5.6 cluster reports wsrep_cert_deps_distance=1.0 in all cases | Parallel Apply not working

Bug #1277703 reported by Jay Janssen on 2014-02-07
12
This bug affects 2 people
Affects Status Importance Assigned to Milestone
MySQL patches by Codership
Status tracked in 5.6
5.5
High
Teemu Ollakka
5.6
High
Teemu Ollakka
Percona XtraDB Cluster moved to https://jira.percona.com/projects/PXC
Status tracked in 5.6
5.5
Fix Released
High
Unassigned
5.6
Fix Released
High
Unassigned

Bug Description

PXC 5.6.16, Galera 3.3, latest GA release.

Standard Linux 3 node running sysbench 8 threads on one node. Other nodes permanently report wsrep_cert_deps_distance=1.

| wsrep_cert_deps_distance | 1.000000 |
| wsrep_apply_oooe | 0.000000 |
| wsrep_apply_oool | 0.000000 |
| wsrep_apply_window | 1.101769 |
| wsrep_commit_oooe | 0.000000 |
| wsrep_commit_oool | 0.000000 |
| wsrep_commit_window | 1.000000 |

Does this mean parallel apply is not working or wsrep_cert_deps_distance is simply broken?

summary: - 5.6 cluster node that is a slave with parallel worker threads seems to
- generate writesets that are not parallelizable
+ 5.6 cluster reports wsrep_cert_deps_distance=1.0 in all cases
description: updated

I can confirm that on PXC 5.5 wsrep_cert_deps_distance reports properly with the same sysbench workload:

ip-10-235-58-55 mysql> show global status like 'wsrep_cert%';
+--------------------------+------------+
| Variable_name | Value |
+--------------------------+------------+
| wsrep_cert_deps_distance | 440.819692 |
| wsrep_cert_index_size | 842 |
+--------------------------+------------+
2 rows in set (0.00 sec)

However, on PXC 5.6, whether Galera 2 or Galera 3, I only get a value of '1' for wsrep_cert_deps_distance.

| wsrep_cert_deps_distance | 1.000000 |

Teemu Ollakka (teemu-ollakka) wrote :

It looks that each THD entering to pre-commit stage has thd->wsrep_PA_safe set to false, done in Query_log_event constructor when adding BEGIN Query_log_event into IO cache. This in turn disables PA for transactions, seen as wsrep_cert_deps_distance 1.000000 in wsrep status.

Teemu Ollakka (teemu-ollakka) wrote :

Fixes pushed:

5.5: http://bazaar.launchpad.net/~codership/codership-mysql/wsrep-5.5/revision/3947
5.6: http://bazaar.launchpad.net/~codership/codership-mysql/5.6/revision/4038

Pushed fix to 5.5 too to avoid disabling PA in case of SAVEPOINT or ROLLBACK TO SAVEPOINT.

summary: - 5.6 cluster reports wsrep_cert_deps_distance=1.0 in all cases
+ 5.6 cluster reports wsrep_cert_deps_distance=1.0 in all cases | Parallel
+ Apply not working

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PXC-994

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