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* Big difference in databasesize compared with disksize
@ 2012-02-14 13:22 Bernhard Schrader <bernhard.schrader@innogames.de>
0 siblings, 1 reply; 3+ messages in thread
From: Bernhard Schrader @ 2012-02-14 13:22 UTC (permalink / raw)
To: pgsql-admin
Hi all,
Problem:
If I use
SELECT pg_size_pretty(pg_database_size('dbname')) As fulldbsize;
fulldbsize
------------
6455 MB
(1 row)
If I compare this output with
/var/lib/postgresql/9.0/main/base/[DBFOLDER]
I have a difference of 3 GB, which I think is not normal.
To make a little bit clearer what i mean:
/var/lib/postgresql/9.0/main/base/43169# du --apparent-size -h
6.4G .
/var/lib/postgresql/9.0/main/base/43169# du -sh
9.4G .
Is such a big fragmentation a normal behavior? It's splitted to several
Filenodes.
I also made a "xfs_fsr" to defrag all of this, i gathered around 1 GB
back ( would be more if the tables wouldn't be written in this time )
But within some hours the fragmentation was back..
There is also no big dead tuple count in this database, it's getting a
vacuum analyze every night.
Right now i am out of ideas... What do you think i could do?
If you need more information i can provide.
Environment:
- OS: Debian Lenny
- Disksize: 15GB
- Filesystem: XFS
- Psql: 9.0.3
thanks in advance.
regards
Bernhard
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Big difference in databasesize compared with disksize
@ 2012-02-17 09:57 Bernhard Schrader <bernhard.schrader@innogames.de>
parent: Bernhard Schrader <bernhard.schrader@innogames.de>
0 siblings, 1 reply; 3+ messages in thread
From: Bernhard Schrader @ 2012-02-17 09:57 UTC (permalink / raw)
To: pgsql-admin
As result of no response i will try again and add some more information
for you.
The given problem is the same. I have many DB's which have for unknown
reason, differences in Filesizes, if you check them with "du" or "ls",
in their Filenodes.
To get a little deeper, I have around 300 Postgres 9.0 databases. The
databases which get affected of this issue got all replicated via
streaming replication to new hardware, they are all insside a vm. The
new hardware is the same like the old, but differs with Kernel.
Old: 2.6.39 New: 3.1.4
One Example:
###
/var/lib/postgresql/9.0/main/base/43169# ls -lh 64121
-rw------- 1 postgres postgres 58M 2012-02-16 17:03 64121
/var/lib/postgresql/9.0/main/base/43169# du -sh 64121
89M 64121
###
So this file "64121" has a difference of 31MB.
To get some informations of this file I played a little bit with XFS tools.
###
/var/lib/postgresql/9.0/main/base/43169# xfs_bmap 64121
64121:
0: [0..116991]: 17328672..17445663
/var/lib/postgresql/9.0/main/base/43169# xfs_fsr -v 64121
64121
64121 already fully defragmented.
/var/lib/postgresql/9.0/main/base/43169# xfs_info /dev/xvda1
meta-data=/dev/root isize=256 agcount=4, agsize=959932 blks
= sectsz=512 attr=2
data = bsize=4096 blocks=3839727, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096
log =internal bsize=4096 blocks=2560, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
/var/lib/postgresql/9.0/main/base/43169# cat /proc/mounts
rootfs / rootfs rw 0 0
/dev/root / xfs rw,noatime,nodiratime,attr2,delaylog,nobarrier,noquota 0 0
tmpfs /lib/init/rw tmpfs rw,nosuid,relatime,mode=755 0 0
proc /proc proc rw,nosuid,nodev,noexec,relatime 0 0
sysfs /sys sysfs rw,nosuid,nodev,noexec,relatime 0 0
tmpfs /dev/shm tmpfs rw,nosuid,nodev,relatime 0 0
devpts /dev/pts devpts
rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000 0 0
###
Strange, or not? Regarding this informations, the file is contiguous on
disk and has of course no fragmentation, so why is it showing so much
diskusage?
