Re: work_mem and shared_buffers question

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