->has_default   = false;

                $info->default_value = null;

                $info->primary_key   = false;

                $info->binary        = true;

                $info->unsigned      = null;

                $info->auto_increment= false;

                $info->unique        = null;

            }

            $structure[$info->name] = new database_column_info($info);

        }

        pg_free_result($result);

        return $structure;

    }

    /**

     * Normalise values based in RDBMS dependencies (booleans, LOBs...)

     *

     * @param database_column_info $column column metadata corresponding with the value we are going to normalise

     * @param mixed $value value we are going to normalise

     * @return mixed the normalised value

     */

    protected function normalise_value($column, $value) {

        $this->detect_objects($value);

        if (is_bool($value)) { // Always, convert boolean to int

            $value = (int)$value;

        } else if ($column->meta_type === 'B') {

            if (!is_null($value)) {

                // standard_conforming_strings must be enabled, otherwise pg_escape_bytea() will double escape

                // \ and produce data errors.  This is set on the connection.

                $value = pg_escape_bytea($this->pgsql, $value);

            }

        } else if ($value === '') {

            if ($column->meta_type === 'I' or $column->meta_type === 'F' or $column->meta_type === 'N') {

                $value = 0; // prevent '' problems in numeric fields

            }

        }

        return $value;

    }

    /**

     * Is db in unicode mode?

     * @return bool

     */

    public function setup_is_unicodedb() {

        // Get PostgreSQL server_encoding value

        $sql = 'SHOW server_encoding';

        $this->query_start($sql, null, SQL_QUERY_AUX_READONLY);

        $result = pg_query($this->pgsql, $sql);

        $this->query_end($result);

        if (!$result) {

            return false;

        }

        $rawcolumn = pg_fetch_object($result);

        $encoding = $rawcolumn->server_encoding;

        pg_free_result($result);

        return (strtoupper($encoding) == 'UNICODE' || strtoupper($encoding) == 'UTF8');

    }

    /**

     * Do NOT use in code, to be used by database_manager only!

     * @param string|array $sql query

     * @param array|null $tablenames an array of xmldb table names affected by this request.

     * @return bool true

     * @throws ddl_change_structure_exception A DDL specific exception is thrown for any errors.

     */

    public function change_database_structure($sql, $tablenames = null) {

        $this->get_manager(); // Includes DDL exceptions classes ;-)

        if (is_array($sql)) {

            $sql = implode("\n;\n", $sql);

        }

        if (!$this->is_transaction_started()) {

            // It is better to do all or nothing, this helps with recovery...

            $sql = "BEGIN ISOLATION LEVEL SERIALIZABLE;\n$sql\n; COMMIT";

        }

        try {

            $this->query_start($sql, null, SQL_QUERY_STRUCTURE);

            $result = pg_query($this->pgsql, $sql);

            $this->query_end($result);

            pg_free_result($result);

        } catch (ddl_change_structure_exception $e) {

            if (!$this->is_transaction_started()) {

                $result = @pg_query($this->pgsql, "ROLLBACK");

                @pg_free_result($result);

            }

            $this->reset_caches($tablenames);

            throw $e;

        }

        $this->reset_caches($tablenames);

        return true;

    }

    /**

     * Execute general sql query. Should be used only when no other method suitable.

     * Do NOT use this to make changes in db structure, use database_manager methods instead!

     * @param string $sql query

     * @param array $params query parameters

     * @return bool true

     * @throws dml_exception A DML specific exception is thrown for any errors.

     */

    public function execute($sql, array $params=null) {

        list($sql, $params, $type) = $this->fix_sql_params($sql, $params);

        if (strpos($sql, ';') !== false) {

            throw new coding_exception('moodle_database::execute() Multiple sql statements found or bound parameters not used properly in query!');

        }

        $this->query_start($sql, $params, SQL_QUERY_UPDATE);

        $result = pg_query_params($this->pgsql, $sql, $params);

        $this->query_end($result);

        pg_free_result($result);

        return true;

    }

    /**

     * Get a number of records as a moodle_recordset using a SQL statement.

     *

     * Since this method is a little less readable, use of it should be restricted to

     * code where it's possible there might be large datasets being returned.  For known

     * small datasets use get_records_sql - it leads to simpler code.

     *

     * The return type is like:

     * @see function get_recordset.

     *

     * @param string $sql the SQL select query to execute.

