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dmllib: introducing the rcache_* functions for record cache handling
Abstracted Sam's initial work with $record_cache into a series of functions that abstract things _just enough_ that we can use an internal in-memory-array implementation or something that is shared across processes, like memcached or the turckmmcache/eaccelerator caches. Also - added hit/miss stats tracking and reporting - removed max entries limiting as it was buggy - var names mismatches and not counting unset()s
This commit is contained in:
martinlanghoff
parent
adb61bc203
commit
6c2f585f85
201
lib/dmllib.php
201
lib/dmllib.php
@ -39,8 +39,11 @@
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$empty_rs_cache = array(); // Keeps copies of the recordsets used in one invocation
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$metadata_cache = array(); // Keeps copies of the MetaColumns() for each table used in one invocations
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$record_cache = array(); // Keeps copies of all simple get_record results from one invocation
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$record_cache_size = 0; // Count of get_record results stored in this invocation
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$rcache = new StdClass; // Cache simple get_record results
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$rcache->data = array();
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$rcache->hits = 0;
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$rcache->misses = 0;
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/// FUNCTIONS FOR DATABASE HANDLING ////////////////////////////////
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@ -379,15 +382,16 @@ function count_records_sql($sql) {
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*/
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function get_record($table, $field1, $value1, $field2='', $value2='', $field3='', $value3='', $fields='*') {
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global $CFG, $record_cache, $record_cache_count;
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global $CFG;
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// Check to see whether this record is eligible for caching (fields=*, only condition is id)
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$docache = false;
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if (!empty($CFG->enablerecordcache) && $field1=='id' && !$field2 && !$field3 && $fields=='*') {
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$docache = true;
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// If it's in the cache, return it
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if (!empty($record_cache[$table][$value1])) {
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return $record_cache[$table][$value1];
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$cached = rcache_get($table, $value1);
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if (!empty($cached)) {
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return $cached;
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}
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}
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@ -395,13 +399,10 @@ function get_record($table, $field1, $value1, $field2='', $value2='', $field3=''
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$record = get_record_sql('SELECT '.$fields.' FROM '. $CFG->prefix . $table .' '. $select);
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// If we're caching records, store this one (supposing we got something - we don't cache failures)
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if ($record && $docache && $record_cache_count<$CFG->enablerecordcache) {
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$record_cache[$table][$value1] = $record;
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// We only cache records up to a limit. This is to prevent memory usage becoming
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// unreasonably high for pages which do things like, load every student record in
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// a course, or some such.
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$record_cache_count++;
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// If we're caching records, store this one
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// (supposing we got something - we don't cache failures)
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if ($record && $docache) {
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rcache_set($table, $value1, $record);
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}
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return $record;
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@ -1036,26 +1037,19 @@ function get_fieldset_sql($sql) {
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*/
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function set_field($table, $newfield, $newvalue, $field1, $value1, $field2='', $value2='', $field3='', $value3='') {
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global $CFG, $record_cache;
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global $CFG;
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// Clear record_cache based on the parameters passed (individual record or whole table)
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// Clear record_cache based on the parameters passed
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// (individual record or whole table)
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if (!empty($CFG->enablerecordcache)) {
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if ($field1 == 'id') {
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if (isset($record_cache[$table][$value1])) {
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unset($record_cache[$table][$value1]);
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}
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rcache_unset($table, $value1);
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} else if ($field2 == 'id') {
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if (isset($record_cache[$table][$value2])) {
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unset($record_cache[$table][$value2]);
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}
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rcache_unset($table, $value1);
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} else if ($field3 == 'id') {
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if (isset($record_cache[$table][$value3])) {
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unset($record_cache[$table][$value3]);
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}
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rcache_unset($table, $value1);
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} else {
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if (isset($record_cache[$table])) {
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unset($record_cache[$table]);
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}
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rcache_unset_table($table);
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}
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}
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@ -1078,7 +1072,7 @@ function set_field($table, $newfield, $newvalue, $field1, $value1, $field2='', $
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*/
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function set_field_select($table, $newfield, $newvalue, $select, $localcall = false) {
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global $db, $CFG, $record_cache;
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global $db, $CFG;
