Re: [PERFORM] How exactly PostgreSQL allocates memory for its needs?

[Justin Graf]

On 2/10/2010 12:10 AM, Anton Maksimenkov wrote:
 Can anybody briefly explain me how each postgres process allocate
 memory for it needs?
 I mean, what is the biggest size of malloc() it may want? How many
 such chunks? What is the average size of allocations?

 I think that at first it allocates contiguous piece of shared memory
 for shared buffers (rather big, hundreds of megabytes usually, by
 one chunk).
 What next? temp_buffers, work_mem, maintenance_work_mem - are they
 allocated as contiguous too?
 What about other needs? By what size they are typically allocated?


There  is no short answer to this, you should read section 18 of the manual
http://www.postgresql.org/docs/8.4/interactive/runtime-config.html
specifically section 18.4
http://www.postgresql.org/docs/8.4/interactive/runtime-config-resource.html

and performance section of the wiki
http://wiki.postgresql.org/wiki/Performance_Optimization

Here is a link annotated postgresql.conf
http://www.pgcon.org/2008/schedule/attachments/44_annotated_gucs_draft1.pdf

Keep in mind each connection/client that connecting to the server 
creates a new process on the server.  Each one the settings you list 
above is the max amount of memory each one of those sessions is allowed 
to consume.



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Re: [PERFORM] How exactly PostgreSQL allocates memory for its needs?

[Scott Marlowe]

On Wed, Feb 10, 2010 at 9:43 AM, Justin Graf jus...@magwerks.com wrote:
 Keep in mind each connection/client that connecting to the server
 creates a new process on the server.  Each one the settings you list
 above is the max amount of memory each one of those sessions is allowed
 to consume.

It's even worse for work_mem (formerly sort_mem) in that each
individual hash agg or sort can grab that much memory.  A complex
query with 4 sorts and 2 hash aggregates could chew through 6 x
work_mem if it needed it.  Which is why work_mem can be such a
horrific foot gun.

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[PERFORM] How exactly PostgreSQL allocates memory for its needs?

[Anton Maksimenkov]

Can anybody briefly explain me how each postgres process allocate
memory for it needs?
I mean, what is the biggest size of malloc() it may want? How many
such chunks? What is the average size of allocations?

I think that at first it allocates contiguous piece of shared memory
for shared buffers (rather big, hundreds of megabytes usually, by
one chunk).
What next? temp_buffers, work_mem, maintenance_work_mem - are they
allocated as contiguous too?
What about other needs? By what size they are typically allocated?
-- 
antonvm

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