Re: [GENERAL] low perfomances migrating from 9.3 to 9.5

[thomas veymont]

hi Melvin, Adrian,

>
> Where did you get the respective versions of Postgres?
>

both were compiled from source, from the official website tar files.
gcc is 4.1.2 20080704 (Red Hat 4.1.2-48)

>
> Where they installed the same way?
>

yes, exactly the same.  My configure command line is:
./configure --prefix=/usr/local/pgsqlX.XX --with-perl --with-python
--with-tcl --with-openssl --with-pam --with-ldap --with-libxml
--with-libxslt --with-system-tzdata=/usr/share/zoneinfo/>

>
> You mentioned the log feed showing obvious performance issues, can we see
the relevant portions?
>

I was meaning the log feed is obviously "slow" because you can almost
"read" the log lines going through. You usually can't because it's too fast.




*>> I have to ask, > was a vacuumdb -Z  OR psql -U postgres -c ANALYZE ; *



*> done after the migration?>> Without accurate stats, performance goes
down the drain*

*>*
You're right. I did not run ANALYZE in the first time (assuming autovacuum
would do it when needed). But it should be noted that :
- even re-injecting the 9.3 dumps into the fresh 9.5 engine was much longer
than expected (it is agreed that I cannot run ANALYZE before re-injecting
the dumps ;)
- the pgbench run on both 9.3/9.5 systems were run without ANALYZE. And
yet, the 9.3 test provided better results than 9.5.

To be clear in my mind about it, I think I need to re-run these tests and
check whether it's machine/OS dependant or even I am doing my test the
wrong way.
I will be back to you with more objective values by next week.

thanks for helping,
Tom


2016-07-27 17:14 GMT+02:00 Melvin Davidson <melvin6...@gmail.com>:

>
>
> On Wed, Jul 27, 2016 at 11:01 AM, Adrian Klaver <adrian.kla...@aklaver.com
> > wrote:
>
>> On 07/27/2016 07:52 AM, thomas veymont wrote:
>>
>>>
>>> 2016-07-27 14:11 GMT+02:00 Michael Paquier <michael.paqu...@gmail.com
>>> <mailto:michael.paqu...@gmail.com>>:
>>>
>>>
>>>
>>>
>>> And do you see changes if you increase min_wal_size? This will
>>> increase the number of WAL segments recycled instead of removed at
>>> each checkpoint.
>>> --
>>> Michael
>>>
>>>
>>> I have seen no improvment with the following parameters in 9.5:
>>> max_wal_size = 3GB
>>> min_wal_size = 512MB
>>> #checkpoint_completion_target = 0.5 # checkpoint target duration,
>>> 0.0 - 1.0
>>> #checkpoint_warning = 30s   # 0 disables
>>>
>>> while my 9.3 configuration is:
>>> checkpoint_segments = 128   # in logfile segments, min 1,
>>> 16MB each
>>> #checkpoint_timeout = 5min  # range 30s-1h
>>> checkpoint_completion_target = 0.9  # checkpoint target duration,
>>> 0.0 - 1.0
>>> #checkpoint_warning = 30s   # 0 disables
>>>
>>> I have just run a quick pgbench test to get some objective numbers.
>>> Both tests were run on the same machine (ie. production machine), same
>>> disk, same logical volume :
>>>
>>> On 9.5 :
>>>
>>> $ pgbench -c 4 -j 2 -T 600 test
>>> starting vacuum...end.
>>> transaction type: TPC-B (sort of)
>>> scaling factor: 70
>>> query mode: simple
>>> number of clients: 4
>>> number of threads: 2
>>> duration: 600 s
>>> number of transactions actually processed: 77318
>>> latency average: 31.041 ms
>>> tps = 128.859708 (including connections establishing)
>>> tps = 128.860447 (excluding connections establishing)
>>>
>>> On 9.3 :
>>>
>>> $ pgbench -c 4 -j 2 -T 600 test
>>> starting vacuum...end.
>>> transaction type: TPC-B (sort of)
>>> scaling factor: 70
>>> query mode: simple
>>> number of clients: 4
>>> number of threads: 2
>>> duration: 600 s
>>> number of transactions actually processed: 1834436
>>> latency average: 1.308 ms
>>> tps = 3057.387254 (including connections establishing)
>>> tps = 3057.398493 (excluding connections establishing)
>>>
>>> Note that the 9.3 is handling others production requests in the same
>>> time.
>>>
>>> Is a checkpoint_segment/WAL problem still to be suspected ?
>>>
>>
>> Where did you get the respective versions of Postgres?
>>
>> Where they installed the same way?
>>
>> You mentioned the log feed showing obvious performance issues, can we see
>> the relevant portions?
>>
>>
>>> cheers
>>> Tom
>>>
>>>
>>
>> --
>> Adrian Klaver
>> adrian.kla...@aklaver.com
>>
>>
>> --
>> Sent via pgsql-general mailing list (pgsql-general@postgresql.org)
>> To make changes to your subscription:
>> http://www.postgresql.org/mailpref/pgsql-general
>>
>
>
>
>
> *I have to ask, was a vacuumdb -Z  OR psql -U postgres -c ANALYZE ; *
>
>
> *done after the migration?*
>
> *Without accurate stats, performance goes down the drain.*
> --
> *Melvin Davidson*
> I reserve the right to fantasize.  Whether or not you
> wish to share my fantasy is entirely up to you.
>

