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On the client protocol level: Can a query be executed multiple times?

Saturday, 23 February 2013 · 10 messages · last reply 26 Feb 2013
HH
Hans Hübner23 Feb 2013 21:41 #
I have a question regarding the client protocol: Can a query that has been prepared using the "QUERY" protocol message be executed only once, or multiple times? If it can be executed multiple times, with different parameter sets, how is the previous execution ended? The documentation of the "CLOSE" message seems to indicate the the query is unregistered when it is closed. Is there some documentation or sample code that illustrates the expected sequence of client messages for query execution? Thanks, Hans
CG
Christian Grün24 Feb 2013 20:29 #
Dear Hans,
Quoted text · Hans Hübner · 3 lines
> I have a question regarding the client protocol: Can a query that has been > prepared using the "QUERY" protocol message be executed only once, or > multiple times?
a query that is created with the client protocol can also be executed once. After running the query, you should get an exception saying "The query has already been executed.". The current approach shouldn’t represent any bottleneck, as query object are pretty light-weight objects. If your tests should yield unsatisfactory results, feel free to tell us more.
Quoted text · Hans Hübner · 2 lines
> Is there some documentation or sample code that illustrates the expected > sequence of client messages for query execution?
The example in our documentation refers to PHP, but it should be transferable to all other client APIs [1]. Best, Christian [1] http://docs.basex.org/wiki/Query_Mode
Quoted text · Hans Hübner · 15 lines
> On Sat, Feb 23, 2013 at 9:41 PM, Hans Hübner <hans.huebner at gmail.com> wrote: If it can be executed multiple times, with different > parameter sets, how is the previous execution ended? The documentation of > the "CLOSE" message seems to indicate the the query is unregistered when it > is closed. > > > Thanks, > Hans > > _______________________________________________ > BaseX-Talk mailing list > BaseX-Talk at mailman.uni-konstanz.de > https://mailman.uni-konstanz.de/mailman/listinfo/basex-talk >
HH
Hans Hübner24 Feb 2013 22:41 #
Hi Christian, thank you for getting back! On Sun, Feb 24, 2013 at 8:29 PM, Christian Grün <christian.gruen at gmail.com>wrote:
Quoted text · Christian Grün · 13 lines
> > I have a question regarding the client protocol: Can a query that has > been > > prepared using the "QUERY" protocol message be executed only once, or > > multiple times? > > a query that is created with the client protocol can also be executed > once. After running the query, you should get an exception saying "The > query has already been executed.". > > The current approach shouldn’t represent any bottleneck, as query > object are pretty light-weight objects. If your tests should yield > unsatisfactory results, feel free to tell us more. >
It is not that I'm really suffering from performance issues and I may well be in premature optimization land, but anyway: I am writing a web application which will be backed by a thin middleware implemented in Node.JS and BaseX as database. My performance interest is keeping the latency between the end user and the database at a minimum, and this basically means that I want to reduce the number of request-response interactions between the client, the middle layer and the database. Most of the queries will be stored in static files and parametrized by the incoming request. For example, I have a file named 'person.xq' in a special directory which is mapped to requests for /person/:id and looks like this:
declare variable $components := tokenize($path, '/');
declare variable $personId := $components[count($components)];
declare variable $person := /ballhaus/people/person[@id = $personId];

<person> {
  $person/(@*, *),
  <roles> {
    for $role in distinct-values(/ballhaus/events/event/people/person[@ref
= $personId]/@role)
    return <role name="{$role}"> {
      for $event in /ballhaus/events/event[people/person/@ref = $personId
and people/person/@role = $role]
      return <event ref="{$event/@id}">{$event/name}</event>
    } </role>
  } </roles>
} </person>
The middle layer reads this file, prepares the query using the "QUERY" client message, binds the "path" variable to the path of the request and then executes the query. The handler is not specific to the person query above, but works for all XQuery files in a designated directory. I am using a new Node.JS BaseX client that I wrote because I had this urge to pipeline things for minimum latency ( https://github.com/hanshuebner/simple-basex), and pipelining the BIND and EXECUTE together works fine (i.e. the middle layer does not need to wait for the confirmation for every BIND, and the protocol messages will be sent out together with the EXECUTE). Yet, the initial QUERY message needs to be synchronous in order to retrieve the query ID, and the query cannot be reused, so bound queries necessarily have more latency than simple COMMAND invocations. In other databases, the QUERY/BIND/EXECUTE thing is often referred to as prepared query execution, and prepared queries can usually be executed multiple times, which is why I asked. In the mean time, I have looked at the Java side of things a bit and found that for one, the behavior is as you describe, and for another, it would not be very hard to add a client interface for bound queries if that would really make sense. But then, maybe it would be even better to switch to the ReST interface instead. Anyway, all this is fun and exciting, and it is great to see that BaseX is supported well! Any thoughts about my approach would be grealy appreciated. Cheers, Hans
CG
Christian Grün25 Feb 2013 19:32 #
Hi Hans,
Quoted text · Hans Hübner · 1 line
> https://github.com/hanshuebner/simple-basex
thanks for the link; do you want us to add it to our Clients page [1]?
