"wsrep in pre-commit stage" sometimes slows down my queries

[Arkadiy Arkadiy]

This isn't a general problem. Happens only few times per day.

However, I haven't found any documentation regarding the "wsrep in pre-commit stage" status for queries and what could be causing it to take longer than normal.

Sometimes, my UPDATE/INSERT queries take around 3-20 seconds to complete. 

I setup profiling to see what is actually happening and here is what it showed:

UPDATE users SET user_lastlogin=NOW() WHERE user_id='103396'

Status	Duration
starting	0.000020
checking permissions	0.000003
Opening tables	0.000010
init	0.000032
System lock	0.000037
updating	0.000189
end	0.000003
Waiting for query cache lock	0.000002
end	0.000051
query end	0.000007
wsrep in pre-commit stage	10.479955
ha_commit_one_phase(287176997)	0.000004
innobase_commit_low():trx_comm	0.000016
ha_commit_one_phase(287176997)	0.000052
wsrep in pre-commit stage	0.000017
closing tables	0.000011
freeing items	0.000034
logging slow query	0.000002
logging slow query	0.000002
cleaning up	0.000002

I would love to know what actually the "pre-commit" stage does and how it is tuned/monitored.

I have attached my "show status" and "show variables" in case someone can take a deeper look.

Once again, this isn't a general problem and happens only a few times per day.

Thank you!