Thread: Swapping on Solaris
Hello,
I'm running PostgreSQL on a Solaris 8 system with 2GB of RAM and I'm
having some difficulty getting PostgreSQL to use the available RAM. My RAM
settings in postgresql.conf are
shared_buffers = 8192 # min 16, at least max_connections*2, 8KB each
sort_mem = 131072 # min 64, size in KB
vacuum_mem = 131072 # min 1024, size in KB
Ignoring the fact that the sort and vacuum numbers are really high, this is
what Solaris shows me when running top:
Memory: 2048M real, 1376M free, 491M swap in use, 2955M swap free
For some reason I have 1.25GB of free RAM but PostgreSQL seems compelled to
swap to the hard drive rather than use that RAM. I have the shared buffers
set as high as the Solaris kernel will let me. I also know that Solaris
will cache frequently used files in RAM, thereby lowering the amount of RAM
available to an application, but my understanding is that Solaris will dump
that cache if an application or the kernel itself requires it.
The system has about 1,000 active email users using unix mailboxes which
could what is keeping the database from exploiting as much RAM as available
but my primary concern is to allow PostgreSQL to use as much RAM as it
requires without swapping.
What can I do to force the system to allow PostgreSQL to do this?
Regards,
Kevin Schroeder
Kevin Schroeder wrote: > > > Ignoring the fact that the sort and vacuum numbers are really high, this > is what Solaris shows me when running top: > > Memory: 2048M real, 1376M free, 491M swap in use, 2955M swap free > Maybe check the swap usage with 'swap -l' which reports reliably if any (device or file) swap is actually used. I think Solaris 'top' does some strange accounting to calculate the 'swap in use' value (like including used memory). It looks to me like you are using no (device or file) swap at all, and have 1.3G of real memory free, so could in fact give Postgres more of it :-) regards Mark
> Kevin Schroeder wrote: > It looks to me like you are using no (device or file) swap at all, and > have 1.3G of real memory free, so could in fact give Postgres more of it :-) > Indeed. If you DO run into trouble after giving Postgres more RAM, use the vmstat command. You can use this command like "vmstat 10". (ignore the first line) Keep an eye on the "pi" and "po" parameters. (kilobytes paged in and out) HTH, Matt ------ Matt Casters <matt.casters@ibridge.be> i-Bridge bvba, http://www.kettle.be Fonteinstraat 70, 9400 Okegem, Belgium Phone +32 (0) 486/97.29.37
Mark Kirkwood wrote: > Kevin Schroeder wrote: > >> >> >> Ignoring the fact that the sort and vacuum numbers are really high, >> this is what Solaris shows me when running top: >> >> Memory: 2048M real, 1376M free, 491M swap in use, 2955M swap free >> > Maybe check the swap usage with 'swap -l' which reports reliably if any > (device or file) swap is actually used. > > I think Solaris 'top' does some strange accounting to calculate the > 'swap in use' value (like including used memory). > > It looks to me like you are using no (device or file) swap at all, and > have 1.3G of real memory free, so could in fact give Postgres more of > it :-) I suspect that "free" memory is in fact being used for the file system cache. There were some changes in the meaning of "free" in Solaris 8 and 9. The memstat command gives a nice picture of memory usage on the system. I don't think memstat came with Solaris 8, but you can get it from solarisinternals.com. The Solaris Internals book is an excellent read as well; it explains all of this in gory detail. Note that files in /tmp are usually in a tmpfs file system. These files may be the usage of swap that you're seeing (as they will be paged out on an active system with some memory pressure) Finally, just as everyone suggests upgrading to newer postgresql releases, you probably want to get to a newer Solaris release. -- Alan