Re: [GENERAL] low perfomances migrating from 9.3 to 9.5

[thomas veymont]

2016-07-27 14:11 GMT+02:00 Michael Paquier :

>
>
> And do you see changes if you increase min_wal_size? This will
> increase the number of WAL segments recycled instead of removed at
> each checkpoint.
> --
> Michael
>

I have seen no improvment with the following parameters in 9.5:
max_wal_size = 3GB
min_wal_size = 512MB
#checkpoint_completion_target = 0.5 # checkpoint target duration, 0.0 -
1.0
#checkpoint_warning = 30s   # 0 disables

while my 9.3 configuration is:
checkpoint_segments = 128   # in logfile segments, min 1, 16MB
each
#checkpoint_timeout = 5min  # range 30s-1h
checkpoint_completion_target = 0.9  # checkpoint target duration, 0.0 -
1.0
#checkpoint_warning = 30s   # 0 disables

I have just run a quick pgbench test to get some objective numbers.
Both tests were run on the same machine (ie. production machine), same
disk, same logical volume :

On 9.5 :

$ pgbench -c 4 -j 2 -T 600 test
starting vacuum...end.
transaction type: TPC-B (sort of)
scaling factor: 70
query mode: simple
number of clients: 4
number of threads: 2
duration: 600 s
number of transactions actually processed: 77318
latency average: 31.041 ms
tps = 128.859708 (including connections establishing)
tps = 128.860447 (excluding connections establishing)

On 9.3 :

$ pgbench -c 4 -j 2 -T 600 test
starting vacuum...end.
transaction type: TPC-B (sort of)
scaling factor: 70
query mode: simple
number of clients: 4
number of threads: 2
duration: 600 s
number of transactions actually processed: 1834436
latency average: 1.308 ms
tps = 3057.387254 (including connections establishing)
tps = 3057.398493 (excluding connections establishing)

Note that the 9.3 is handling others production requests in the same time.

Is a checkpoint_segment/WAL problem still to be suspected ?

cheers
Tom

Re: [GENERAL] low perfomances migrating from 9.3 to 9.5

[thomas veymont]

2016-07-27 11:06 GMT+02:00 Michael Paquier <michael.paqu...@gmail.com>:

