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IT37242: WITH DBSPACES COMPRISED OF MANY CHUNKS, FREQUENT 'CHUNK DOWN' CHECKING CAN BE VERY EXPENSIVE

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APAR status

  • Closed as program error.

Error description

  • On a secondary server system having multiple dbspaces with a
    couple hundreds of chunks each, a significant log apply slowness
    can be observed during heavy load on primary that, esp. with
    HDR, can affect primary performance too.
    
    Here's how this looks in 'onstat -g laq':
    
    Log Apply Info:
    Thread         Queue    Total      Avg
                    Size   Queued    Depth
    wreplay_1           0   189676     1.35
    wreplay_2           0   153139     1.34
    wreplay_3           0   260041     1.48
    wreplay_4           0   161107     1.32
    wreplay_5           0   164985     1.33
    wreplay_6           0   115743     1.17
    wreplay_7           0   246979     0.42
    wreplay_8           0   172274     1.36
    wreplay_9           0   125461     1.29
    wreplay_10          0   116958     1.20
    wreplay_11          0   211963     1.64
    
    Secondary Apply Queue:         Total Buffers:48 Size:2048K Free
    Buffers:0
    Log Recovery Queue:            Total Buffers:48 Size:20480K Free
    Buffers:0
    Log Page Queue:                Total Buffers:1024 Size:2K Free
    Buffers:0
    Log Record Queue:              Total Buffers:1000 Size:16K Free
    Buffers:981
    
    
    So worker threads' queues empty or nearly empty most of the time
    while Secondary Apply Queue, Log Recovery Queue and Log Page
    Queue completely full, yet Log Record Queue again hardly used,
    indicating a bottleneck at extracting log records from log pages
    which is the bld_logrecs thread's business.
    
    Looking at bld_logrecs thread under such conditions, that thread
    would appear 'running' most of the time.
    

Local fix

Problem summary

  • ****************************************************************
    * USERS AFFECTED:                                              *
    * Users of Informix Server prior to 12.10.xC15 and 14.10.xC7.  *
    ****************************************************************
    * PROBLEM DESCRIPTION:                                         *
    * See Error Description                                        *
    ****************************************************************
    * RECOMMENDATION:                                              *
    * Upgrade to Informix Server 12.10.xC15 or 14.10.xC7 (when     *
    * available).                                                  *
    ****************************************************************
    

Problem conclusion

  • Fixed in Informix Server 12.10.xC15 and 14.10.xC7.
    

Temporary fix

Comments

APAR Information

  • APAR number

    IT37242

  • Reported component name

    INFORMIX SERVER

  • Reported component ID

    5725A3900

  • Reported release

    C10

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2021-06-14

  • Closed date

    2021-08-31

  • Last modified date

    2021-08-31

  • APAR is sysrouted FROM one or more of the following:

  • APAR is sysrouted TO one or more of the following:

Fix information

  • Fixed component name

    INFORMIX SERVER

  • Fixed component ID

    5725A3900

Applicable component levels

[{"Line of Business":{"code":"LOB10","label":"Data and AI"},"Business Unit":{"code":"BU053","label":"Cloud & Data Platform"},"Product":{"code":"SSGU8G","label":"Informix Servers"},"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"C10"}]

Document Information

Modified date:
01 September 2021