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From Josh Elser <els...@apache.org>
Subject Re: Performance degradation on query analysis
Date Tue, 24 Sep 2019 15:38:35 GMT
Did you change your configuration to prevent compactions from regularly 
happening, Stepan?

By default, you should have a major compaction run weekly which would 
have fixed this for you, although minor compactions would have run 
automatically as well to rewrite small hfiles as you are creating new 
one (generating new stats).

On 9/19/19 4:50 PM, Ankit Singhal wrote:
> Please schedule compaction on SYSTEM.STATS table to clear the old entries.
> 
> On Thu, Sep 19, 2019 at 1:48 PM Stepan Migunov 
> <Stepan.Migunov@firstlinesoftware.com 
> <mailto:Stepan.Migunov@firstlinesoftware.com>> wrote:
> 
>     Thanks, Josh. The problem was really related to reading the SYSTEM.STATS
>     table.
>     There were only 8,000 rows in the table, but COUNT took more than 10
>     minutes. I noticed that the storage files (34) had a total size of
>     10 GB.
> 
>     DELETE FROM SYSTEM.STATS did not help - the storage files are still
>     10 GB,
>     and COUNT took a long time.
>     Then I truncated the table from the hbase shell. And this fixed the
>     problem - after UPDATE STATS for each table, everything works fine.
> 
>     Are there any known issues with SYSTEM.STATS table? Apache Phoenix
>     4.13.1
>     with 15 Region Servers.
> 
>     -----Original Message-----
>     From: Josh Elser [mailto:elserj@apache.org <mailto:elserj@apache.org>]
>     Sent: Tuesday, September 17, 2019 5:16 PM
>     To: user@phoenix.apache.org <mailto:user@phoenix.apache.org>
>     Subject: Re: Performance degradation on query analysis
> 
>     Can you share the output you see from the EXPLAIN? Does it differ
>     between
>     times it's "fast" and times it's "slow"?
> 
>     Sharing the table(s) DDL statements would also help, along with the
>     shape
>     and version of your cluster (e.g. Apache Phoenix 4.14.2 with 8
>     RegionServers).
> 
>     Spit-balling ideas:
> 
>     Could be reads over the SYSTEM.CATALOG table or the SYSTEM.STATS table.
> 
>     Have you looked more coarsely at the RegionServer logs/metrics? Any
>     obvious
>     saturation issues (e.g. handlers consumed, JVM GC pauses, host CPU
>     saturation)?
> 
>     Turn on DEBUG log4j client side (beware of chatty ZK logging) and see if
>     there's something obvious from when the EXPLAIN is slow.
> 
>     On 9/17/19 3:58 AM, Stepan Migunov wrote:
>      > Hi
>      > We have an issue with our production environment - from time to
>     time we
>      > notice a significant performance degradation for some queries.
>     The strange
>      > thing is that the EXPLAIN operator for these queries takes the
>     same time
>      > as queries execution (5 minutes or more). So, I guess, the issue is
>      > related to query's analysis but not data extraction. Is it
>     possible that
>      > issue is related to SYSTEM.STATS access problem? Any other ideas?
>      >
> 

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