po and pi are relatively low, but do pick up when there's an increase in activity. I am seeing a lot of "minor faults", though. vmstat -S 5 reports [9:38am]# vmstat -S 5 procs memory page disk faults cpu r b w swap free si so pi po fr de sr s0 s1 s3 -- in sy cs us sy id 0 0 0 3235616 1414536 0 0 303 11 10 0 0 6 24 0 0 13 192 461 17 11 72 1 0 0 3004376 1274912 0 0 0 0 0 0 0 3 16 0 0 494 1147 441 52 25 23 494 in faults 1147 sy faults Generally faults are a bad thing. Is that the case here? Kevin ----- Original Message ----- From: "Matt Casters" <Matt.Casters@advalvas.be> To: <pgsql-performance@postgresql.org> Sent: Wednesday, January 19, 2005 3:57 AM Subject: Re: [PERFORM] Swapping on Solaris > Kevin Schroeder wrote: > It looks to me like you are using no (device or file) swap at all, and > have 1.3G of real memory free, so could in fact give Postgres more of it > :-) > Indeed. If you DO run into trouble after giving Postgres more RAM, use the vmstat command. You can use this command like "vmstat 10". (ignore the first line) Keep an eye on the "pi" and "po" parameters. (kilobytes paged in and out) HTH, Matt ------ Matt Casters <matt.casters@ibridge.be> i-Bridge bvba, http://www.kettle.be Fonteinstraat 70, 9400 Okegem, Belgium Phone +32 (0) 486/97.29.37 ---------------------------(end of broadcast)--------------------------- TIP 2: you can get off all lists at once with the unregister command (send "unregister YourEmailAddressHere" to majordomo@postgresql.org)
I take that back. There actually is some paging going on. I ran sar -g 5 10 and when a request was made (totally about 10 DB queries) my pgout/s jumped to 5.8 and my ppgout/s jumped to 121.8. pgfree/s also jumped to 121.80. Kevin ----- Original Message ----- From: "Matt Casters" <Matt.Casters@advalvas.be> To: <pgsql-performance@postgresql.org> Sent: Wednesday, January 19, 2005 3:57 AM Subject: Re: [PERFORM] Swapping on Solaris > Kevin Schroeder wrote: > It looks to me like you are using no (device or file) swap at all, and > have 1.3G of real memory free, so could in fact give Postgres more of it > :-) > Indeed. If you DO run into trouble after giving Postgres more RAM, use the vmstat command. You can use this command like "vmstat 10". (ignore the first line) Keep an eye on the "pi" and "po" parameters. (kilobytes paged in and out) HTH, Matt ------ Matt Casters <matt.casters@ibridge.be> i-Bridge bvba, http://www.kettle.be Fonteinstraat 70, 9400 Okegem, Belgium Phone +32 (0) 486/97.29.37 ---------------------------(end of broadcast)--------------------------- TIP 2: you can get off all lists at once with the unregister command (send "unregister YourEmailAddressHere" to majordomo@postgresql.org)
I suspect that the memory is being used to cache files as well since the email boxes are using unix mailboxes, for the time being. With people checking their email sometimes once per minute I can see why Solaris would want to cache those files. Perhaps my question would be more appropriate to a Solaris mailing list since what I really want to do is get Solaris to simply allow PostgreSQL to use more RAM and reduce the amount of RAM used for file caching. I would have thought that Solaris gives some deference to a running application that's being swapped than for a file cache. Is there any way to set custom parameters on Solaris' file-caching behavior to allow PostgreSQL to use more physical RAM? I will also check out memstat. It's not on my system, but I'll get it from the site you noted. Thanks Kevin ----- Original Message ----- From: "Alan Stange" <stange@rentec.com> Cc: "Kevin Schroeder" <kschroeder@mirageworks.com>; <pgsql-performance@postgresql.org> Sent: Wednesday, January 19, 2005 7:51 AM Subject: Re: [PERFORM] Swapping on Solaris > Mark Kirkwood wrote: > >> Kevin Schroeder wrote: >> >>> >>> >>> Ignoring the fact that the sort and vacuum numbers are really high, this >>> is what Solaris shows me when running top: >>> >>> Memory: 2048M real, 1376M free, 491M swap in use, 2955M swap free >>> >> Maybe check the swap usage with 'swap -l' which reports reliably if any >> (device or file) swap is actually used. >> >> I think Solaris 'top' does some strange accounting to calculate the >> 'swap in use' value (like including used memory). >> >> It looks to me like you are using no (device or file) swap at all, and >> have 1.3G of real memory free, so could in fact give Postgres more of it >> :-) > > I suspect that "free" memory is in fact being used for the file system > cache. There were some changes in the meaning of "free" in Solaris 8 and > 9. The memstat command gives a nice picture of memory usage on the > system. I don't think memstat came with Solaris 8, but you can get it > from solarisinternals.com. The Solaris Internals book is an excellent > read as well; it explains all of this in gory detail. > Note that files in /tmp are usually in a tmpfs file system. These files > may be the usage of swap that you're seeing (as they will be paged out on > an active system with some memory pressure) > > Finally, just as everyone suggests upgrading to newer postgresql releases, > you probably want to get to a newer Solaris release. > -- Alan > > >
