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MDL-66327 pgsql DML: Update get_records_sql to consume less memory

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It's more memory efficient to use `pg_fetch_assoc` for each row than to
call `pg_fetch_all` and release memory immediately. This is because we
can treat the assoc fetch like an iterator and it only fetches the
current record into memory one at a time, whilst the all fetch fetches
all records and never unsets them. Attempting to unset them is extremely
time consuming.
This commit is contained in:
Andrew Nicols 2019-08-08 14:03:41 +08:00
parent 414eca8923
commit 66fa73d84e
1 changed files with 12 additions and 18 deletions
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30
lib/dml/pgsql_native_moodle_database.php
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@ -842,8 +842,7 @@ class pgsql_native_moodle_database extends moodle_database {
* @return array of objects, or empty array if no records were found
* @throws dml_exception A DML specific exception is thrown for any errors.
*/
public function get_records_sql($sql, array $params=null, $limitfrom=0, $limitnum=0) {
public function get_records_sql($sql, array $params = null, $limitfrom = 0, $limitnum = 0) {
list($limitfrom, $limitnum) = $this->normalise_limit_from_num($limitfrom, $limitnum);
if ($limitnum) {
@ -868,24 +867,19 @@ class pgsql_native_moodle_database extends moodle_database {
}
}
$rows = pg_fetch_all($result);
pg_free_result($result);
$return = array();
if ($rows) {
foreach ($rows as $row) {
$id = reset($row);
if ($blobs) {
foreach ($blobs as $blob) {
$row[$blob] = ($row[$blob] !== null ? pg_unescape_bytea($row[$blob]) : null);
}
$return = [];
while ($row = pg_fetch_assoc($result)) {
$id = reset($row);
if ($blobs) {
foreach ($blobs as $blob) {
$row[$blob] = ($row[$blob] !== null ? pg_unescape_bytea($row[$blob]) : null);
}
if (isset($return[$id])) {
$colname = key($row);
debugging("Did you remember to make the first column something unique in your call to get_records? Duplicate value '$id' found in column '$colname'.", DEBUG_DEVELOPER);
}
$return[$id] = (object)$row;
}
if (isset($return[$id])) {
$colname = key($row);
debugging("Did you remember to make the first column something unique in your call to get_records? Duplicate value '$id' found in column '$colname'.", DEBUG_DEVELOPER);
}
$return[$id] = (object) $row;
}
return $return;