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Problem IT11260
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Status: Closed |
UNCLEAR AND FAULTY DEPENDENCY OF NON-PDQ QUERY PLAN ON DS_TOTAL_MEMORY / DS_MAX_QUERIES
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| product: |
INFORMIX SERVER / 5725A3900 / B70 - IDS 11.70 |
| Problem description: |
It comes somewhat by surprise that the query plan optimizer
decision of non-PDQ queries also can have a dependency on
DS_TOTAL_MEMORY / DS_MAX_QUERIES, i.e. the configured MGM
quantum. In this particular case the query would decide for a
sequential scan instead of indexed access path and cause a
sub-second execution to change to many minutes, when less than
some 3700KB quantum are configured.
What's even worse is that the involved memory calculation seems
to be flawed in a way that really large DS_TOTAL_MEMORY
configurations suddenly can fall into 'low memory' mode as well,
depending on the DS_MAX_QUERIES setting, so probably with a good
deal of accident involved.
There also seems to be a dependency on data distributions as
this happens to a query that behaved well over a long time, then
suddenly started choosing the bad plan after update statistics
was run - with no other system changes (wrt. DS configuration). |
| Problem Summary: |
****************************************************************
* USERS AFFECTED: *
* All users *
****************************************************************
* PROBLEM DESCRIPTION: *
* See Error Description *
****************************************************************
* RECOMMENDATION: *
* Update to IBM Informix Server 11.70.xC9 *
**************************************************************** |
| Local Fix: |
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| Solution |
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| Workaround |
not known / see Local fix |
| Timestamps |
Date - problem reported :
Date - problem closed :
Date - last modified :
| 16.09.2015
09.06.2017
09.06.2017 |
| Problem solved at the following versions (IBM BugInfos) |
11.70.xC9
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| Problem solved according to the fixlist(s) of the following version(s) |
