Re: [BUGS] BUG #14831: Intermittent write blocks

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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