Hi Andres,
Thanks for your reply. What kind of fine tuning we can do in 9.4.7 to overcome this issue – is this a bug that is
addressedin 9.6?
Thanks
Harisankar
On 9/27/17, 5:06 PM, "Andres Freund" <andres@anarazel.de> wrote:
Hi, On 2017-09-27 20:59:33 +0000, harisankar.valiyattil@capitalone.com wrote: > The following bug has been
loggedon the website: > > Bug reference: 14831 > Logged by: Harisankar Valiyattil > Email
address: harisankar.valiyattil@capitalone.com > PostgreSQL version: 9.4.7 > Operating system: linux >
Description: > > We use postgres on amazon RDS. We have a table with close to 15 million data > now and
anapplication is constantly firing some update(insert/update) > operations to this table at around 25 transactions
persecond. the table has > a jsonb column which has a gin index on it; the jonb data has appx 20-40 > attrinbutes
inan average. The application keep on updating data on this > jsonb column. > > While the traffic is running, we
seethat there is a sudden drop in the > write operations (no write happening in DB) causing increase in RDS cpu, >
queuedepth etc. after a few seconds (30 sec, 60 sec) things come back to > normal. If the traffic is constant this
repeatsat constant intervals. > > Our work_mem is 4MB. > > What could be causing this? What kind of
troubleshootingwe can do? What is > the process that runs in the background that causes this intermittant write >
delay? Presumably it's the OS starting to flush dirty buffers to disk, which it periodically does. Not sure if
RDSallows you to monitor that, but the Dirt and Writeback lines in /proc/meminfo would show that. 9.6+ have code
tolimit the amount of dirty buffers in the kernel (enabled by default for background processes, disabled by default
forbackends themseleves). Greetings, Andres Freund
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