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SQLiteL1: Initial Implementation #62

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Merged
joshkoenig merged 1 commit into from
Nov 21, 2016
Merged

SQLiteL1: Initial Implementation #62

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1 change: 0 additions & 1 deletion src/L2.php
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,5 @@ abstract public function set($pool, Address $address, $value = null, $expiration
abstract public function delete($pool, Address $address);
abstract public function deleteTag(L1 $l1, $tag);
abstract public function getAddressesForTag($tag);
abstract public function collectGarbage($item_limit = null);
abstract public function countGarbage();
}
5 changes: 5 additions & 0 deletions src/LX.php
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Expand Up @@ -35,4 +35,9 @@ public function exists(Address $address)
$value = $this->get($address);
return !is_null($value);
}

public function collectGarbage($item_limit = null)
{
return 0;
}
}
294 changes: 294 additions & 0 deletions src/SQLiteL1.php
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Original file line number Diff line number Diff line change
@@ -0,0 +1,294 @@
<?php

namespace LCache;

class SQLiteL1 extends L1
{
/** @var \PDO */
private $dbh;

/** @var string */
private $statusKeyHits;

/** @var string */
private $statusKeyMisses;

/** @var string */
private $statusKeyLastAppliedEventId;

protected static function tableExists(\PDO $dbh, $table_name)
{
try {
$dbh->query('SELECT 1 FROM ' . $table_name . ' LIMIT 1');
} catch (\PDOException $e) {
if (in_array($e->getCode(), ['42S02', 'HY000'])) {
return false;
}
// Rethrow anything else.
// @codeCoverageIgnoreStart
throw $e;
// @codeCoverageIgnoreEnd
}
return true;
}

protected static function initializeSchema(\PDO $dbh)
{
if (!self::tableExists($dbh, 'entries')) {
$dbh->exec('CREATE TABLE IF NOT EXISTS entries("address" TEXT PRIMARY KEY, "value" BLOB, "expiration" INTEGER, "created" INTEGER, "event_id" INTEGER NOT NULL DEFAULT 0, "reads" INTEGER NOT NULL DEFAULT 0, "writes" INTEGER NOT NULL DEFAULT 0)');
$dbh->exec('CREATE INDEX IF NOT EXISTS expiration ON entries ("expiration")');
}
}

protected static function getDatabaseHandle($pool)
{
$path = join(DIRECTORY_SEPARATOR, array(sys_get_temp_dir(), 'lcache-' . $pool));
$dbh = new \PDO('sqlite:' . $path . '.sqlite3');
$dbh->setAttribute(\PDO::ATTR_ERRMODE, \PDO::ERRMODE_EXCEPTION);
$dbh->exec('PRAGMA synchronous = OFF');
$dbh->exec('PRAGMA foreign_keys = ON');
self::initializeSchema($dbh);
return $dbh;
}

public function __construct($pool = null)
{
parent::__construct($pool);
$this->dbh = self::getDatabaseHandle($this->pool);

$this->statusKeyHits = 'lcache_status:' . $this->pool . ':hits';
$this->statusKeyMisses = 'lcache_status:' . $this->pool . ':misses';
$this->statusKeyLastAppliedEventId = 'lcache_status:' . $this->pool . ':last_applied_event_id';
}

protected function pruneExpiredEntries()
{
$sth = $this->dbh->prepare('DELETE FROM entries WHERE expiration < :now');
$sth->bindValue(':now', $_SERVER['REQUEST_TIME'], \PDO::PARAM_INT);
try {
$sth->execute();
// @codeCoverageIgnoreStart
} catch (\PDOException $e) {
$text = 'LCache SQLiteL1: Pruning Failed: ' . $e->getMessage();
trigger_error($text, E_USER_WARNING);
return false;
}
// @codeCoverageIgnoreEnd
return $sth->rowCount();
}

public function __destruct()
{
$this->pruneExpiredEntries();
}

public function collectGarbage($item_limit = null)
{
$items = $this->pruneExpiredEntries();
return $items;
}

public function getKeyOverhead(Address $address)
{
$sth = $this->dbh->prepare('SELECT "reads", "writes" FROM entries WHERE "address" = :address');
$sth->bindValue(':address', $address->serialize(), \PDO::PARAM_STR);
$sth->execute();
$result = $sth->fetchObject();

if ($result === false) {
return 0;
}

return $result->writes - $result->reads;
}

public function setWithExpiration($event_id, Address $address, $value, $created, $expiration = null)
{
$serialized_value = null;
if (!is_null($value)) {
$serialized_value = serialize($value);
}