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if (defined('MDL_PERFDB')) { global $PERF ; $PERF->dbqueries++; };
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@ -1087,11 +1081,10 @@ function set_field_select($table, $newfield, $newvalue, $select, $localcall = fa
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$select = 'WHERE ' . $select;
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}
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// Clear record_cache based on the parameters passed (individual record or whole table)
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// Clear record_cache based on the parameters passed
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// (individual record or whole table)
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if (!empty($CFG->enablerecordcache)) {
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if (isset($record_cache[$table])) {
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unset($record_cache[$table]);
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}
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rcache_unset_table($table);
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}
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}
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@ -1147,26 +1140,19 @@ function set_field_select($table, $newfield, $newvalue, $select, $localcall = fa
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*/
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function delete_records($table, $field1='', $value1='', $field2='', $value2='', $field3='', $value3='') {
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global $db, $CFG, $record_cache;
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global $db, $CFG;
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// Clear record_cache based on the parameters passed (individual record or whole table)
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// Clear record_cache based on the parameters passed
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// (individual record or whole table)
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if (!empty($CFG->enablerecordcache)) {
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if ($field1 == 'id') {
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if (isset($record_cache[$table][$value1])) {
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unset($record_cache[$table][$value1]);
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}
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rcache_unset($table, $value1);
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} else if ($field2 == 'id') {
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if (isset($record_cache[$table][$value2])) {
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unset($record_cache[$table][$value2]);
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}
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rcache_unset($table, $value2);
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} else if ($field3 == 'id') {
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if (isset($record_cache[$table][$value3])) {
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unset($record_cache[$table][$value3]);
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}
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rcache_unset($table, $value3);
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} else {
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if (isset($record_cache[$table])) {
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unset($record_cache[$table]);
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}
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rcache_unset_table($table);
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}
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}
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@ -1189,11 +1175,11 @@ function delete_records($table, $field1='', $value1='', $field2='', $value2='',
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*/
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function delete_records_select($table, $select='') {
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global $CFG, $db, $record_cache;
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global $CFG, $db;
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// Clear record_cache (whole table)
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if (!empty($CFG->enablerecordcache) && isset($record_cache[$table])) {
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unset($record_cache[$table]);
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if (!empty($CFG->enablerecordcache)) {
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rcache_unset_table($table);
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}
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if (defined('MDL_PERFDB')) { global $PERF ; $PERF->dbqueries++; };
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@ -1401,15 +1387,15 @@ function insert_record($table, $dataobject, $returnid=true, $primarykey='id') {
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*/
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function update_record($table, $dataobject) {
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global $db, $CFG, $record_cache;
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global $db, $CFG;
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if (! isset($dataobject->id) ) {
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return false;
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}
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// Remove this record from record cache since it will change
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if (!empty($CFG->enablerecordcache) && isset($record_cache[$table][$dataobject->id])) {
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unset($record_cache[$table][$dataobject->id]);
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if (!empty($CFG->enablerecordcache)) {
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rcache_unset($table, $dataobject->id);
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}
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/// Temporary hack as part of phasing out all access to obsolete user tables XXX
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@ -2079,4 +2065,117 @@ function db_update_lobs ($table, $sqlcondition, &$clobs, &$blobs) {
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return $status;
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}
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function rcache_set($table, $id, $rec) {
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global $CFG, $rcache;
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$rcache->data[$table][$id] = $rec;
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return true;
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}
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function rcache_unset($table, $id) {
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global $CFG, $rcache;
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if (isset($rcache->data[$table][$id])) {
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unset($rcache->data[$table][$id]);
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}
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return true;
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}
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/**
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* Get cached record if available. ONLY use if you
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* are trying to get the cached record and will NOT
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* fetch it yourself if not cached.
