Re: About method of PostgreSQL's Optimizer

Thank's guys!
I'll send to pgsql-hackers...

[]'s
Pryscila

On 9/13/05, Neil Conway <neilc(at)samurai(dot)com> wrote:
>
> Pryscila B Guttoski wrote:
> > On my master course, I'm studying the PostgreSQL's optimizer.
> > I don't know if anyone in this list have been participated from the
> > PostgreSQL's Optimizer development, but maybe someone can help me on
> this
> > question.
>
> pgsql-hackers might be more appropriate.
>
> > PostgreSQL generates all possible plans of executing the query (using an
> > almost exhaustive search), then gives a cost to each plan and finally
> the
> > cheapest one is selected for execution.
> > There are other methods for query optimization, one of them is based on
> plan
> > transformations (for example, using A-Star algorithm) instead of plan
> > constructions used by PostgreSQL.
>
> Right, the main query planner uses a nearly-exhaustive search. For
> queries with many joins (when the cost of an exhaustive search would be
> prohibitive), "GEQO" is used, which uses a genetic algorithm to avoid an
> exhaustive search of the solution space.
>
> > Does anyone know why this method was choosen?
>
> As far as I know, the main planner algorithm is fairly standard and is
> mainly different from System R's canonical algorithm in the details,
> like whether non-left-deep plans are pruned.
>
> > Are there any papers or researches about it?
>
> There are many papers on the System R algorithm and similar techniques,
> which should explain the basic motivations for the design. I'm not aware
> of any papers specifically on the PostgreSQL query optimizer, although
> there have been a few presentations on it:
>
> http://neilc.treehou.se/optimizer.pdf
> http://conferences.oreillynet.com/presentations/os2003/lane_tom.pdf
>
> -Neil
>