> On Wed, Jul 27, 2016 at 5:54 PM, thomas veymont
> <thomas.veym...@gmail.com> wrote:
> > We switched from PostgreSQL server 9.3 to 9.5. From the very beginning
> there
> > was a noticeable drop in performances (for example : when injecting our
> SQL
> > dumps into 9.5, COPY and CREATE INDEX were very slow).
> >
> > Our configuration file was the same for 9.3 and 9.5, except for the
> > "chekpoint segment" that has been deprecated.
>
> Which value are you using for max_wal_size and min_wal_size? And which
> value of checkpoint_segments did you use previously? This could
> influence the checkpoint frequency.
> --
> Michael
>

in 9.3 we had :
checkpoint_segments = 128
#checkpoint_timeout = 5min  # range 30s-1h
checkpoint_completion_target = 0.9   # checkpoint target duration, 0.0 - 1.0
#checkpoint_warning = 30s   # 0 disables

as far as I remember these settings were for faster bulk loading.

in 9.5 we set:
max_wal_size = 6GB  #
https://www.postgresql.org/docs/9.5/static/release-9-5.html, max_wal_size =
(3 * checkpoint_segments) * 16MB
#min_wal_size = 80MB

though I tried max_wal_size = 3GB (default is 1GB) and did not notice any
improvment.

cheers
tom

[GENERAL] low perfomances migrating from 9.3 to 9.5

[thomas veymont]

hello all,

We switched from PostgreSQL server 9.3 to 9.5. From the very beginning
there was a noticeable drop in performances (for example : when injecting
our SQL dumps into 9.5, COPY and CREATE INDEX were very slow).

Our configuration file was the same for 9.3 and 9.5, except for the
"chekpoint segment" that has been deprecated.

I haven't got (yet) some objective performance measurements to show,
because the problem was so obvious (just by looking at the log feed) that
we switched back quickly to 9.3 (production constraints).

What could be the reason for such a problem ?
I thought that, maybe, our system kernel is getting obsolete for a recent
postgresql engine ?
OS is Centos 5.5 kernel 2.6.18-194.el5 #1 SMP x86_64

thanks for suggestions,
Tom

Re: [GENERAL] gaps/overlaps in a time table : current and previous row question

[thomas veymont]

2011/10/6  depst...@alliedtesting.com:
 -Original Message-
 From: pgsql-general-ow...@postgresql.org [mailto:pgsql-general-
 ow...@postgresql.org] On Behalf Of thomas veymont
 Sent: Wednesday, October 05, 2011 5:35 PM
 To: pgsql-general@postgresql.org
 Subject: [GENERAL] gaps/overlaps in a time table : current and previous row
 question

 hello,

 let's say that each rows in a table contains a start time and a end time
 (timeinterval type), but the index are not ordered nor consecutive, e.g :

 $ select * from T order by starttime

 index  | starttime    |   endtime
 -+-+-
 3        |   t1             |  t2
 1        |   t3             |  t4
 18      |   t5             |  t6
 12      |   t7             |  t8

 I want a result that shows time gaps and overlaps in this table, that is :

 delta
 -+
 t3 - t2 |
 t5 - t4 |
 t7 - t6 |

 how would I do that ?

 You can't. The order in which rows are retrieved  from a table is undefined, 
 unless you specify it in your query. If the index cannot be used to specify 
 the order, then there is no way for you to retrieve rows in the correct 
 order.

 If you could get the rows in the correct order, you could use the lag() 
 window function to do what you want.


yes.
there was an answer yesterday about doing this with a window function:
http://archives.postgresql.org/pgsql-general/2011-10/msg00157.php

thanks
tom

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[GENERAL] gaps/overlaps in a time table : current and previous row question

[thomas veymont]

hello,

let's say that each rows in a table contains a start time and a end
time (timeinterval type),
but the index are not ordered nor consecutive, e.g :

$ select * from T order by starttime

index  | starttime|   endtime
-+-+-
3|   t1 |  t2
1|   t3 |  t4
18  |   t5 |  t6
12  |   t7 |  t8

I want a result that shows time gaps and overlaps in this table, that is :

delta
-+
t3 - t2 |
t5 - t4 |
t7 - t6 |

how would I do that ? I guess this could be done with window function and lag()
function but I don't know exactly how. Any suggestion ?

thanks





I guess my question is more about

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