Galera Functions¶
Starting with version 4 of Galera Cluster, there are several Galera functions available. At this point, the Galera functions related to Global Transaction ID (GTID). They return a GTID or have effect on transactions related to a GTID.
| Function | Arguments | Initial Version |
|---|---|---|
| WSREP_LAST_SEEN_GTID() | 4.0 | |
| WSREP_LAST_WRITTEN_GTID() | 4.0 | |
| WSREP_SYNC_WAIT_UPTO_GTID() | gtid [timeout] |
4.0 |
WSREP_LAST_SEEN_GTID()
Much like LAST_INSERT_ID() for getting the identification number of the last row inserted in MySQL, this function returns the Global Transaction ID of the last write transaction observed by the client.
| Function | WSREP_LAST_SEEN_GTID() |
| Arguments | None |
| Initial Version | Version 4.0 |
This function returns the Global Transaction ID of the last write transaction observed by the client. It can be useful in combination with WSREP_SYNC_WAIT_UPTO_GTID(). You can use this parameter to identify the transaction upon which it should wait before unblocking the client.
Below is an example of how you might use the WSREP_LAST_SEEN_GTID() function to get the Global Transaction ID of the last write transaction observed:
SELECT WSREP_LAST_SEEN_GTID();
WSREP_LAST_WRITTEN_GTID()
This function returns the Global Transaction ID of the last write transaction made by the client.
| Function | WSREP_LAST_WRITTEN_GTID() |
| Arguments | None |
| Initial Version | Version 4.0 |
This function returns the Global Transaction ID of the last write transaction made by the client. This can be useful in combination with WSREP_SYNC_WAIT_UPTO_GTID(). You can use this parameter to identify the transaction upon which it should wait before unblocking the client.
Below is an example of how you might use the WSREP_LAST_SEEN_GTID() function to get the Global Transaction ID of the last write transaction observed:
BEGIN;
UPDATE table_name SET id = 0
WHERE field = 'example';
COMMIT;
SELECT WSREP_LAST_WRITTEN_GTID();
WSREP_SYNC_WAIT_UPTO_GTID()
This function blocks the client until the node applies and commits the given transaction.
| Function | WSREP_SYNC_WAIT_UPTO_GTID() |
| Required Arguments | Global Transaction ID |
| Optional Arguments | timeout |
| Initial Version | Version 4.0 |
This function blocks the client until the node applies and commits the given Global Transaction ID. Optional argument accepts timeout in seconds. If you don’t provide a timeout, it will continue to block indefinitely. It returns the following values:
1: The node applied and committed the given Global Transaction ID.ER_LOCAL_WAIT_TIMEOUTError: The function times out before the node can apply the transaction.ER_WRONG_ARGUMENTSError: The function is given an incorrect Global Transaction ID.
Below is an example of how you might use the WSREP_SYNC_WAIT_UPTO_GTID() function:
$transaction_gtid = SELECT WSREP_LAST_SEEN_GTID();
...
SELECT WSREP_SYNC_WAIT_UPTO_GTID($transaction_gtid);
