Re: [hibernate-dev] Reducing the memory usage of HQLQueryPlan

I'd like to note that with the array rendering strategy i.e. `where x = ANY(?)` and the padding strategy i.e. pad the JDBC params, we can reduce the cache trashing and avoid re-walking of the SQL-AST. IMO it's not necessary to keep the SQL-AST around for the purpose of parameter expansion, but maybe there are other reasons to keep it around? Wdyt? Mit freundlichen Grüßen, ------------------------------------------------------------------------ *Christian Beikov* Am 09.08.2018 um 16:57 schrieb Steve Ebersole: > In 6.0 HQLQueryPlan is replaced by AggregatedSelectQueryPlanImpl[1] > (polymorphic queries) and ConcreteSqmSelectQueryPlan[2]. > > ConcreteSqmSelectQueryPlan holds a reference to the SQM AST; > AggregatedSelectQueryPlanImpl > hold 2+ ConcreteSqmSelectQueryPlans. AggregatedSelectQueryPlan operates > much like HQLQueryPlan when holding more than one QueryTranslator. > > ConcreteSqmSelectQueryPlan ought to hold much less state (and hence use > less memory) than QueryTranslator. And it follows that > AggregatedSelectQueryPlan > ought to consume less memory than HQLQueryPlan+QueryTranslators. > > The other win, which is likely much bigger gain, is that previously > parameter expansions (think `... where x in (:someListOfValues)`) resulted > in separate plans based on the number of values in `someListOfValues` - > more HQLQueryPlan instances for the same HQL. This is actually one of the > (many) explicit design goals for 6. The cached plan is the same regardless > of the number of values in `someListOfValues`; the expansion happens during > execution. > > Relatedly, this last part also lets us reuse cached plans in more scenarios > than we do currently: enabled Filters, enabled FetchProfiles, etc. All of > these things are applied/resolved during execution. So there is a slight > trade off between reducing the number of cached plans versus translating > the SQM AST to a SQL AST. This is important too because often times the > query plan cache is "overrun" due to all of the "different cache keys" > aspect (parameter list expansion, filters, etc) - so that often the queries > get pushed from the cache and need complete re-building. > > We cannot really verify this though until Luis, et.al, are able to resume > the performance testing... > > [1] > https://github.com/sebersole/hibernate-core/blob/wip/6.0/hibernate-core/s... > [2] > https://github.com/sebersole/hibernate-core/blob/wip/6.0/hibernate-core/s... > > > On Thu, Aug 9, 2018 at 9:21 AM Guillaume Smet <guillaume.smet(a)gmail.com&gt; > wrote: > >> Hi, >> >> >From what I can see, the HQLQueryPlan objects are rather big, mostly due >> to >> the sqlAst element of the QueryTranslators. >> >> They can consume a fair amount of memory when you have a lot of HQL >> queries. >> >> We need at least some of the information collected by the AST but I'm >> wondering if we really need to keep all the AST information in memory once >> the query has been parsed and the SQL query generated. >> >> The purpose of this email is mostly to know if this element has been >> accounted for in 6 development? >> >> I haven't checked if it would be doable to improve the situation without >> breaking too much stuff in 5.x. >> >> Thanks. >> >> -- >> Guillaume >> _______________________________________________ >> hibernate-dev mailing list >> hibernate-dev(a)lists.jboss.org >> https://lists.jboss.org/mailman/listinfo/hibernate-dev >> > _______________________________________________ > hibernate-dev mailing list > hibernate-dev(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/hibernate-dev _______________________________________________ hibernate-dev mailing list hibernate-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev