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NUM_IOSERVERS=AUTOMATIC behaviour is changed from 10.5FP7

Question & Answer


Question

After updating to 10.5FP7 from an older fixpack level, I noticed that AUTOMATIC value for NUM_IOSERVERS is changed even though any settings are not changed. Is it expected bahavior?

Answer

Yes, it is expected. Due to IT09990, we changed the fomula for calculating the number of prefetchers to start at database activation time.
Until 10.5FP6, we use following fomula:
number of prefetchers =
  max( max( max over all table spaces( parallelism setting ),
    number of cores * number of SMT threads ), 16 )

Starting from 10.5FP7, we use following fomula:
number of prefetchers =
  max( max( max over all table spaces( parallelism setting ),
    number of cores * number of SMT threads ), 12 )

So you can see the following output in 10.5FP6 and FP7:

FP6:
$ db2 get db cfg | grep NUM_IOSERVERS
Number of I/O servers                   (NUM_IOSERVERS) = AUTOMATIC(16)

FP7
$ db2 get db cfg | grep NUM_IOSERVERS
Number of I/O servers                   (NUM_IOSERVERS) = AUTOMATIC(12)

[{"Product":{"code":"SSEPGG","label":"Db2 for Linux, UNIX and Windows"},"Business Unit":{"code":"BU058","label":"IBM Infrastructure w\/TPS"},"Component":"Database Objects\/Config - Bufferpools","Platform":[{"code":"PF002","label":"AIX"},{"code":"PF010","label":"HP-UX"},{"code":"PF016","label":"Linux"},{"code":"PF027","label":"Solaris"},{"code":"PF033","label":"Windows"}],"Version":"10.5","Edition":"","Line of Business":{"code":"LOB10","label":"Data and AI"}}]

Document Information

Modified date:
16 June 2018

UID

swg21991890

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