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*
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* Use rcache_getforfill() if you are going to fetch
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* the record if not cached...
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*
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* This function is private and must not be used outside dmllib at all
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*
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* @param $table string
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* @param $id integer
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* @return mixed object-like record on cache hit, false otherwise
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*/
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function rcache_get($table, $id) {
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global $CFG, $rcache;
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if (isset($rcache->data[$table][$id])) {
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$rcache->hits++;
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return $rcache->data[$table][$id];
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} else {
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$rcache->misses++;
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return false;
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}
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}
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/**
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* In the simple case, this function will
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* get cached record if available. If the record
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* is not available, it will try to get an exclusive
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* lock that announces that this process will fetch
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* the record and populate the cache.
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*
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* If we fail to get the lock -- this means another
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* process is going to fetch the rec and fill the cache
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* so we wait (block) for a few microseconds while we wait for
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* the cache to be filled or the lock to timeout.
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*
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* If you get a false from this call, you _must_ fetch the
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* rec from DB and populate the cache ASAP or indicate that
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* you won't by calling rcache_releaseforfill().
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*
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* This technique forces serialisation and so helps deal
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* with thundering herd scenarios where a lot of clients
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* ask the for the same idempotent (and costly) operation.
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* The implementation is based on suggestions in this message
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* http://marc.theaimsgroup.com/?l=git&m=116562052506776&w=2
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*
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* This function is private and must not be used outside dmllib at all
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*
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* @param $table string
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* @param $id integer
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* @return mixed object-like record on cache hit, false otherwise
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*/
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function rcache_getforfill($table, $id) {
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global $CFG, $rcache;
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return rcache_get($table, $id);
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}
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/**
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* Release the exclusive lock obtained by
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* rcache_getforfill(). See rcache_getforfill()
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* for more details.
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*
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* This function is private and must not be used outside dmllib at all
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*
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* @param $table string
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* @param $id integer
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* @return bool
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*/
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function rcache_releaseforfill($table, $id) {
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global $CFG, $rcache;
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return true;
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}
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/**
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* Remove or invalidate all rcache entries related to
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* a table. Not all caching mechanisms cluster entries
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* by table so in those cases we use alternative strategies.
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*
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* This function is private and must not be used outside dmllib at all
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*
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* @param $table string the table to invalidate records for
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* @return bool
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*/
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function rcache_unset_table ($table) {
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global $CFG, $rcache;
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if (isset($rcache->data[$table])) {
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unset($rcache->data[$table]);
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}
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return true;
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}
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?>
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@ -6466,7 +6466,7 @@ function array_is_nested($array) {
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***
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**/
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function get_performance_info() {
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global $CFG, $PERF;
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global $CFG, $PERF, $rcache;
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$info = array();
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$info['html'] = ''; // holds userfriendly HTML representation
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@ -6529,10 +6529,17 @@ function get_performance_info() {
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if (!empty($server_load)) {
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$info['serverload'] = $server_load;
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$info['html'] .= '<span class="serverload">Load average: '.$info['serverload'].'</span> ';
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$info['txt'] .= 'serverload: '.$info['serverload'];
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$info['txt'] .= "serverload: {$info['serverload']} ";
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}
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if (isset($rcache->hits) && isset($rcache->misses)) {
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$info['rcachehits'] = $rcache->hits;
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$info['rcachemisses'] = $rcache->misses;
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$info['html'] .= '<span class="rcache">Record cache hit/miss ratio : '.
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($rcache->hits / $rcache->misses) . "({$rcache->hits}/{$rcache->misses})</span> ";
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$info['txt'] .= 'rcache: '. ($rcache->hits / $rcache->misses) .
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"({$rcache->hits}/{$rcache->misses}) ";
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}
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$info['html'] = '<div class="performanceinfo">'.$info['html'].'</div>';
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return $info;
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}
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