IDS Forum

Re: Informix nonblocking checkpoints slow

Posted By: Art Kagel
Date: Thursday, 12 January 2012, at 11:59 a.m.

In Response To: Re: Informix nonblocking checkpoints slow (NATYURAL HORACIO)

Horatio:

OK, so, I reformatted some of the output below so I can read it better. It
looks like over 95% of the checkpoint time is being spend on disk
flushing. Note that always the number of checkpoint waits is usually zero
and not greater than 23 and that the average block time is less then 1/10
of a second. I believe that the performance problems you are seeing are a
side effect of the high IO during the checkpoints when, typically, between
10,000 and 50,000 dirty pages have to be flushed to disk. It is the IO
activity due to these flushes that is slowing down read activity required
to service your other active sessions during the checkpoint, not the
checkpoint itself.

There are several possible causes and several possible ways to ameliorate
the problem and to ultimately resolve it. If you do not have the technical
System Administration and Storage Administration staff available to help
you do that I suggest that you get outside help. I can offer the services
of Advanced DataTools Corp. if you want to contact me or our offices
directly. Beyond that I would suggest that you get help. There may be OS
problems, storage array problems, server tuning problems, IO channel
problems, network problems any and all of which may be causing this. Here
are some general suggestions:

- More buffers will reduce the load on the IO subsystems during checkpoints
be making more data available in memory.
- Reducing the checkpoint interval may reduce the amount of IO at each
checkpoint but that may just exacerbate the IO problems if this is actually
related to slow write IO.
- You can try decreasing the lru_min_dirty and lru_max_dirty values for
your buffer caches which will reduce the amount of dirty pages that need to
be flushed out at checkpoint time.

If these suggestions do not help, then more extensive analysis of the
problem is required to determine the root cause and to find solutions.

Art

Art S. Kagel
Advanced DataTools (www.advancedatatools.com)
Blog: http://informix-myview.blogspot.com/

Disclaimer: Please keep in mind that my own opinions are my own opinions
and do not reflect on my employer, Advanced DataTools, the IIUG, nor any
other organization with which I am associated either explicitly,
implicitly, or by inference. Neither do those opinions reflect those of
other individuals affiliated with any entity with which I am affiliated nor
those of the entities themselves.

On Thu, Jan 12, 2012 at 8:43 AM, NATYURAL HORACIO <
horacio.natyural@gmail.com> wrote:

> here it is, oddly the dskflu/sec are really low. checkpoints are long when
> the
> dsk flu/seconds are high.
>
> Critical Sections Physical Log Logical Log
>
> Clock Total Flush Block # Ckpt Wait
> Long # Dirty Dskflu Total Avg Total Avg
> Interval Time Trigger LSN Time Time Time Waits Time
> Time Time Buffers /Sec Pages /Sec Pages /Sec
> 387978 14:20:17 CKPTINTVL 1153313:0x4a0a0bc 125.3 125.0 0.0 10 0.1 0.1
> 0.2 13323 106 7149 23 19240 63
> 387979 14:26:24 CKPTINTVL 1153313:0x9e9c2a0 187.2 180.1 0.0 123 7.0 3.3
> 7.1 16321 90 10757 34 26726 85
> 387980 14:30:04 CKPTINTVL 1153313:0xe380018 100.0 99.9 0.0 2 0.0 0.1
> 0.1 15631 156 8314 27 25301 84
> 387981 14:37:34 CKPTINTVL 1153314:0x68073b8 240.8 239.6 0.0 13 0.3 0.8
> 1.2 16993 70 11837 38 47907 154
> 387982 14:42:17 CKPTINTVL 1153314:0xc91b750 193.0 190.4 0.0 97 2.4 1.4 2.6
> 16987 89 9631 29 28383 85
> 387983 14:45:09 CKPTINTVL 1153315:0x58d2a4 52.3 52.0 0.0 21 0.1 0.1 0.4
> 10312
> 198 5349 17 14800 47
> 387984 14:52:17 CKPTINTVL 1153315:0x687e654 158.8 156.2 0.0 17 0.3 1.5 2.6
> 18160 116 12074 37 35648 110
> 387985 14:57:37 CKPTINTVL 1153315:0xbe970b4 170.5 170.3 0.0 4 0.0 0.2 0.2
> 17055 100 9795 32 35193 115
> 387986 15:03:47 CKPTINTVL 1153316:0x3851180 220.4 189.3 0.0 372 30.9 12.3
> 30.8
> 16335 86 10037 28 28886 82
> 387987 15:07:09 CKPTINTVL 1153316:0x755a0bc 83.0 82.6 0.0 7 0.0 0.3 0.3
> 16281
> 197 8188 26 20897 67
> 387988 15:13:49 CKPTINTVL 1153316:0xdbf63b0 158.2 157.9 0.0 13 0.1 0.2 0.3
> 16160 102 11392 35 33779 104
> 387989 15:18:48 CKPTINTVL 1153317:0x3c2442c 149.4 147.8 0.0 28 0.5 1.0 1.6
> 15788 106 9297 30 23258 75
> 387990 15:22:05 CKPTINTVL 1153317:0x86d4048 17.2 17.1 0.0 5 0.0 0.1 0.1
> 16925
> 987 9848 30 20380 62
> 387991 15:27:18 CKPTINTVL 1153318:0x5ae11d0 14.0 13.7 0.0 6 0.0 0.2 0.2
> 16785
> 1222 19510 61 50050 157
> 387992 15:32:30 CKPTINTVL 1153318:0xe194068 12.8 12.7 0.0 7 0.0 0.1 0.1
> 16478
> 1299 14081 44 35540 113
> 387993 15:37:42 CKPTINTVL 1153319:0x79530bc 12.6 12.2 0.0 12 0.1 0.2 0.3
> 16599
> 1356 12728 40 34188 109
> 387994 15:43:00 CKPTINTVL 1153319:0xd15713c 18.2 17.7 0.0 18 0.2 0.3 0.4
> 16624
> 936 8120 26 22847 73
> 387995 15:48:12 CKPTINTVL 1153320:0x1cc11b0 12.8 12.4 0.0 11 0.2 0.3 0.4
> 16736
> 1344 6786 21 14690 46
> 387996 15:53:25 CKPTINTVL 1153320:0x91eb3e8 14.0 13.7 0.0 13 0.0 0.2 0.3
> 16543
> 1208 14065 45 30922 99
> 387997 15:58:39 CKPTINTVL 1153320:0xe9ec5cc 14.7 14.4 0.0 8 0.0 0.2 0.2
> 16837
> 1165 10719 34 23309 74
>
>
>
> *******************************************************************************
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>
>

--e89a8f3bb03931add404b657ac00

Messages In This Thread

• Informix nonblocking checkpoints slow
  NATYURAL HORACIO -- Wednesday, 11 January 2012, at 10:48 a.m.
  • Re: Informix nonblocking checkpoints slow
    Art Kagel -- Wednesday, 11 January 2012, at 11:26 a.m.
    • Re: Informix nonblocking checkpoints slow
      NATYURAL HORACIO -- Thursday, 12 January 2012, at 8:43 a.m.
      • Re: Informix nonblocking checkpoints slow
        Art Kagel -- Thursday, 12 January 2012, at 11:59 a.m.
        • Re: Informix nonblocking checkpoints slow
          NATYURAL HORACIO -- Thursday, 12 January 2012, at 12:16 p.m.
  • Re: Informix nonblocking checkpoints slow
    Fernando Nunes -- Wednesday, 11 January 2012, at 1:31 p.m.
  • Re: Informix nonblocking checkpoints slow
    Spokey Wheeler Gmail -- Thursday, 12 January 2012, at 12:58 a.m.

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