/tmp doesn't seem to be much of a problem. I have about 1k worth of data in there and 72k in /var/tmp. Would turning swap off help in tuning the database in this regard? top is reporting that there's 1.25GB of RAM free on a 2GB system so, in my estimation, there's no need for PostgreSQL to be swapped unless that free memory is Solaris caching files in RAM. Kevin ----- Original Message ----- From: "Greg Spiegelberg" <gspiegelberg@cranel.com> To: <stange@rentec.com> Cc: "Kevin Schroeder" <kschroeder@mirageworks.com>; <pgsql-performance@postgresql.org> Sent: Wednesday, January 19, 2005 9:07 AM Subject: Re: [PERFORM] Swapping on Solaris > Alan Stange wrote: >> >> Note that files in /tmp are usually in a tmpfs file system. These files >> may be the usage of swap that you're seeing (as they will be paged out on >> an active system with some memory pressure) > > You can do a couple things with /tmp. Create a separate file system > for it so it will have zero impact on swap and use the "noatime" mount > option. Alternatively, limit the size of /tmp using the mount option > "size=MBm" replacing "MB" with the size you want it to be in MBytes. If > your application uses /tmp heavily, be sure to put it on a speedy, > local LUN. > > >> Finally, just as everyone suggests upgrading to newer postgresql >> releases, you probably want to get to a newer Solaris release. > > If you really want to avoid swapping I'd suggest tuning your database > first with swap turned off and put it under a "normal" load while > watching both top and vmstat. When you're happy with it, turn swap > back on for those "heavy" load times and move on. > > Greg > > -- > Greg Spiegelberg > Product Development Manager > Cranel, Incorporated. > Phone: 614.318.4314 > Fax: 614.431.8388 > Email: gspiegelberg@cranel.com > Technology. Integrity. Focus. > > > >
Kevin Schroeder wrote: > I suspect that the memory is being used to cache files as well since > the email boxes are using unix mailboxes, for the time being. With > people checking their email sometimes once per minute I can see why > Solaris would want to cache those files. Perhaps my question would be > more appropriate to a Solaris mailing list since what I really want to > do is get Solaris to simply allow PostgreSQL to use more RAM and > reduce the amount of RAM used for file caching. I would have thought > that Solaris gives some deference to a running application that's > being swapped than for a file cache. > > Is there any way to set custom parameters on Solaris' file-caching > behavior to allow PostgreSQL to use more physical RAM? Your explanation doesn't sound quite correct. If postgresql malloc()'s some memory and uses it, the file cache will be reduced in size and the memory given to postgresql. But if postgresql doesn't ask for or use the memory, then solaris is going to use it for something else. There's nothing in Solaris that doesn't "allow" postgresql to use more RAM. -- Alan
Alan Stange wrote: > > Note that files in /tmp are usually in a tmpfs file system. These > files may be the usage of swap that you're seeing (as they will be paged > out on an active system with some memory pressure) You can do a couple things with /tmp. Create a separate file system for it so it will have zero impact on swap and use the "noatime" mount option. Alternatively, limit the size of /tmp using the mount option "size=MBm" replacing "MB" with the size you want it to be in MBytes. If your application uses /tmp heavily, be sure to put it on a speedy, local LUN. > Finally, just as everyone suggests upgrading to newer postgresql > releases, you probably want to get to a newer Solaris release. If you really want to avoid swapping I'd suggest tuning your database first with swap turned off and put it under a "normal" load while watching both top and vmstat. When you're happy with it, turn swap back on for those "heavy" load times and move on. Greg -- Greg Spiegelberg Product Development Manager Cranel, Incorporated. Phone: 614.318.4314 Fax: 614.431.8388 Email: gspiegelberg@cranel.com Technology. Integrity. Focus.
Maybe, I'm just seeing a problem where none exists. I ran sar -w 3 100 and I actually did not see any swap activity despite the fact that I've got 500+MB of swap file being used. Kevin ----- Original Message ----- From: "Alan Stange" <stange@rentec.com> To: "Kevin Schroeder" <kschroeder@mirageworks.com> Cc: <pgsql-performance@postgresql.org> Sent: Wednesday, January 19, 2005 9:42 AM Subject: Re: [PERFORM] Swapping on Solaris > Kevin Schroeder wrote: > >> I take that back. There actually is some paging going on. I ran sar -g >> 5 10 and when a request was made (totally about 10 DB queries) my pgout/s >> jumped to 5.8 and my ppgout/s jumped to 121.8. pgfree/s also jumped to >> 121.80. > > I'm fairly sure that the pi and po numbers include file IO in Solaris, > because of the unified VM and file systems. > > -- Alan > > >
Kevin Schroeder wrote: > I take that back. There actually is some paging going on. I ran sar > -g 5 10 and when a request was made (totally about 10 DB queries) my > pgout/s jumped to 5.8 and my ppgout/s jumped to 121.8. pgfree/s also > jumped to 121.80. I'm fairly sure that the pi and po numbers include file IO in Solaris, because of the unified VM and file systems. -- Alan
I may be asking the question the wrong way, but when I start up PostgreSQL swap is what gets used the most of. I've got 1282MB free RAM right now and and 515MB swap in use. Granted, swap file usage probably wouldn't be zero, but I would guess that it should be a lot lower so something must be keeping PostgreSQL from using the free RAM that my system is reporting. For example, one of my postgres processes is 201M in size but on 72M is resident in RAM. That extra 130M is available in RAM, according to top, but postgres isn't using it. Kevin ----- Original Message ----- From: "Alan Stange" <stange@rentec.com> To: "Kevin Schroeder" <kschroeder@mirageworks.com> Cc: <pgsql-performance@postgresql.org> Sent: Wednesday, January 19, 2005 9:30 AM Subject: Re: [PERFORM] Swapping on Solaris > Kevin Schroeder wrote: > >> I suspect that the memory is being used to cache files as well since the >> email boxes are using unix mailboxes, for the time being. With people >> checking their email sometimes once per minute I can see why Solaris >> would want to cache those files. Perhaps my question would be more >> appropriate to a Solaris mailing list since what I really want to do is >> get Solaris to simply allow PostgreSQL to use more RAM and reduce the >> amount of RAM used for file caching. I would have thought that Solaris >> gives some deference to a running application that's being swapped than >> for a file cache. >> >> Is there any way to set custom parameters on Solaris' file-caching >> behavior to allow PostgreSQL to use more physical RAM? > > Your explanation doesn't sound quite correct. If postgresql malloc()'s > some memory and uses it, the file cache will be reduced in size and the > memory given to postgresql. But if postgresql doesn't ask for or use the > memory, then solaris is going to use it for something else. There's > nothing in Solaris that doesn't "allow" postgresql to use more RAM. > > -- Alan > > >
On Jan 19, 2005, at 10:42 AM, Alan Stange wrote: > Kevin Schroeder wrote: > >> I take that back. There actually is some paging going on. I ran sar >> -g 5 10 and when a request was made (totally about 10 DB queries) my >> pgout/s jumped to 5.8 and my ppgout/s jumped to 121.8. pgfree/s also >> jumped to 121.80. > > I'm fairly sure that the pi and po numbers include file IO in Solaris, > because of the unified VM and file systems. Curiously, what are your shared_buffers and sort_mem set too? Perhaps they are too high? -- Jeff Trout <jeff@jefftrout.com> http://www.jefftrout.com/ http://www.stuarthamm.net/