     * @param array $params array of sql parameters

     * @param int $limitfrom return a subset of records, starting at this point (optional, required if $limitnum is set).

     * @param int $limitnum return a subset comprising this many records (optional, required if $limitfrom is set).

     * @return moodle_recordset instance

     * @throws dml_exception A DML specific exception is thrown for any errors.

     */

    public function get_recordset_sql($sql, array $params=null, $limitfrom=0, $limitnum=0) {

        list($limitfrom, $limitnum) = $this->normalise_limit_from_num($limitfrom, $limitnum);

        if ($limitnum) {

            $sql .= " LIMIT $limitnum";

        }

        if ($limitfrom) {

            $sql .= " OFFSET $limitfrom";

        }

        list($sql, $params, $type) = $this->fix_sql_params($sql, $params);

        // For any query that doesn't explicitly specify a limit, we must use cursors to stop it

        // loading the entire thing (unless the config setting is turned off).

        $usecursors = !$limitnum && ($this->get_fetch_buffer_size() > 0);

        if ($usecursors) {

            // Work out the cursor unique identifer. This is based on a simple count used which

            // should be OK because the identifiers only need to be unique within the current

            // transaction.

            $this->cursorcount++;

            $cursorname = 'crs' . $this->cursorcount;

            // Do the query to a cursor.

            $sql = 'DECLARE ' . $cursorname . ' NO SCROLL CURSOR WITH HOLD FOR ' . $sql;

        } else {

            $cursorname = '';

        }

        $this->query_start($sql, $params, SQL_QUERY_SELECT);

        $result = pg_query_params($this->pgsql, $sql, $params);

        $this->query_end($result);

        if ($usecursors) {

            pg_free_result($result);

            $result = null;

        }

        return new pgsql_native_moodle_recordset($result, $this, $cursorname);

    }

    /**

     * Gets size of fetch buffer used for recordset queries.

     *

     * If this returns 0 then cursors will not be used, meaning recordset queries will occupy enough

     * memory as needed for the Postgres library to hold the entire query results in memory.

     *

     * @return int Fetch buffer size or 0 indicating not to use cursors

     */

    protected function get_fetch_buffer_size() {

        if (array_key_exists('fetchbuffersize', $this->dboptions)) {

            return (int)$this->dboptions['fetchbuffersize'];

        } else {

            return self::DEFAULT_FETCH_BUFFER_SIZE;

        }

    }

    /**

     * Retrieves data from cursor. For use by recordset only; do not call directly.

     *

     * Return value contains the next batch of Postgres data, and a boolean indicating if this is

     * definitely the last batch (if false, there may be more)

     *

     * @param string $cursorname Name of cursor to read from

     * @return array Array with 2 elements (next data batch and boolean indicating last batch)

     */

    public function fetch_from_cursor($cursorname) {

        $count = $this->get_fetch_buffer_size();

        $sql = 'FETCH ' . $count . ' FROM ' . $cursorname;

        $this->query_start($sql, [], SQL_QUERY_AUX);

        $result = pg_query($this->pgsql, $sql);

        $last = pg_num_rows($result) !== $count;

        $this->query_end($result);

        return [$result, $last];

    }

    /**

     * Closes a cursor. For use by recordset only; do not call directly.

     *

     * @param string $cursorname Name of cursor to close

     * @return bool True if we actually closed one, false if the transaction was cancelled

     */

    public function close_cursor($cursorname) {

        // If the transaction got cancelled, then ignore this request.

        $sql = 'CLOSE ' . $cursorname;

        $this->query_start($sql, [], SQL_QUERY_AUX);

        $result = pg_query($this->pgsql, $sql);

        $this->query_end($result);

        if ($result) {

            pg_free_result($result);

        }

        return true;

    }

    /**

     * A faster version of pg_field_type

     *

     * The pg_field_type function in the php postgres driver internally makes an sql call

     * to get the list of field types which it statically caches only for a single request.

     * This wraps it in a cache keyed by oid to avoid these DB calls on every request.

     *

     * @param resource|PgSql\Result $result

     * @param int $fieldnumber

     * @return string Field type

     */

    public function pg_field_type($result, int $fieldnumber) {

        static $map;

        $cache = $this->get_metacache();

        // Getting the oid doesn't make an internal query.

        $oid = pg_field_type_oid($result, $fieldnumber);