$sth = $this->dbh->prepare('INSERT OR IGNORE INTO entries ("address", "value", "expiration", "created", "event_id", "writes") VALUES (:address, :value, :expiration, :created, :event_id, 1)');
$sth->bindValue(':address', $address->serialize(), \PDO::PARAM_STR);
$sth->bindValue(':value', $serialized_value, \PDO::PARAM_LOB);
$sth->bindValue(':expiration', $expiration, \PDO::PARAM_INT);
$sth->bindValue(':created', $created, \PDO::PARAM_INT);
$sth->bindValue(':event_id', $event_id, \PDO::PARAM_INT);
$sth->execute();

// A count of zero means a conflict during the insertion. Update in a way
// that avoids stomping on newer writes.
if ($sth->rowCount() === 0) {
$bump_writes = ', "writes" = "writes" + 1';
// Don't bump write counts for negative cache entries.
if (is_null($value)) {
$bump_writes = '';
}

// Always allow overwrites of event ID zero so when there's been a
// read (which creates a row with a read count of one) and then we
// still miss L2 (which creates an L1 tombstone here), the update
// goes through.
$sth = $this->dbh->prepare('UPDATE entries SET "value" = :value, "expiration" = :expiration, "created" = :created, "event_id" = :event_id ' . $bump_writes . ' WHERE "address" = :address AND ("event_id" < :event_id OR "event_id" = 0)');
$sth->bindValue(':address', $address->serialize(), \PDO::PARAM_STR);
$sth->bindValue(':value', $serialized_value, \PDO::PARAM_LOB);
$sth->bindValue(':expiration', $expiration, \PDO::PARAM_INT);
$sth->bindValue(':created', $created, \PDO::PARAM_INT);
$sth->bindValue(':event_id', $event_id, \PDO::PARAM_INT);
$sth->execute();
}

return true;
}

public function exists(Address $address)
{
$sth = $this->dbh->prepare('SELECT COUNT(*) AS existing FROM entries WHERE "address" = :address AND ("expiration" >= :now OR "expiration" IS NULL) AND "value" IS NOT NULL');
$sth->bindValue(':address', $address->serialize(), \PDO::PARAM_STR);
$sth->bindValue(':now', $_SERVER['REQUEST_TIME'], \PDO::PARAM_INT);
$sth->execute();
$result = $sth->fetchObject();
return $result->existing > 0;
}

public function isNegativeCache(Address $address)
{
$sth = $this->dbh->prepare('SELECT COUNT(*) AS entry_count FROM entries WHERE "address" = :address AND ("expiration" >= :now OR "expiration" IS NULL) AND "value" IS NULL');
$sth->bindValue(':address', $address->serialize(), \PDO::PARAM_STR);
$sth->bindValue(':now', $_SERVER['REQUEST_TIME'], \PDO::PARAM_INT);
$sth->execute();
$result = $sth->fetchObject();
return ($result->entry_count > 0);
}

/**
* @codeCoverageIgnore
*/
public function debugDumpState()
{
echo PHP_EOL . PHP_EOL . 'Entries:' . PHP_EOL;
$sth = $this->dbh->prepare('SELECT * FROM "entries" ORDER BY "address"');
$sth->execute();
while ($event = $sth->fetchObject()) {
print_r($event);
}
echo PHP_EOL;
}

public function getEntry(Address $address)
{
$sth = $this->dbh->prepare('SELECT "value", "expiration", "reads", "writes", "created" FROM entries WHERE "address" = :address AND ("expiration" >= :now OR "expiration" IS NULL)');
$sth->bindValue(':address', $address->serialize(), \PDO::PARAM_STR);
$sth->bindValue(':now', $_SERVER['REQUEST_TIME'], \PDO::PARAM_INT);
$sth->execute();
$entry = $sth->fetchObject();

