No new bugs reported

Introduced automatic retry loop for transient errors and corresponding statistic to count the number of implicit retries. Some distributed database clusters use transient errors to hint a client to retry its operation in a bit. Most often, the client is then supposed to halt execution (sleep) for a short moment before retrying the desired operation. Immediately failing over to another node is not necessary in response to the error. Instead, a retry loop can be performed. Common situation when using MySQL Cluster.

Fixed #60605 PHP segmentation fault when mysqlnd_ms is enabled.

Setting transaction stickiness disables all load balancing, including automatic failover, for the duration of a transaction. So far connection switches could have happened in the middle of a transaction in multi-master configurations and during automatic failover although transaction monitoring had detected transaction boundaries properly.

BC break and bug fix. SQL hints enforcing the use of a specific kind of server ( MYSQLND_MS_MASTER_SWITCH , MYSQLND_MS_SLAVE_SWITCH , MYSQLND_MS_LAST_USED_SWITCH ) are ignored for the duration of a transaction of transaction stickiness is enabled and transaction boundaries have been detected properly.

This is a change in behaviour. However, it is also a bug fix and a step to align behaviour. If, in previous versions, transaction stickiness, one of the above listed SQL hints and the quality of service filtering was combined it could happened that the SQL hints got ignored. In some case the SQL hints did work, in other cases they did not. The new behaviour is more consistent. SQL hints will always be ignore for the duration of a transaction, if transaction stickiness is enabled.

Please note, transaction boundary detection continues to be based on API call monitoring. SQL commands controlling transactions are not monitored.

BC break and bug fix. Calls to mysqlnd_ms_set_qos will fail when done in the middle of a transaction if transaction stickiness is enabled. Connection switches are not allowed for the duration of a transaction. Changing the quality of service likely results on a different set of servers qualifying for query execution, possibly making it necessary to switch connections. Thus, the call is not allowed in during an active transaction. The quality of server can, however, be changed in between transactions.

Introduced the node_group filter. The filter lets you organize servers (master and slaves) into groups. Queries can be directed to a certain group of servers by prefixing the query statement with a SQL hint/comment that contains the groups configured name. Grouping can be used for partitioning and sharding, and also to optimize for local caching. In the case of sharding, a group name can be thought of like a shard key. All queries for a given shard key will be executed on the configured shard. Note: both the client and server must support sharding for sharding to function with mysqlnd_ms.

Extended configuration file validation during PHP startup (RINIT). An E_WARNING level error will be thrown if the configuration file can not be read (permissions), is empty, or the file (JSON) could not be parsed. Warnings may appear in log files, which depending on how PHP is configured.

Distributions that aim to provide a pre-configured setup, including a configuration file stub, are asked to put {} into the configuration file to prevent this warning about an invalid configuration file.

Further configuration file validation is done when parsing sections upon opening a connection. Please, note that there may still be situations when an invalid plugin configuration file does not lead to proper error messages but a failure to connect.

As of PHP 5.5.0, improved support for transaction boundaries detection was added for mysqli. The mysqli extension has been modified to use the new C API calls of the mysqlnd library to begin, commit, and rollback a transaction or savepoint. If trx_stickiness is used to enable transaction aware load balancing, the mysqli_begin, mysqli_commit and mysqli_rollback functions will now be monitered by the plugin, to go along with the mysqli_autocommit function that was already supported. All SQL features to control transactions are also available through the improved mysqli transaction control related functions. This means that it is not required to issue SQL statements instead of using API calls. Applications using the appropriate API calls can be load balanced by PECL/mysqlnd_ms in a completely transaction-aware way.

Please note, PDO_MySQL has not been updated yet to utilize the new mysqlnd API calls. Thus, transaction boundary detection with PDO_MySQL continues to be limited to the monitoring by passing in PDO::ATTR_AUTOCOMMIT to PDO::setAttribute.

Introduced trx_stickiness=on. This trx_stickiness option differs from trx_stickiness=master as it tries to execute a read-only transaction on a slave, if quality of service (consistency level) allows the use of a slave. Read-only transactions were introduced in MySQL 5.6, and they offer performance gains.

Query cache support is considered beta if used with the mysqli API. It should work fine with primary copy based clusters. For all other APIs, this feature continues to be called experimental.

The code examples in the mysqlnd_ms source were updated.

Fixed build with PHP 5.5

BC break: Renamed plugin configuration setting ini_file to config_file. In early versions the plugin configuration file used ini style. Back then the configuration setting was named accordingly. It has now been renamed to reflect the newer file format and to distinguish it from PHP's own ini file (configuration directives file).

Introduced new default charset setting server_charset to allow proper escaping before a connection is opened. This is most useful when using lazy connections, which are a default.

Introduced wait_for_gtid_timeout setting to throttle slave reads that need session consistency. If global transaction identifier are used and the service level is set to session consistency, the plugin tries to find up-to-date slaves. The slave status check is done by a SQL statement. If nothing else is set, the slave status is checked only one can the search for more up-to-date slaves continues immediately thereafter. Setting wait_for_gtid_timeout instructs the plugin to poll a slaves status for wait_for_gtid_timeout seconds if the first execution of the SQL statement has shown that the slave is not up-to-date yet. The poll will be done once per second. This way, the plugin will wait for slaves to catch up and throttle the client.

New failover strategy loop_before_master. By default the plugin does no failover. It is possible to enable automatic failover if a connection attempt fails. Upto version 1.3 only master strategy existed to failover to a master if a slave connection fails. loop_before_master is similar but tries all other slaves before attempting to connect to the master if a slave connection fails.

The number of attempts can be limited using the max_retries option. Failed hosts can be remembered and skipped in load balancing for the rest of the web request. max_retries and remember_failed are considered experimental although decent stability is given. Syntax and semantics may change in the future without prior notice.

Fixed problem with multi-master where although in a transaction the queries to the master weren't sticky and were spread all over the masters (RR). Still not sticky for Random. Random_once is not affected.

Fixed problem with building together with QC.

Added cache option to quality-of-service (QoS) filter.

Support for built-in global transaction identifier feature of MySQL 5.6.5-m8 or newer.

Introduced quality-of-service (QoS) filter. Service levels provided by QoS filter:

Added the mysqlnd_ms_set_qos function to set the required connection quality at runtime. The new constants related to mysqlnd_ms_set_qos are:

Added client-side global transaction id injection (GTID).

New statistics related to GTID:

Added mysqlnd_ms_get_last_gtid to fetch the last global transaction id.

Enabled support for multi master without slaves.

Added the (chainable) filter concept:

New statistics: use_master_guess, use_slave_guess.