I think it's probably just reserving them. I can't think of anything else. Also, when I run swap activity with sar I don't see any activity, which also points to reserved swap space, not used swap space. swap -s reports total: 358336k bytes allocated + 181144k reserved = 539480k used, 2988840k available Kevin ----- Original Message ----- From: "Alan Stange" <stange@rentec.com> To: "Kevin Schroeder" <kschroeder@mirageworks.com> Cc: <pgsql-performance@postgresql.org> Sent: Wednesday, January 19, 2005 11:04 AM Subject: Re: [PERFORM] Swapping on Solaris > Kevin Schroeder wrote: > >> I may be asking the question the wrong way, but when I start up >> PostgreSQL swap is what gets used the most of. I've got 1282MB free RAM >> right now and and 515MB swap in use. Granted, swap file usage probably >> wouldn't be zero, but I would guess that it should be a lot lower so >> something must be keeping PostgreSQL from using the free RAM that my >> system is reporting. For example, one of my postgres processes is 201M >> in size but on 72M is resident in RAM. That extra 130M is available in >> RAM, according to top, but postgres isn't using it. > > The test you're doing doesn't measure what you think you're measuring. > > First, what else is running on the machine? Note that some shared > memory allocations do reserve backing pages in swap, even though the pages > aren't currently in use. Perhaps this is what you're measuring? > "swap -s" has better numbers than top. > > You'd be better by trying a reboot then starting pgsql and seeing what > memory is used. > > Just because you start a process and see the swap number increase doesn't > mean that the new process is in swap. It means some anonymous pages had > to be evicted to swap to make room for the new process or some pages had > to be reserved in swap for future use. Typically a new process won't be > paged out unless something else is causing enormous memory pressure... > > -- Alan > > >
Kevin Schroeder wrote: > I may be asking the question the wrong way, but when I start up > PostgreSQL swap is what gets used the most of. I've got 1282MB free > RAM right now and and 515MB swap in use. Granted, swap file usage > probably wouldn't be zero, but I would guess that it should be a lot > lower so something must be keeping PostgreSQL from using the free RAM > that my system is reporting. For example, one of my postgres > processes is 201M in size but on 72M is resident in RAM. That extra > 130M is available in RAM, according to top, but postgres isn't using it. The test you're doing doesn't measure what you think you're measuring. First, what else is running on the machine? Note that some shared memory allocations do reserve backing pages in swap, even though the pages aren't currently in use. Perhaps this is what you're measuring? "swap -s" has better numbers than top. You'd be better by trying a reboot then starting pgsql and seeing what memory is used. Just because you start a process and see the swap number increase doesn't mean that the new process is in swap. It means some anonymous pages had to be evicted to swap to make room for the new process or some pages had to be reserved in swap for future use. Typically a new process won't be paged out unless something else is causing enormous memory pressure... -- Alan
On Jan 19, 2005, at 10:40 AM, Kevin Schroeder wrote: > I may be asking the question the wrong way, but when I start up > PostgreSQL swap is what gets used the most of. I've got 1282MB free > RAM right now and and 515MB swap in use. Granted, swap file usage > probably wouldn't be zero, but I would guess that it should be a lot > lower so something must be keeping PostgreSQL from using the free RAM > that my system is reporting. For example, one of my postgres > processes is 201M in size but on 72M is resident in RAM. That extra > 130M is available in RAM, according to top, but postgres isn't using > it. Can you please give us your exact shared_buffer and sort_mem settings? This will help greatly. As a general thing, we say don't use more than 10k shared bufs unless you have done testing and enjoy a benefit. Managing all those buffers isn't free. I'm also not sure how Solaris reports shared memory usage for apps... a lot of that could be shared mem. Can you watch say, vmstat 1 for a minute or two while PG is running and see if you're actually swapping? -- Jeff Trout <jeff@jefftrout.com> http://www.jefftrout.com/ http://www.stuarthamm.net/
