Re: Cache for query plans

Roberto Abalde wrote:
> Hi,
>
> I need to implement a cache for query plans as part of my BSc thesis. Does
> anybody know what happened to Karel Zak's patch?
   Dunno.

> I'm also looking for some comments & tips about how to implement a cache for
> query plans and how to deal with the implementation of shared memory in
> PSQL.
   Query  trees and -plans are only handled on the backend side.   And don't forget that dealing with such thing on
the client   side,  which allmost runs under clients memory control, opens   a can of worms with respect to  security
and other  issues.   Plus  it's not a psql only thing. If you want applications to   benefit from it, it has to be
implementedon the libpq level.
 
   That said, general purpose query cacheing using shared memory   must at least run the parser on each query string.
It could   then  build  some  hash  key  based  on  the  querytree  node   structure and hold query trees and -plans in
shared  memory.   If  it  finds  a query with the same key in it's cache, it'll   take a closer look if the cached and
actualquery only differ   in const nodes and instead of planning/optimizing again it'll   just use the cached one. A
queryshouldn't make it  into  the   cache  just at first occurence, but it's hash key does and is   subsequently
countedup. Combined with some  ageing  and  the   rest of required herbs it'll serve a good meal for some types   of
applications. Thus,  it  has  to  be  a   per   database   configurable feature.
 
   Explicit PREPARE and EXECUTE statements (or whatever keywords   actually used) are IMHO better candidates for a  per
session   (backend)   non-shared   implementation,  because  how  could   another client be sure that a given query
identifieractually   does  or  doesn't  exist  and  what  querystring is/should be   associated with it?
 

> Greetings,
> Roberto
>
> PS: Sorry for my english :(
   What's wrong with it?


Jan

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