default for oracle 7.x with respect to optimizer_mode

default for oracle 7.x with respect to optimizer_mode

Post by Jeff Kis » Sun, 31 Dec 1899 09:00:00



Can someone tell me where to find (I looked the docs over, honest)
what the default is for Oracle 7.x as far as optimizer_mode ?
I believe you can put a number of parameters in the initorcl.ora file
to set this, but I don't know what the system does if the parameter is
missing.

Oracle 8, I found out, defaults to "optimizer_mode=choose", unless
statitistics are not available. In that case it uses rule-based
instead.

Thanks
Jeff Kish


 
 
 

default for oracle 7.x with respect to optimizer_mode

Post by Mike Mountjo » Sun, 31 Dec 1899 09:00:00


The default is RULES based mode in ORA 7 and CHOOSE in ORA 8

The database switches to CHOOSE mode when you issue the command

ANALYZE TABLE <table_name> COMPUTE STATISTICS.

Regrds,
Mike


> Can someone tell me where to find (I looked the docs over, honest)
> what the default is for Oracle 7.x as far as optimizer_mode ?
> I believe you can put a number of parameters in the initorcl.ora file
> to set this, but I don't know what the system does if the parameter is
> missing.

> Oracle 8, I found out, defaults to "optimizer_mode=choose", unless
> statitistics are not available. In that case it uses rule-based
> instead.

> Thanks
> Jeff Kish




 
 
 

default for oracle 7.x with respect to optimizer_mode

Post by MJEvan » Sun, 31 Dec 1899 09:00:00




> The default is RULES based mode in ORA 7 and CHOOSE in ORA 8
> The database switches to CHOOSE mode when you issue the command
> ANALYZE TABLE <table_name> COMPUTE STATISTICS.
> Regrds,
> Mike

Not exactly true, Mike.  It depends on which version of Oracle7.  For
7.3.4, the default is CHOOSE.  However, both 7.3.4 and 8 will use RULE
if you execute a query on a table that does not have statistics.  The
database will not automatically switch to CHOOSE if the optimizer_mode
is either set to RULE or has not been set (defaults to RULE) in an
earlier version than 7.3.4, no matter how many times you analyze the
tables.

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