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* How exactly PostgreSQL allocates memory for its needs?
@ 2010-02-10 05:10 Anton Maksimenkov <anton200@gmail.com>
0 siblings, 1 reply; 3+ messages in thread
From: Anton Maksimenkov @ 2010-02-10 05:10 UTC (permalink / raw)
To: pgsql-performance
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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* Re: How exactly PostgreSQL allocates memory for its needs?
@ 2010-02-10 16:43 Justin Graf <justin@magwerks.com>
parent: Anton Maksimenkov <anton200@gmail.com>
0 siblings, 1 reply; 3+ messages in thread
From: Justin Graf @ 2010-02-10 16:43 UTC (permalink / raw)
To: pgsql-performance; anton200@gmail.com
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: How exactly PostgreSQL allocates memory for its needs?
@ 2010-02-11 03:46 Scott Marlowe <scott.marlowe@gmail.com>
parent: Justin Graf <justin@magwerks.com>
0 siblings, 0 replies; 3+ messages in thread
From: Scott Marlowe @ 2010-02-11 03:46 UTC (permalink / raw)
To: Justin Graf <justin@magwerks.com>; +Cc: pgsql-performance; anton200@gmail.com
On Wed, Feb 10, 2010 at 9:43 AM, Justin Graf <justin@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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2010-02-10 05:10 How exactly PostgreSQL allocates memory for its needs? Anton Maksimenkov <anton200@gmail.com>
2010-02-10 16:43 ` Justin Graf <justin@magwerks.com>
2010-02-11 03:46 ` Scott Marlowe <scott.marlowe@gmail.com>
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