Re: [HACKERS] Cache query (PREPARE/EXECUTE)

> "Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
> > I think so.  The problem is that Node struct couldn't be freed safely
> > due to the lack of reference count in its definition.  As far as I see
> > plans could be destroyed only when the memory context in which
> > they are placed are destroyed.
>
> This is overly conservative.  It should be safe to destroy a plan tree
> via freeObject() if it was created via copyObject() --- and that is
> certainly how the plan would get into a permanent memory context.
>
> Currently, rule definitions are leaked in CacheContext at relcache
> flushes.  I plan to start freeing them via freeObject at the beginning
> of the 7.1 development cycle --- I didn't want to risk it during the
> runup to 7.0, but I believe it will work fine.
   I  don't  see  any  reason,  why  each  saved  plan  or  rule   definition  shouldn't  go  into  it's  own,  private
 memory   context.  Then,  a  simple  destruction of the entire context   will surely free all it's memory, and I think
itwill also be   faster  since  the  en-block  allocation, done for many small   objects, doesn't need to free all them
separately- it throws   away  the  entire  blocks. No need to traverse the node tree,   nor any problems with multiple
objectreferences  inside  the   tree.
 
   Since  plans  are (ought to be) saved via SPI_saveplan(plan),   there is already a central point where it  can  be
done for   plans.  And a corresponding SPI_freeplan(savedplan) should be   easy to create, since the context can be
heldin the SPI plan   structure itself.
 
   Needs  only  some  general naming convention for these memory   contexts.  But something like a
       MemoryContext CreateObjectMemoryContext();
   that  guarantees  uniqueness  in  the  context  name  and  no   conflicts  by using some appropriate prefix in them
shoulddo   it.
 
   The overhead, payed for separate contexts is IMHO negligible.


Jan

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