Re: Performance comparison between Pgsql 10.5 and Pgsql 11.2 - Mailing list pgsql-general

So the first file is on Postgres11.2 on a test server (and where I compare 10 vs 11)

The second file, is our preprod machine running Postgres 11.2 (different hardware etc, it is a VM). I know that could be confusing, but I just wanted to compare that too because if you see the two files there's a lot of difference between the two machines.

And they are both running CentOS 7.

So at this point I have two problems. One inside the machine between Postgres 10 and 11 and another problem on the preprod (similar to prod) with a lot of lseek.

Sorry if this is confusing, hope it is clear now.

Regarding partitions/tables. The first file involves just one table. The second file (with a huge lseek) was running the test on a single table, but meanwhile it was accessible by the preprod web application. So it was maybe hit by some user and some other table.

Question:

1) Is it possible that pgbench could not be really a good tool for testing the performances? If I use a sql script of thousands of insert records and compare on the same server between pg10 and pg11 I get pretty much the same result (maybe better on pg11)

2) regarding preprod, is there any way to reduce those lseek()?  Just to let you know, comparing the same insert script between the first server, the first server takes 2m the second one takes 5-7m.

Thanks a lot,

Il giorno gio 7 mar 2019 alle ore 04:47 Thomas Munro <thomas.munro@gmail.com> ha scritto:

On Thu, Mar 7, 2019 at 12:12 AM Nicola Contu <nicola.contu@gmail.com> wrote:
> This is instead the strace of another server running the same version compiled  but that is even slower.

Huh.  That's a lot of lseek().  Some of these will be for random
reads/writes and will go way in v12, and some will be for probing the
size of relations while planning, and some while executing scans.  I
bet you could make some of them go away by using prepared statements.
Does the query in your test involve many partitions/tables?

% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 32.50  143.010306           7  21044095           lseek
 26.21  115.354045          14   8144577           read
  6.18   27.185578          16   1669889        10 sendto
  5.29   23.300584          57    407528           fdatasync
  4.93   21.709522           9   2313529    824174 recvfrom
  3.31   14.547568          19    765897           write
  2.73   12.007486          14    867088     14494 epoll_wait
  2.18    9.597460          15    659871     84097 futex
  1.85    8.147759          14    567414           close
  1.77    7.767832          18    437656     11319 open

The other results had 1 usec lseek(), and much fewer of them relative
to the number of reads and writes.  BTW, are you comparing v10 and v11
on the same hardware, kernel, filesystem?  Just wondering if there
could be some change in syscall overhead on different kernel patch
levels or something like that: we see 7 usec vs 1 usec in those two
files (though I have no idea how reliable these times are) and if
we're going to call it 21 million times at some point it might
matter...

--
Thomas Munro
https://enterprisedb.com