// If there are under 10X reads versus writes, bump the read count. We
// do this to simultaneously track useful overhead data but not unnecessarily
// record reads after they massively outweigh writes for an address.
// @TODO: Make this adapt to overhead thresholds.
if ($entry === false || $entry->reads < 10 * $entry->writes || $entry->reads < 10) {
$sth = $this->dbh->prepare('UPDATE entries SET "reads" = "reads" + 1 WHERE "address" = :address');
$sth->bindValue(':address', $address->serialize(), \PDO::PARAM_STR);
$sth->execute();
if ($sth->rowCount() === 0) {
// Use a zero expiration so this row is only used for counts, not negative caching.
// Use the default event ID of zero to ensure any writes win over this stub.
$sth = $this->dbh->prepare('INSERT OR IGNORE INTO entries ("address", "expiration", "reads") VALUES (:address, 0, 1)');
$sth->bindValue(':address', $address->serialize(), \PDO::PARAM_STR);
$sth->execute();
}
}

if ($entry === false) {
$this->recordMiss();
return null;
}

// Unserialize non-null values.
if (!is_null($entry->value)) {
$entry->value = unserialize($entry->value);
}

$this->recordHit();
return $entry;
}

public function delete($event_id, Address $address)
{
if ($address->isEntireCache() || $address->isEntireBin()) {
$pattern = $address->serialize() . '%';
$sth = $this->dbh->prepare('DELETE FROM entries WHERE "address" LIKE :pattern');
$sth->bindValue('pattern', $pattern, \PDO::PARAM_STR);
$sth->execute();
return true;
}

$sth = $this->dbh->prepare('DELETE FROM entries WHERE "address" = :address AND event_id < :event_id');
$sth->bindValue(':address', $address->serialize(), \PDO::PARAM_STR);
$sth->bindValue(':event_id', $event_id, \PDO::PARAM_INT);
$sth->execute();
return true;
}

// @TODO: Update hit/miss functions to either record nothing or fall back
// to SQLite storage if APCu is not available.

protected function recordHit()
{
$success = false; // Make Scrutinizer happy.
apcu_inc($this->statusKeyHits, 1, $success);
if (!$success) {
// @TODO: Remove this fallback when we drop APCu 4.x support.
// @codeCoverageIgnoreStart
// Ignore coverage because (1) it's tested with other code and
// (2) APCu 5.x does not use it.
apcu_store($this->statusKeyHits, 1);
// @codeCoverageIgnoreEnd
}
}

protected function recordMiss()
{
$success = false; // Make Scrutinizer happy.
apcu_inc($this->statusKeyMisses, 1, $success);
if (!$success) {
// @TODO: Remove this fallback when we drop APCu 4.x support.
// @codeCoverageIgnoreStart
// Ignore coverage because (1) it's tested with other code and
// (2) APCu 5.x does not use it.
apcu_store($this->statusKeyMisses, 1);
// @codeCoverageIgnoreEnd
}
}

public function getHits()
{
$value = apcu_fetch($this->statusKeyHits);
return $value ? $value : 0;
}

public function getMisses()
{
$value = apcu_fetch($this->statusKeyMisses);
return $value ? $value : 0;
}

// @TODO: Update event ID tracking to either record fall back
// to SQLite storage if APCu is not available.

public function getLastAppliedEventID()
{
$value = apcu_fetch($this->statusKeyLastAppliedEventId);
if ($value === false) {
$value = null;
}
return $value;
}

public function setLastAppliedEventID($eid)
{
return apcu_store($this->statusKeyLastAppliedEventId, $eid);
}
}
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