Re: ??: postgres cpu 100% need help

On Tue, Oct 27, 2015 at 12:14 PM, Bill Moran <wmoran(at)potentialtech(dot)com> wrote:
> On Tue, 27 Oct 2015 11:30:45 +0800
> "657985552(at)qq(dot)com" <657985552(at)qq(dot)com> wrote:
>
>> Dear sir:
>> Recently a wired question about postgresql database really bothered me a lot, so i really need your help. Here is the problem, in the most situations the postgre database work very well, Average 3500tps/s per day, the cpu usage of its process is 3%~10% and every query can be responsed in less than 20ms, but sometimes the cpu usages of its process can suddenly grow up to 90%+ , at that time a simple query can cost 2000+ms. ps: My postgresql version is 9.3.5 and the database is oltp server.
>
> 9.3.5 is pretty old, you should probably schedule an upgrade.
>
>> shared_buffers | 25GB
>
> Try setting this to 16GB. It's been a while since I tested on
> large-memory/high-load systems, but I seem to remember that
> shared_buffers above 16G could cause these sorts of intermittant
> stalls.
>
> If that doesn't improve the situation, you'll probably need to
> provide more details, specifically the layout of the table in
> question, as well as the queries that are active when the
> problem occurs, and the contents of the pg_locks table when
> the problem is occurring.

possible culprits:
*) io based problems (check iowait, rule this out first)
*) THP compaction (rule this out second)
*) runaway query plan
*) concurrency problems within postgres itself (perf top capture
during load is essential)

maybe some other things I'm not thinking of.

merlin