This page may be of use: http://www.serverworldmagazine.com/monthly/2003/02/solaris.shtml From personal experience, for god's sake don't think Solaris' VM/swap implementation is easy - it's damn good, but it ain't easy! Matt Kevin Schroeder wrote: > I think it's probably just reserving them. I can't think of anything > else. Also, when I run swap activity with sar I don't see any > activity, which also points to reserved swap space, not used swap space. > > swap -s reports > > total: 358336k bytes allocated + 181144k reserved = 539480k used, > 2988840k available > > Kevin > > ----- Original Message ----- From: "Alan Stange" <stange@rentec.com> > To: "Kevin Schroeder" <kschroeder@mirageworks.com> > Cc: <pgsql-performance@postgresql.org> > Sent: Wednesday, January 19, 2005 11:04 AM > Subject: Re: [PERFORM] Swapping on Solaris > > >> Kevin Schroeder wrote: >> >>> I may be asking the question the wrong way, but when I start up >>> PostgreSQL swap is what gets used the most of. I've got 1282MB free >>> RAM right now and and 515MB swap in use. Granted, swap file usage >>> probably wouldn't be zero, but I would guess that it should be a lot >>> lower so something must be keeping PostgreSQL from using the free >>> RAM that my system is reporting. For example, one of my postgres >>> processes is 201M in size but on 72M is resident in RAM. That extra >>> 130M is available in RAM, according to top, but postgres isn't using >>> it. >> >> >> The test you're doing doesn't measure what you think you're measuring. >> >> First, what else is running on the machine? Note that some shared >> memory allocations do reserve backing pages in swap, even though the >> pages aren't currently in use. Perhaps this is what you're >> measuring? "swap -s" has better numbers than top. >> >> You'd be better by trying a reboot then starting pgsql and seeing >> what memory is used. >> >> Just because you start a process and see the swap number increase >> doesn't mean that the new process is in swap. It means some >> anonymous pages had to be evicted to swap to make room for the new >> process or some pages had to be reserved in swap for future use. >> Typically a new process won't be paged out unless something else is >> causing enormous memory pressure... >> >> -- Alan >> >> >> > > > ---------------------------(end of broadcast)--------------------------- > TIP 3: if posting/reading through Usenet, please send an appropriate > subscribe-nomail command to majordomo@postgresql.org so that your > message can get through to the mailing list cleanly
Well, easy it ain't and I believe it's good. One final question: When I run sar -w I get no swap activity, but the process switch column registers between 400 and 700 switches per second. Would that be in the normal range for a medium-use system? Thanks Kevin ----- Original Message ----- From: "Matt Clark" <matt@ymogen.net> To: "Kevin Schroeder" <kschroeder@mirageworks.com> Cc: <pgsql-performance@postgresql.org> Sent: Wednesday, January 19, 2005 1:01 PM Subject: Re: [PERFORM] Swapping on Solaris > This page may be of use: > > http://www.serverworldmagazine.com/monthly/2003/02/solaris.shtml > > From personal experience, for god's sake don't think Solaris' VM/swap > implementation is easy - it's damn good, but it ain't easy! > > Matt > > Kevin Schroeder wrote: > >> I think it's probably just reserving them. I can't think of anything >> else. Also, when I run swap activity with sar I don't see any activity, >> which also points to reserved swap space, not used swap space. >> >> swap -s reports >> >> total: 358336k bytes allocated + 181144k reserved = 539480k used, >> 2988840k available >> >> Kevin >> >> ----- Original Message ----- From: "Alan Stange" <stange@rentec.com> >> To: "Kevin Schroeder" <kschroeder@mirageworks.com> >> Cc: <pgsql-performance@postgresql.org> >> Sent: Wednesday, January 19, 2005 11:04 AM >> Subject: Re: [PERFORM] Swapping on Solaris >> >> >>> Kevin