Re: DB Server slow down & hang during Peak hours of Usage - Mailing list pgsql-general

also,

checkpoint setup are all default values

you may try to 

checkpoint_completion_target = 0.9

checkpoint_timeout = 15min

max_wal_size = 5GB

and, as said in the previous mail, check the checkpoint logs 

Also, all vacuum and autovacuum values are defaults

so, as autovacuum_work_mem = -1

the autovacuum processes will use the 4 GB setuped by maintenance_work_mem = 4096MB

as there are 3 launched at the same time, its 12 GB "eaten"

which doesn't look like a good idea, so set

autovacuum_work_mem = 128MB

also pls read the autovacuum doc for your version (which is ?) here for postgres 12:

https://www.postgresql.org/docs/12/runtime-config-autovacuum.html

Marc MILLAS

Senior Architect

+33607850334

www.mokadb.com

On Tue, Aug 8, 2023 at 1:59 PM Marc Millas <marc.millas@mokadb.com> wrote:

Hello,

in the postgresql.conf joined, 2 things (at least) look strange:

1) the values for background writer are the default values, fit for a server with a limited writes throughput.

you may want to increase those, like:

bgwriter_delay = 50ms

bgwriter_lru_maxpages = 400

bgwriter_lru_multiplier = 4.0 

and check the checkpoint log to see if there are still backend processes writes.

2) work_mem is set to 2 GB.

so, if 50 simultaneous requests use at least one buffer for sorting, joining, ..., you will consume 100 GB of RAM

this value seems huge for the kind of config/usage you describe.

You may try to set work_mem to 100 MB and check what's happening.

Also check the logs, postgres tells his life there...

Marc MILLAS

Senior Architect

+33607850334

www.mokadb.com

On Mon, Aug 7, 2023 at 3:36 PM KK CHN <kkchn.in@gmail.com> wrote:

List ,

Description:

Maintaining a DB Server Postgres and with a lot of read writes to this Server( virtual machine running on  ESXi 7 with CentOS 7) . 

( I am not sure how to get the read / write counts or required IOPS or any other parameters for you. If  you point our  I can execute those commands and get the data. ) 

Peak hours  say 19:00 Hrs to 21:00 hrs it hangs ( The application is an Emergency call response system  writing many  Emergency Response vehicles locations coordinates to the DB every 30 Seconds and every emergency call metadata (username, phone number, location info and address of the caller to the DB for each call)  

During these hours  the system hangs and the  Application ( which shows the location of the vehicles on a  GIS map hangs ) and the CAD machines which connects to the system hangs as those machines can't  connect to the DB and get data for displaying the caller information to the call taking persons working on them. )

Issue : 

How to trace out what makes this DB  hangs and make it slow  and how to fix it..

Resource poured on the system :

64 vCPUs  allocate ( Out of a host machine comprised of 2 processor slots of 20 cores each with Hyper Threading, intel xeon 2nd Gen, CPU usage show 50 % in vCentre Console), and RAM 64 GB allocated ( buy usage always showing around 33 GB only ) 

Query :

How to rectify the issues that makes the DB server underperforming and find a permanent fix for this slow down issue. 

Attached the  Postgres.conf file here for reference .

Any more information required I can share for analysis to fix the issue. 

Krishane