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MDL-37734 use prefetching workaround for MARS transaction problems

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commit 1d657914670d9f7e9c4aa4b01b3a9603907c28a5 1 parent b05659d
@skodak skodak authored
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23 lib/dml/sqlsrv_native_moodle_database.php
@@ -41,6 +41,8 @@ class sqlsrv_native_moodle_database extends moodle_database {
protected $last_error_reporting; // To handle SQL*Server-Native driver default verbosity
protected $temptables; // Control existing temptables (sqlsrv_moodle_temptables object)
protected $collation; // current DB collation cache
+ /** @var array list of open recordsets */
+ protected $recordsets = array();
/**
* Constructor - instantiates the database, specifying if it's external (connect to other systems) or no (Moodle DB)
@@ -789,7 +791,20 @@ public function get_recordset_sql($sql, array $params = null, $limitfrom = 0, $l
* @return sqlsrv_native_moodle_recordset
*/
protected function create_recordset($result) {
- return new sqlsrv_native_moodle_recordset($result);
+ $rs = new sqlsrv_native_moodle_recordset($result, $this);
+ $this->recordsets[] = $rs;
+ return $rs;
+ }
+
+ /**
+ * Do not use outside of recordset class.
+ * @internal
+ * @param sqlsrv_native_moodle_recordset $rs
+ */
+ public function recordset_closed(sqlsrv_native_moodle_recordset $rs) {
+ if ($key = array_search($rs, $this->recordsets, true)) {
+ unset($this->recordsets[$key]);
+ }
}
/**
@@ -1363,6 +1378,12 @@ public function release_session_lock($rowid) {
* @return void
*/
protected function begin_transaction() {
+ // Recordsets do not work well with transactions in SQL Server,
+ // let's prefetch the recordsets to memory to work around these problems.
+ foreach ($this->recordsets as $rs) {
+ $rs->transaction_starts();
+ }
+
$this->query_start('native sqlsrv_begin_transaction', NULL, SQL_QUERY_AUX);
$result = sqlsrv_begin_transaction($this->sqlsrv);
$this->query_end($result);
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66 lib/dml/sqlsrv_native_moodle_recordset.php
@@ -31,9 +31,49 @@ class sqlsrv_native_moodle_recordset extends moodle_recordset {
protected $rsrc;
protected $current;
- public function __construct($rsrc) {
- $this->rsrc = $rsrc;
+ /** @var array recordset buffer */
+ protected $buffer = null;
+
+ /** @var sqlsrv_native_moodle_database */
+ protected $db;
+
+ public function __construct($rsrc, sqlsrv_native_moodle_database $db) {
+ $this->rsrc = $rsrc;
$this->current = $this->fetch_next();
+ $this->db = $db;
+ }
+
+ /**
+ * Inform existing open recordsets that transaction
+ * is starting, this works around MARS problem described
+ * in MDL-37734.
+ */
+ public function transaction_starts() {
+ if ($this->buffer !== null) {
+ $this->unregister();
+ return;
+ }
+ if (!$this->rsrc) {
+ $this->unregister();
+ return;
+ }
+ // This might eat memory pretty quickly...
+ raise_memory_limit('2G');
+ $this->buffer = array();
+
+ while($next = $this->fetch_next()) {
+ $this->buffer[] = $next;
+ }
+ }
+
+ /**
+ * Unregister recordset from the global list of open recordsets.
+ */
+ private function unregister() {
+ if ($this->db) {
+ $this->db->recordset_closed($this);
+ $this->db = null;
+ }
}
public function __destruct() {
@@ -41,10 +81,18 @@ public function __destruct() {
}
private function fetch_next() {
- if ($row = sqlsrv_fetch_array($this->rsrc, SQLSRV_FETCH_ASSOC)) {
- unset($row['sqlsrvrownumber']);
- $row = array_change_key_case($row, CASE_LOWER);
+ if (!$this->rsrc) {
+ return false;
}
+ if (!$row = sqlsrv_fetch_array($this->rsrc, SQLSRV_FETCH_ASSOC)) {
+ sqlsrv_free_stmt($this->rsrc);
+ $this->rsrc = null;
+ $this->unregister();
+ return false;
+ }
+
+ unset($row['sqlsrvrownumber']);
+ $row = array_change_key_case($row, CASE_LOWER);
return $row;
}
@@ -62,7 +110,11 @@ public function key() {
}
public function next() {
- $this->current = $this->fetch_next();
+ if ($this->buffer === null) {
+ $this->current = $this->fetch_next();
+ } else {
+ $this->current = array_shift($this->buffer);
+ }
}
public function valid() {
@@ -75,5 +127,7 @@ public function close() {
$this->rsrc = null;
}
$this->current = null;
+ $this->buffer = null;
+ $this->unregister();
}
}
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