Schroeder wrote: >>> >>>> I may be asking the question the wrong way, but when I start up >>>> PostgreSQL swap is what gets used the most of. I've got 1282MB free >>>> RAM right now and and 515MB swap in use. Granted, swap file usage >>>> probably wouldn't be zero, but I would guess that it should be a lot >>>> lower so something must be keeping PostgreSQL from using the free RAM >>>> that my system is reporting. For example, one of my postgres processes >>>> is 201M in size but on 72M is resident in RAM. That extra 130M is >>>> available in RAM, according to top, but postgres isn't using it. >>> >>> >>> The test you're doing doesn't measure what you think you're measuring. >>> >>> First, what else is running on the machine? Note that some shared >>> memory allocations do reserve backing pages in swap, even though the >>> pages aren't currently in use. Perhaps this is what you're measuring? >>> "swap -s" has better numbers than top. >>> >>> You'd be better by trying a reboot then starting pgsql and seeing what >>> memory is used. >>> >>> Just because you start a process and see the swap number increase >>> doesn't mean that the new process is in swap. It means some anonymous >>> pages had to be evicted to swap to make room for the new process or some >>> pages had to be reserved in swap for future use. Typically a new >>> process won't be paged out unless something else is causing enormous >>> memory pressure... >>> >>> -- Alan >>> >>> >>> >> >> >> ---------------------------(end of broadcast)--------------------------- >> TIP 3: if posting/reading through Usenet, please send an appropriate >> subscribe-nomail command to majordomo@postgresql.org so that your >> message can get through to the mailing list cleanly > > > >
On Wed, 2005-01-19 at 09:40 -0600, Kevin Schroeder wrote: > I may be asking the question the wrong way, but when I start up PostgreSQL > swap is what gets used the most of. I've got 1282MB free RAM right now and > and 515MB swap in use. Granted, swap file usage probably wouldn't be zero, > but I would guess that it should be a lot lower so something must be keeping > PostgreSQL from using the free RAM that my system is reporting. For > example, one of my postgres processes is 201M in size but on 72M is resident > in RAM. That extra 130M is available in RAM, according to top, but postgres > isn't using it. You probably need to look at the way Solaris memory allocation works. On Linux 2.6, my understanding is that if a process allocates memory, but doesn't actually use it, then the OS is smart enough to swap the overallocated portion out to swap. The effect of that is that the program stays happy because it has all the "memory" it thinks it needs, while the OS is happy because it conserves it valuable physical RAM for memory that is actually being used. If what I say is correct, you should actually observe very low swapping I/O rates on the system. Anyway, look at how the algorithms work if you are worried by what you see. But mostly, if the system is performing OK, then no need to worry - if your only measure of that is system performance data then you need to instrument your application better, so you can look at the data that really matters. -- Best Regards, Simon Riggs
On Wed, Jan 19, 2005 at 10:42:26AM -0500, Alan Stange wrote:
>
> I'm fairly sure that the pi and po numbers include file IO in Solaris,
> because of the unified VM and file systems.
That's correct.
A
--
Andrew Sullivan | ajs@crankycanuck.ca
When my information changes, I alter my conclusions. What do you do sir?
--attr. John Maynard Keynes
Andrew Sullivan wrote: > On Wed, Jan 19, 2005 at 10:42:26AM -0500, Alan Stange wrote: > > > > I'm fairly sure that the pi and po numbers include file IO in Solaris, > > because of the unified VM and file systems. > > That's correct. I have seen cases on BSDs where 'pi' includes page-faulting in the executables from the file system, but Solaris actually has 'po' as filesystem I/O. That is a new one to me. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073