Hitting index for multi-db query

On Fri, Oct 2, 2015 at 11:55 PM, Marco Lettere <marco.lettere at dedalus.eu> wrote: > Hello all, > > I have to query all the databases on one server for docs matching a query. > > I do it with this query for example: > > > db:list() ! db: open(.)/entry[@about='abc'] > > > This query never hits the available attribute index. > > I could rewrite the query to something like > > > db:list() ! attribute(., 'abc', 'about')/.. > > > and in this case it takes advantage of the index of course. > > The problem is that I have to implement more queries which have much more > generic predicate structures where I probably won't be able to use indexes > explicitly. > > Is there any possibility to rewrite this query in order to use the indexes > implicitly? > > Thanks, > > Marco.

From: Christian Grün <christian.gruen at gmail.com> Sent: Saturday, October 3, 2015 10:27 AM To: Marco Lettere Cc: BaseX Subject: Re: [basex-talk] Hitting index for multi-db query Hi Marco Sorry, not at the moment. To trigger our index optimizations, the addressed database must be opened at compile time. Maybe we could introduce pragma expressions or a new global option that enforces index access whenever possible, but it's getting tricky as soon as a query may be optimizable in different ways (an example /a[@b = 'c']/d[text() ='e']). I'll have some more thoughts. If you have some suggestions on how a good extension could look like, your feedback is welcome! Christian On Fri, Oct 2, 2015 at 11:55 PM, Marco Lettere <marco.lettere at dedalus.eu> wrote: > Hello all, > > I have to query all the databases on one server for docs matching a query. > > I do it with this query for example: > > > db:list() ! db: open(.)/entry[@about='abc'] > > > This query never hits the available attribute index. > > I could rewrite the query to something like > > > db:list() ! attribute(., 'abc', 'about')/.. > > > and in this case it takes advantage of the index of course. > > The problem is that I have to implement more queries which have much more > generic predicate structures where I probably won't be able to use indexes > explicitly. > > Is there any possibility to rewrite this query in order to use the indexes > implicitly? > > Thanks, > > Marco.

> Would I possibly solve the issue by importing an .xqm file that I generate offline with all the database names?

> Maybe one could think of recognizing somehow that a query wants to query ALL the available databases and this should be equivalent of knowing the database names at compile time. > Don't have any other clue ... > Bye, M. > > ________________________________________ > From: Christian Grün <christian.gruen at gmail.com> > Sent: Saturday, October 3, 2015 10:27 AM > To: Marco Lettere > Cc: BaseX > Subject: Re: [basex-talk] Hitting index for multi-db query > > Hi Marco > > Sorry, not at the moment. To trigger our index optimizations, the > addressed database must be opened at compile time. > > Maybe we could introduce pragma expressions or a new global option > that enforces index access whenever possible, but it's getting tricky > as soon as a query may be optimizable in different ways (an example > /a[@b = 'c']/d[text() ='e']). I'll have some more thoughts. If you > have some suggestions on how a good extension could look like, your > feedback is welcome! > > Christian > > > On Fri, Oct 2, 2015 at 11:55 PM, Marco Lettere <marco.lettere at dedalus.eu> wrote: >> Hello all, >> >> I have to query all the databases on one server for docs matching a query. >> >> I do it with this query for example: >> >> >> db:list() ! db: open(.)/entry[@about='abc'] >> >> >> This query never hits the available attribute index. >> >> I could rewrite the query to something like >> >> >> db:list() ! attribute(., 'abc', 'about')/.. >> >> >> and in this case it takes advantage of the index of course. >> >> The problem is that I have to implement more queries which have much more >> generic predicate structures where I probably won't be able to use indexes >> explicitly. >> >> Is there any possibility to rewrite this query in order to use the indexes >> implicitly? >> >> Thanks, >> >> Marco.