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查看 Percona XtraDB Cluster 在 IST 時的進度

Percona 的「Tracking IST Progress in Percona XtraDB Cluster」這篇介紹了 PXC 在 IST 時的進度。

是個新功能,很簡單的可以看到目前進度,也可以拿來當作 health check 的一部分,避免開機剛起來時開始提供服務:

mysql> show status like 'wsrep_ist_receive_status';
+--------------------------+--------------------------------------------------------+
| Variable_name | Value |
+--------------------------+--------------------------------------------------------+
| wsrep_ist_receive_status | 3% complete, received seqno 1421771 of 1415410-1589676 |
+--------------------------+--------------------------------------------------------+
1 row in set (0.00 sec)
....
mysql> show status like 'wsrep_ist_receive_status';
+--------------------------+---------------------------------------------------------+
| Variable_name | Value |
+--------------------------+---------------------------------------------------------+
| wsrep_ist_receive_status | 52% complete, received seqno 1506799 of 1415410-1589676 |
+--------------------------+---------------------------------------------------------+
1 row in set (0.00 sec)
....
mysql> show status like 'wsrep_ist_receive_status';
+--------------------------+---------------------------------------------------------+
| Variable_name | Value |
+--------------------------+---------------------------------------------------------+
| wsrep_ist_receive_status | 97% complete, received seqno 1585923 of 1415410-1589676 |
+--------------------------+---------------------------------------------------------+
1 row in set (0.00 sec)
mysql> show status like 'wsrep_ist_receive_status';
+--------------------------+-------+
| Variable_name | Value |
+--------------------------+-------+
| wsrep_ist_receive_status | |
+--------------------------+-------+
1 row in set (0.00 sec)

Galera Cluster 不必要的 SST 行為的改善

Percona 的人解釋了 Galera Cluster 為什麼在某些情況下會需要 SST (整份重傳) 而不是 IST (傳最後造成差異的部分),以及開發商在 3.19 版對應的改進:「Galera Cache (gcache) is finally recoverable on restart」。

原因在於 IST 所需要的記錄會在重開機時消失,所以當其他節點加入時沒辦法給,只好給 SST:

The DONOR node caches missing write-sets in Galera cache, but on restart this cache is wiped clean and restarted fresh. So the DONOR node doesn’t have a Galera cache to donate missing write-sets.

gcache.recover 這個參數打開後就會啟用記錄,另外也可以挑著開就好:

The user can set this option for all nodes, or selective nodes, based on disk usage.

另外最重要的是,之後的版本才會有,所以得繼續等...:

And yes, Percona XtraDB Cluster inherits this feature in its upcoming release.

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