Huge Pages - setting the right value

W dniu 2017-03-30 11:45:55 użytkownik pinker <pinker@onet.eu> napisał:

Hi,
I'm currently testing performance with and without huge pages. Documentation
says that in order to estimate the number of huge pages needed one should
check the postmaster's VmPeak value. I wonder if it's only postmaster memory
usage what's matters? Or I could get better estimation from the most memory
intensive postgres process - not necessarly postmaster? I'm using following
command to check it:
for i in $(ps -ef | grep postgres|awk '{print $2}'); do grep ^VmPeak
/proc/${i}/status|awk '{print $2}' >> log; done; sort -n -r log | head -1

I'm asking because some other process takes 606788kB while postmaster only
280444kB.

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or maybe sum of all processes?
I assume that memory allocated by postmaster means shared buffers, so if one wants to huge pages beeing used for sorting as well then should set some bigger number of huge pages in the kernel? Is it a right assumption?

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We are experiencing some performance issues because of high CPU load. So I
would like to ask one more time. The exact question is:
Does PostgreSQL can use huge pages for processes or only for shared buffers?
(Does it make any sense to set the number of huge pages above the
shared_buffers?)
Any help or suggestions would be much appreciated!

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I can't give you an absolutely authoritative answer, but because of the way hugepages are implemented and allocated, I can't think how they could be used for other processes. Linux hugepages are either 2m or 1g, far too large for any likely processes to require. They cannot be allocated in partial pages.

Sent from my iPad

On Jun 11, 2017, at 10:02 AM, pinker <pinker@onet.eu> wrote:

We are experiencing some performance issues because of high CPU load. So I
would like to ask one more time. The exact question is:
Does PostgreSQL can use huge pages for processes or only for shared buffers?
(Does it make any sense to set the number of huge pages above the
shared_buffers?)
Any help or suggestions would be much appreciated!

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Andrew Kerber wrote

I can't give you an absolutely authoritative answer, but because of the
way hugepages are implemented and allocated, I can't think how they could
be used for other processes. Linux hugepages are either 2m or 1g, far too
large for any likely processes to require. They cannot be allocated in
partial pages.

thank you for your help.
My system is using 2MB pages for shared buffers. I have checked and one of
my processes has used 606788kB of memory, so potentially could use ~ 300
huge pages, but does postgres can use it for non shared memory?

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I am sure it does not.

Sent from my iPhone

On Jun 11, 2017, at 10:50 AM, pinker <pinker@onet.eu> wrote:

Andrew Kerber wrote

I can't give you an absolutely authoritative answer, but because of the
way hugepages are implemented and allocated, I can't think how they could
be used for other processes. Linux hugepages are either 2m or 1g, far too
large for any likely processes to require. They cannot be allocated in
partial pages.

thank you for your help.
My system is using 2MB pages for shared buffers. I have checked and one of
my processes has used 606788kB of memory, so potentially could use ~ 300
huge pages, but does postgres can use it for non shared memory?

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2017-06-12 7:52 GMT+12:00 Andrew Kerber <andrew.kerber@gmail.com>:

I am sure it does not.

Sent from my iPhone

On Jun 11, 2017, at 10:50 AM, pinker <pinker@onet.eu> wrote:

Andrew Kerber wrote

I can't give you an absolutely authoritative answer, but because of the
way hugepages are implemented and allocated, I can't think how they

could

be used for other processes. Linux hugepages are either 2m or 1g, far

too

large for any likely processes to require. They cannot be allocated in
partial pages.

thank you for your help.
My system is using 2MB pages for shared buffers. I have checked and one

of

my processes has used 606788kB of memory, so potentially could use ~ 300
huge pages, but does postgres can use it for non shared memory?

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In my case, we had the HugePages enabled but not configured in our Master
DB Server. When we increased the server resources (More RAM & CPU) we had
lots of issues with HugePages. Specially I/O ones. Had to disabled it.

Running Ubuntu 14.04 Server @ Amazon.

Lucas

Was that transparent hugepages or standard hugepages? databases commonly
have problems dealing with transparent hugepages.

On Sun, Jun 11, 2017 at 4:39 PM, Lucas Possamai <drum.lucas@gmail.com>
wrote:

2017-06-12 7:52 GMT+12:00 Andrew Kerber <andrew.kerber@gmail.com>:

I am sure it does not.

Sent from my iPhone

On Jun 11, 2017, at 10:50 AM, pinker <pinker@onet.eu> wrote:

Andrew Kerber wrote

I can't give you an absolutely authoritative answer, but because of the
way hugepages are implemented and allocated, I can't think how they

could

be used for other processes. Linux hugepages are either 2m or 1g, far

too

large for any likely processes to require. They cannot be allocated in
partial pages.

thank you for your help.
My system is using 2MB pages for shared buffers. I have checked and one

of

my processes has used 606788kB of memory, so potentially could use ~ 300
huge pages, but does postgres can use it for non shared memory?

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In my case, we had the HugePages enabled but not configured in our Master
DB Server. When we increased the server resources (More RAM & CPU) we had
lots of issues with HugePages. Specially I/O ones. Had to disabled it.

Running Ubuntu 14.04 Server @ Amazon.

Lucas

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Andrew W. Kerber

'If at first you dont succeed, dont take up skydiving.'

2017-06-12 9:52 GMT+12:00 Andrew Kerber <andrew.kerber@gmail.com>:

Was that transparent hugepages or standard hugepages? databases commonly
have problems dealing with transparent hugepages.

IN my case, it was the Transparent Hugepages....

Lucas

Yes, those should always be disabled using tuned or other methods. Using
tuned is described here (second method). I think the grub.conf method
described is unique to RHEL/OEL/CENTOS.
http://houseofbrick.com/disabling-transparent-hugepages-using-tuned/

On Sun, Jun 11, 2017 at 5:00 PM, Lucas Possamai <drum.lucas@gmail.com>
wrote:

2017-06-12 9:52 GMT+12:00 Andrew Kerber <andrew.kerber@gmail.com>:

Was that transparent hugepages or standard hugepages? databases commonly
have problems dealing with transparent hugepages.

IN my case, it was the Transparent Hugepages....

Lucas

--
Andrew W. Kerber

'If at first you dont succeed, dont take up skydiving.'

standard hugepages, transparent are disabled.
They were set exactly following the procedure from postgres documentation.

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