Re: Running lots of inserts from selects on 9.4.5

> On Feb 11, 2016, at 4:41 PM, Dan Langille <dan(at)langille(dot)org> wrote:
>
>> On Feb 10, 2016, at 5:13 AM, Dan Langille <dan(at)langille(dot)org> wrote:
>>
>>> On Feb 10, 2016, at 2:47 AM, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
>>>
>>> On Tue, Feb 9, 2016 at 4:09 PM, Dan Langille <dan(at)langille(dot)org> wrote:
>>>> I have a wee database server which regularly tries to insert 1.5 million or
>>>> even 15 million new rows into a 400 million row table. Sometimes these
>>>> inserts take hours.
>>>>
>>>> The actual query to produces the join is fast. It's the insert which is
>>>> slow.
>>>>
>>>> INSERT INTO File (FileIndex, JobId, PathId, FilenameId, LStat, MD5,
>>>> DeltaSeq)
>>>> SELECT batch_testing.FileIndex, batch_testing.JobId, Path.PathId,
>>>> Filename.FilenameId, batch_testing.LStat, batch_testing.MD5,
>>>> batch_testing.DeltaSeq
>>>> FROM batch_testing JOIN Path ON (batch_testing.Path = Path.Path)
>>>> JOIN Filename ON (batch_testing.Name =
>>>> Filename.Name);
>>>>
>>>> This is part of the plan: http://img.ly/images/9374145/full created via
>>>> http://tatiyants.com/pev/#/plans
>>>>
>>>> This gist contains postgresql.conf, zfs settings, slog, disk partitions.
>>>>
>>>> https://gist.github.com/dlangille/33331a8c8cc62fa13b9f
>>>
>>> The table you are inserting into has 7 indexes, all of which have to
>>> be maintained. The index on the sequence column should be efficient
>>> to maintain. But for the rest, if the inserted rows are not naturally
>>> ordered by any of the indexed columns then it would end up reading 6
>>> random scattered leaf pages in order to insert row pointers. If none
>>> those pages are in memory, that is going to be slow to read off from
>>> hdd in single-file. Also, you are going dirty all of those scattered
>>> pages, and they will be slow to write back to hdd because there
>>> probably won't be much opportunity for write-combining.
>>>
>>> Do you really need all of those indexes?
>>>
>>> Won't the index on (jobid, pathid, filenameid) service any query that
>>> (jobid) does, so you can get rid of the latter?
>>>
>>> And unless you have range queries on fileindex, like "where jobid = 12
>>> and fileindex between 4 and 24" then you should be able to replace
>>> (jobid, fileindex) with (fileindex,jobid) and then get rid of the
>>> stand-alone index on (fileindex).
>>>
>>> If you add an "order by" to the select statement which order by the
>>> fields of one of the remaining indexes, than you could make the
>>> maintenance of that index become much cheaper.
>>
>> I will make these changes one-by-one and test each. This will be interesting.
>
> On a test server, the original insert takes about 45 minutes. I removed all indexes. 25 minutes.
>
> Thank you.

Today I tackled the production server. After discussion on the Bacula devel mailing list (http://marc.info/?l=bacula-devel&m=145537742804482&w=2 <http://marc.info/?l=bacula-devel&m=145537742804482&w=2>)
I compared my schema to the stock schema provided with Bacula. Yes, I found
extra indexes. I saved the existing schema and proceeded to remove the indexes
from prod not found in the default.

The query time went from 223 minute to 4.5 minutes. That is 50 times faster.

I think I can live with that. :)

Jeff: if you show up at PGCon, dinner is on me. Thank you.

--
Dan Langille - BSDCan / PGCon
dan(at)langille(dot)org