For the quick and dirty workaround I would adjust the blevel on the
partition and at the table level. Any time anything triggers a stats
collection on the table you MIGHT find that the blevel would be
recalculated, but if you've set the blevel on the partition to 2 then the
problem could only re-appear if the stats on that partition were
re-collected (and the collection was set to cascade to the indexes). This
happens because the global (table level) blevel is set to be the maximum of
the partition blevel values (See:
https://jonathanlewis.wordpress.com/2010/11/14/local-indexes-2/ ;)
Given this behaviour it would probably be sensible at some point to split
the over-large partition into two pieces so that an unexpected stats gather
won't accidentally re-introduced the higher blevel).
Regards
Jonathan Lewis
On Tue, 22 Jun 2021 at 06:20, Lok P <loknath.73@xxxxxxxxx> wrote:
Thanks a lot.
In regards to get/set_index_stats, I am thinking of the stats
gathering(which I believe is currently happening in an INCREMENTAL way)
which has turned the blevel at global level to -3 because of that one
partition mess. So if i forcibly set the BLEVEL for the 15th jun index
partition to -2 manually(whose value is currently-3) using set_index_stats,
will the subsequent stats gather revert the BLEVEL of the index at global
level i.e. in dba_indexes automatically to -2?
Or it will do the opposite, i.e. it will regather the stats on that 15th
jun index partition and make it -3 along with global blevel to -3?
Or are you pointing towards forcibly get/set_index_stats the blevel
to-2 for both local i.e the 15th jun partition along with global blevel for
that index?
Regards
Lok
On Tue, Jun 22, 2021 at 12:50 AM Jonathan Lewis <jlewisoracle@xxxxxxxxx>
wrote:
You might get away with two calls to dbms_stats, one to "get_index_stats"
the other to "set_index_stats". modifying the variable holding the blevel
between the calls.
Example here: https://jonathanlewis.wordpress.com/2010/01/06/copy-stats/
As far as the split partition is concerned - if the 15th June is now in a
read-only stats you could do the following steps (to hide the time, rather
than getting rid of it).
create table temp14 as select * from15th June partition where data = 14th
june, create indexes
create table temp15 as select * from15th June partition where data = 15th
june, create indexes
truncate 15th June partition
split partition into 14th june and 15th june
exchange partition for 14th june and temp14 including indexes
exchange partition for 15th june and temp15 including indexes
The users would only see brief interruptions on the exchange - unless you
had some global indexes to maintain as well.
Regards
Jonathan Lewis
On Mon, 21 Jun 2021 at 19:55, Lok P <loknath.73@xxxxxxxxx> wrote:
Hi All, It's version 11.2.0.4 of Oracle.
We are having a situation in which multiple queries suddenly changed the
execution path and deviated from the local indexed access path to the FTS
path(partition range all) for a daily range partitioned table. And then
after debugging into the issue we found that the COST of the index access
actually has been increased because of the increase in BLEVEL of the index.
And the BLEVEL has been increased from 2 to 3 in global level(dba_indexes)
because of one of the missing daily partitions. For e.g. 14th jun partition
was missing , so 15th jun partition now holds both 14th june and 15th jun
data, so its twice as bigger as a normal daily partition.
The missing day range partition caused the subsequent day partitions to
actually hold two partitions/days worth of data and thus the blevel of that
specific local index increased from 2 to -3 for that index partition. and
since then, in global level(dba_indexes) the blevel is staying as-3 for
that index, costing that index access higher and thus making plan change
for many queries.
My question is how should we handle such a situation ? Should we go back
and break the specific partition(15th Jun partition) into two daily range
partitions i.e. 14th and 15th (which i believe is going to take lot of time
and resources considering this table has ~8 different local indexes in it)
and gather stats again or is there any other way to just tweak the stats
for that one big partition such that the global index BLEVEl can be back to
-2 , and get this issue fixed?
Regards
Lok
