Re: High concurrency same row (inventory)

[MichaelDBA <MichaelDBA@xxxxxxxxxxx>]

Does pg_stat_user_tables validate that the major updates are indeed "hot updates"?  Otherwise, you may be experiencing bloat problems if autovacuum is not set aggressively.  Did you change default parameters for autovacuum?  You should.  They are set very conservatively right outa the box.  Also, I wouldn't increase work_mem too much unless you are experiencing query spill over to disk.  Turn on "log_temp_files" (=0) and monitor if you have this spillover.  If not, don't mess with work_mem.  Also, why isn't effective_cache_size set closer to 80-90% of memory instead of 50%?  Are there other servers on the same host as postgres?  As the other person mentioned, tune checkpoints so that they do not happen too often.  Turn on "log_checkpoints" to get more info.
 
Regards,
Michael Vitale

Rick Otten wrote on 7/29/2019 8:35 AM:

On Mon, Jul 29, 2019 at 2:16 AM Jean Baro <jfbaro@xxxxxxxxx> wrote:

We have a new Inventory system running  on its own database (PG 10 AWS RDS.m5.2xlarge 1TB SSD EBS - Multizone). The DB effective size is less than 10GB at the moment. We provided 1TB to get more IOPS from EBS.

As we don't have a lot of different products in our catalogue it's quite common (especially when a particular product is on sale) to have a high rate of concurrent updates against the same row. There is also a frequent (every 30 minutes) update to all items which changed their current stock/Inventory coming from the warehouses (SAP), the latter is a batch process. We have just installed this system for a new tenant (one of the smallest one) and although it's running great so far, we believe this solution would not scale as we roll out this system to new (and bigger) tenants. Currently there is up to 1.500 transactions per second (mostly SELECTS and 1 particular UPDATE which I believe is the one being aborted/deadlocked some tImes) in this inventory database.

I am not a DBA, but as the DBAs (most of them old school Oracle DBAs who are not happy with the move to POSTGRES) are considering ditching Postgresql without any previous tunning I would like to understand the possibilities.

Considering this is a highly concurrent (same row) system I thought to suggest:

Another thing which you might want to investigate is your checkpoint tunables.  My hunch is with that many writes, the defaults are probably not going to be ideal.

Consider the WAL tunables documentation:  https://www.postgresql.org/docs/10/wal-configuration.html