Hello,
Some days ago I upgraded from 8.4 to 9.3, after the upgrade some queries started performing a lot slower, the query I
amusing in this example is pasted here:
http://pastebin.com/71DjEC21
Considering it is a production database users are complaining because queries are much slower than before, so I tried
todowngrade to 9.2 with the same result as 9.3, I finally restored the database on 8.4 and the query is as fast as
before.
All this tests are done on Debian Squeeze with 2.6.32-5-amd64 kernel version, the hardware is Intel Xeon E5520, 32Gb
ECCRAM, the storage is software RAID 10 with 4 SEAGATE ST3146356SS SAS drives.
postgresql.conf:
max_connections = 250
shared_buffers = 6144MB
temp_buffers = 8MB
max_prepared_transactions = 0
work_mem = 24MB
maintenance_work_mem = 384MB
max_stack_depth = 7MB
default_statistics_target = 150
effective_cache_size = 24576MB
9.3 explain:
http://explain.depesz.com/s/jP7o
9.3 explain analyze:
http://explain.depesz.com/s/6UQT
9.2 explain:
http://explain.depesz.com/s/EW1g
8.4 explain:
http://explain.depesz.com/s/iAba
8.4 explain analyze:
http://explain.depesz.com/s/MPt
It seems to me that the total estimated cost went too high in 9.2 and 9.3 but I am not sure why, I tried commenting out
partof the query and disabling indexonlyscan but still I have very bad timings and estimates.
The dump file is the same for all versions and after the restore process ended I did vacuum analyze on the restored
databasein all versions.
Regards,
Miguel Angel.
