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From Stepan Migunov <Stepan.Migu...@firstlinesoftware.com>
Subject RE: Performance degradation on query analysis
Date Fri, 27 Sep 2019 08:04:09 GMT
Thanks Josh,  you are right, we have actually disabled automatic major
compaction. Now we added SYSTEM.STATS to weekly compaction and I hope this
resolve the issue.


-----Original Message-----
From: Josh Elser [mailto:elserj@apache.org]
Sent: Tuesday, September 24, 2019 6:39 PM
To: user@phoenix.apache.org
Subject: Re: Performance degradation on query analysis

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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