Re: work_mem and shared_buffers question

No, as I said, as per my observation your connection will not use your
work mem unless there is a sort happening,

but

Yes, every connection uses certain amount of RAM, some documents say it 5
MB and some say it is 1.9 MB.

Expert review may be needed on my observation.

On Mon, 10 Feb, 2020, 4:00 PM Ayub M, <hiayub(at)gmail(dot)com> wrote:

> Thanks, for q2 - if work_mem is a limit before spilling onto disk, is
> there a min amount of memory which gets allocated to each session when it
> starts?
>
> On Mon, Feb 10, 2020 at 3:51 AM Naresh g <naresh5310(at)gmail(dot)com> wrote:
>
>> 1. Yes, by default it is advisable to set 25% of RAM to shared buffers
>> because community version postgres highly depends on OS cache, which means
>> when you fetch something from disk, it is first copied to OS cache (75%)
>> then to shared buffers(25%).
>> Two copies of data will be there in your system RAM.
>> The copy is called buffered IO.
>>
>> Amazon Aurora eliminates this buffered IO, hence it is not required you
>> stick to restrict 25% of RAM.
>>
>> 2. Work_mem is just setting, if you sort something out your session uses
>> than memory other wise it just lies at OS.
>>
>> On Mon, 10 Feb, 2020, 1:34 PM Ayub M, <hiayub(at)gmail(dot)com> wrote:
>>
>>>
>>> 1. shared_buffers - In a regular PostgreSQL installation, say I am
>>> allocating 25% of my memory to shared_buffers that means it leaves 75% for
>>> rest such as OS, page cache and work_mems etc. Is my understanding correct?
>>> If so, AWS Aurora for Postgres uses 75% of memory for shared_buffers, then
>>> it would leave just 25% for other things?
>>> 2. Does the memory specified for work_mem, fully gets allocated to
>>> all sessions irrespective of whether they do any sorting or hashing
>>> operations?
>>>
>>>
>>> --
>>> Regards,
>>> Ayub
>>>
>>
>
> --
> Regards,
> Ayub
>