protected function getShardConnection($shardID, array $options = [])
{
if (!is_numeric($shardID)) {
throw new Exception('$shardID must be an integer');
}
$isWriteQuery = !empty($options['isWriteQuery']);
$lastLinkFailed = !empty($options['lastLinkFailed']);
$writeInReadMode = !empty($options['writeInReadMode']);
// TEMP
if (get_called_class() == 'Zotero_FullText_DB') {
$linkID = "FT" . $shardID;
} else {
$linkID = $shardID;
}
if ($this->isReadOnly($shardID) && $isWriteQuery && !$writeInReadMode) {
throw new Exception("Cannot get link for writing to shard {$shardID} in read-only mode");
}
// Master queries always use the cached link that was created at class construction
if ($shardID == 0) {
//error_log($this->connections[$linkID]->link->getConnection()->host_info);
return $this->connections[$linkID];
}
// For read-only mode and read queries, use a cached link if available. Since this is
// done before checking the latest shard info, it's possible for subsequent read queries
// in a request to go through even if the shard was since disabled, but that's generally
// not a big deal, and new requests will check the shard info again and throw.
//
// Read-only mode
if ($this->isReadOnly($shardID) && !$writeInReadMode) {
// Use a cached replica link if available.
if (isset($this->replicaConnections[$linkID])) {
// If the last link failed, try the next one. If no more, that's fatal.
if ($lastLinkFailed) {
$lastHost = $this->replicaConnections[$linkID][0]->host;
if (sizeOf($this->replicaConnections[$linkID]) == 1) {
throw new Exception("Read failed from replica {$lastHost} -- no more replica connections", Z_ERROR_SHARD_UNAVAILABLE);
}
error_log("WARNING: Read failed from replica {$lastHost} -- retrying on another replica");
array_shift($this->replicaConnections[$linkID]);
}
//error_log($this->replicaConnections[$linkID][0]->link->getConnection()->host_info);
return $this->replicaConnections[$linkID][0];
}
} else {
if (!$isWriteQuery && isset($this->connections[$linkID])) {
//error_log($this->connections[$linkID]->link->getConnection()->host_info);
return $this->connections[$linkID];
}
}
$shardInfo = Zotero_Shards::getShardInfo($shardID);
if (!$shardInfo) {
throw new Exception("Invalid shard {$shardID}");
}
if ($shardInfo['state'] == 'down') {
throw new Exception("Shard {$shardID} is down", Z_ERROR_SHARD_UNAVAILABLE);
} else {
if ($shardInfo['state'] == 'readonly') {
if ($isWriteQuery && get_called_class() != 'Zotero_Admin_DB') {
throw new Exception("Cannot write to read-only shard {$shardID}", Z_ERROR_SHARD_READ_ONLY);
}
}
}
if ($this->isReadOnly($shardID) && !$writeInReadMode) {
$replicas = Zotero_Shards::getReplicaInfo($shardInfo['shardHostID']);
if ($replicas) {
$writerCacheKey = 'shardHostReplicasWriter_' . $shardInfo['shardHostID'];
$writerAddress = Z_Core::$MC->get($writerCacheKey);
$writerConn = null;
// Randomize replica order
shuffle($replicas);
foreach ($replicas as $replica) {
$info = $shardInfo;
$info['address'] = $replica['address'];
$info['port'] = $replica['port'];
$conn = new Zotero_DB_Connection();
$conn->host = $info['address'];
$conn->shardID = $linkID;
$conn->link = $this->getLinkFromConnectionInfo($info);
if ($replica['address'] == $writerAddress) {
$writerConn = $conn;
} else {
$this->replicaConnections[$linkID][] = $conn;
}
}
// If we know the writer, add it last, so that all read replicas are tried first
if ($writerConn) {
$this->replicaConnections[$linkID][] = $writerConn;
} else {
try {
$results = $this->replicaConnections[$linkID][0]->link->query("SHOW GLOBAL VARIABLES LIKE 'innodb_read_only'");
$row = $results->fetch(Zend_Db::FETCH_ASSOC);
$connReadOnly = $row ? $row['Value'] : false;
// If we found the writer
if ($connReadOnly == "OFF") {
// Store host in memcached so that every request doesn't need to check
// the variables to sort the writer last.
//
// This can probably be increased, because the only consequence of not
// knowing the writer is that a few requests could use the writer
// for reads.
Z_Core::$MC->set($writerCacheKey, $this->replicaConnections[$linkID][0]->host, 60);
// If more than one connection, move writer connection to end and
// close it
if (sizeOf($this->replicaConnections[$linkID]) > 1) {
$conn = array_shift($this->replicaConnections[$linkID]);
$this->replicaConnections[$linkID][] = $conn;
$conn->link->closeConnection();
}
}
} catch (Exception $e) {
error_log("WARNING: Failed checking replica state: {$e}");
}
}
//error_log($this->replicaConnections[$linkID][0]->link->getConnection()->host_info);
return $this->replicaConnections[$linkID][0];
}
}
// Host isn't read-only or down, so write queries can use a cached link if available.
// Otherwise, make a new link.
if (!isset($this->connections[$linkID])) {
$conn = new Zotero_DB_Connection();
$conn->host = $shardInfo['address'];
$conn->shardID = $linkID;
$conn->link = $this->getLinkFromConnectionInfo($shardInfo);
$this->connections[$linkID] = $conn;
}
//error_log($this->connections[$linkID]->link->getConnection()->host_info);
return $this->connections[$linkID];
}