The relation this filenode is belonging to, is an index, and regarding
my last overview it seems that this happens for 95% only to indexes/pkeys.
Well you could think i have some strange config settings, but we
distribute this config via puppet, and also the servers on old hardware
have this config. so things like fillfactor couldn't explain this.
We also thought that there could be some filehandles still exist. So we
decided to reboot. Wow, we thought we got it, the free diskspace
increased slowly for a while. But then, after 1-2GB captured diskspace
it went back to normal and the filenodes grew again. This doesn't
explain it as well. :/
One more thing, a xfs_fsr /dev/xvda1 recaptures also some diskspace, but
with same effect as a reboot.
For now the only things which are really different are the
kernelversions. // i now tried to reboot them with the 2.6.39 kernel,
but getting the same behavior like with the 3.1.4 kernel.
If you have _any_ idea about what could cause this behavior, please tell
me. i'm getting out of ideas.
Thanks a lot.
regards
Bernhard
On 02/14/2012 02:22 PM, Bernhard Schrader wrote:
> Hi all,
>
> Problem:
> If I use
> SELECT pg_size_pretty(pg_database_size('dbname')) As fulldbsize;
>
> fulldbsize
> ------------
> 6455 MB
> (1 row)
>
> If I compare this output with
> /var/lib/postgresql/9.0/main/base/[DBFOLDER]
> I have a difference of 3 GB, which I think is not normal.
>
> To make a little bit clearer what i mean:
>
> /var/lib/postgresql/9.0/main/base/43169# du --apparent-size -h
> 6.4G .
>
> /var/lib/postgresql/9.0/main/base/43169# du -sh
> 9.4G .
>
> Is such a big fragmentation a normal behavior? It's splitted to several
> Filenodes.
>
> I also made a "xfs_fsr" to defrag all of this, i gathered around 1 GB
> back ( would be more if the tables wouldn't be written in this time )
> But within some hours the fragmentation was back..
>
> There is also no big dead tuple count in this database, it's getting a
> vacuum analyze every night.
>
> Right now i am out of ideas... What do you think i could do?
> If you need more information i can provide.
>
> Environment:
> - OS: Debian Lenny
> - Disksize: 15GB
> - Filesystem: XFS
> - Psql: 9.0.3
>
> thanks in advance.
>
> regards
> Bernhard
>
>
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Big difference in databasesize compared with disksize
@ 2012-02-17 18:00 Steve Crawford <scrawford@pinpointresearch.com>
parent: Bernhard Schrader <bernhard.schrader@innogames.de>
0 siblings, 0 replies; 3+ messages in thread
From: Steve Crawford @ 2012-02-17 18:00 UTC (permalink / raw)
To: Bernhard Schrader <bernhard.schrader@innogames.de>; +Cc: pgsql-admin
On 02/17/2012 01:57 AM, Bernhard Schrader wrote:
> As result of no response i will try again and add some more
> information for you.
>
> The given problem is the same. I have many DB's which have for unknown
> reason, differences in Filesizes, if you check them with "du" or "ls",
> in their Filenodes.
Since you are getting different results from the OS tools (ls, du) on an
XFS system I'd check for info on XFS lists.
Googling "xfs du ls size difference" gives about 95,000 pages related to
this issue.
Cheers,
Steve
^ permalink raw reply [nested|flat] 3+ messages in thread
end of thread, other threads:[~2012-02-17 18:00 UTC | newest]
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2012-02-14 13:22 Big difference in databasesize compared with disksize Bernhard Schrader <bernhard.schrader@innogames.de>
2012-02-17 09:57 ` Bernhard Schrader <bernhard.schrader@innogames.de>
2012-02-17 18:00 ` Steve Crawford <scrawford@pinpointresearch.com>
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