Troubleshooting
Problem
plogpl,plogcur or plothr mutex can be observered in in the output of 'onstat -g lmx' which would indicate a certain bottleneck and lead to transactions blocked for short moments.
Symptom
For example onstat -g lmx shows:
IBM Informix Dynamic Server Version 11.50.FC8 -- On-Line -- Up 16 days 12:21:27 -- 40645184 Kbytes
Locked mutexes:
mid addr name holder lkcnt waiter waittime
......
21551 7000000135f3f38 plogpl 83 0 12786792 1
12786751 1
12786746 1
12786757 1
12786730 1
12786697 1
12786704 1
12786750 1
..........
21552 7000000135f3fb0 plogcur 12786698 0 83 1
21553 7000000135f40b0 plothr 83 0
So all three kinds of mutex seen as locked here, one even (plogpl) with a significant waiters list. You might as well see only one or two of them locked.
If these mutexes show frequently in 'onstat -g lmx' or 'onstat -g wmx', this would indicate a bottleneck and might be a reason for limitted performance.
Using 'onstat -g stk <thread_id>', you might be able to catch such thread's (holder or waiter) stack while performing physical log related activity. Quite typically you'd see the following at the top of such stack:
yield_processor_mvp
mt_lock_wait
mt_lock
(bfphysflush)
bfphyslogx
...
denoting either physical log disk i/o (phys. log buffer flushing) or just physical logging.
Cause
Reasons might be among the following:
- small physical log buffer (unless unbuffered logging is used in which case a larger buffer possibly wouldn't be utilized)
- physical log residing on slow disk, or physical log disk i/o slow for some reason
- very aggressive (low) LRU_MAX_DIRTY setting, causing frequent phys. log buffer flushing
Diagnosing The Problem
Use 'onstat -g iof' (or 'onstag -g ioh' if available) to gauge disk i/o speed.
Resolving The Problem
Adjust PHYSBUFF and/or BUFFERPOOL (max_dirty, min_dirty) setting accoring to your findings.
Related Information
[{"Product":{"code":"SSGU8G","label":"Informix Servers"},"Business Unit":{"code":"BU053","label":"Cloud & Data Platform"},"Component":"--","Platform":[{"code":"PF002","label":"AIX"},{"code":"PF010","label":"HP-UX"},{"code":"PF027","label":"Solaris"}],"Version":"11.5;11.7;12.1","Edition":"","Line of Business":{"code":"","label":""}}]
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Document Information
Modified date:
16 June 2018
UID
swg21653615