Quoted text · Hans Hübner · 3 lines
> In other databases, the QUERY/BIND/EXECUTE thing is often referred to as > prepared query execution, and prepared queries can usually be executed > multiple times, which is why I asked.
Yes, that’s an absolutely valid question/concern. As Francis pointed out, our current client API does not allow to rebind variables. This may change in the medium term as soon as XQuery expressions will be internally pre-compiled by BaseX. A simpler and short-term solution could be to cache the query string in our server-side QueryListener class and reparse it whenever necessary.
Quoted text · Hans Hübner · 2 lines
> But then, > maybe it would be even better to switch to the ReST interface instead.
Just as a hint: for our own, XQuery-based web applications, we have completely switched over to RESTXQ [2, 3]. Hope this helps, Christian [1] http://docs.basex.org/wiki/Clients [2] http://docs.basex.org/wiki/RESTXQ [3] http://files.basex.org/xmlprague2013/
Quoted text · Hans Hübner · 6 lines
> > Anyway, all this is fun and exciting, and it is great to see that BaseX is > supported well! Any thoughts about my approach would be grealy appreciated. > > Cheers, > Hans
HH
Hans Hübner25 Feb 2013 19:59 #
Hi Christian, On Mon, Feb 25, 2013 at 7:32 PM, Christian Grün <christian.gruen at gmail.com>wrote:
Quoted text · Christian Grün · 4 lines
> > https://github.com/hanshuebner/simple-basex > > thanks for the link; do you want us to add it to our Clients page [1]? >
I would not mind - The API is different from what the standard BaseX has, but I think it is rather easy to use. I may not use it much myself, though...
Quoted text · Christian Grün · 6 lines
> > But then, > > maybe it would be even better to switch to the ReST interface instead. > > Just as a hint: for our own, XQuery-based web applications, we have > completely switched over to RESTXQ [2, 3]. >
I think this is the route I'm going to follow, too. My requirements for the middle layer are rather moderate and can as well be fulfilled by some code that I write in Java instead. I basically wasted my weekend on coding up the new client, but it sure was fun. :) Cheers, Hans
CG
Christian Grün25 Feb 2013 23:40 #
Hi Hans, hi Francis, I decided to refactor our client query api a little: Variables and the context item can now be rebound, and a query can be run multiple times. Please note that the semantics of close() is the same as before: whenever a query is closed, it will completely be unregistered and is not available for new executions. Feedback is welcome, Christian
Quoted text · Hans Hübner · 33 lines
On Mon, Feb 25, 2013 at 7:59 PM, Hans Hübner <hans.huebner at gmail.com> wrote: > Hi Christian, > > > On Mon, Feb 25, 2013 at 7:32 PM, Christian Grün <christian.gruen at gmail.com> > wrote: >> >> > https://github.com/hanshuebner/simple-basex >> >> thanks for the link; do you want us to add it to our Clients page [1]? > > > I would not mind - The API is different from what the standard BaseX has, > but I think it is rather easy to use. I may not use it much myself, > though... > >> >> > But then, >> > maybe it would be even better to switch to the ReST interface instead. >> >> Just as a hint: for our own, XQuery-based web applications, we have >> completely switched over to RESTXQ [2, 3]. > > > I think this is the route I'm going to follow, too. My requirements for the > middle layer are rather moderate and can as well be fulfilled by some code > that I write in Java instead. > > I basically wasted my weekend on coding up the new client, but it sure was > fun. :) > > Cheers, > Hans
HH
Hans Hübner26 Feb 2013 08:39 #
Hi Christian, your changes work perfectly, thanks! I have updated the simple-basex client to support query preparation and multiple query execution: https://github.com/hanshuebner/simple-basex Cheers, Hans On Mon, Feb 25, 2013 at 11:40 PM, Christian Grün <christian.gruen at gmail.com>wrote:
Quoted text · Christian Grün · 51 lines
> Hi Hans, hi Francis, > > I decided to refactor our client query api a little: Variables and the > context item can now be rebound, and a query can be run multiple > times. Please note that the semantics of close() is the same as > before: whenever a query is closed, it will completely be unregistered > and is not available for new executions. > > Feedback is welcome, > Christian > ___________________________ > > On Mon, Feb 25, 2013 at 7:59 PM, Hans Hübner <hans.huebner at gmail.com> > wrote: > > Hi Christian, > > > > > > On Mon, Feb 25, 2013 at 7:32 PM, Christian Grün < > christian.gruen at gmail.com> > > wrote: > >> > >> > https://github.com/hanshuebner/simple-basex > >> > >> thanks for the link; do you want us to add it to our Clients page [1]? > > > > > > I would not mind - The API is different from what the standard BaseX has, > > but I think it is rather easy to use. I may not use it much myself, > > though... > > > >> > >> > But then, > >> > maybe it would be even better to switch to the ReST interface instead. > >> > >> Just as a hint: for our own, XQuery-based web applications, we have > >> completely switched over to RESTXQ [2, 3]. > > > > > > I think this is the route I'm going to follow, too. My requirements for > the > > middle layer are rather moderate and can as well be fulfilled by some > code > > that I write in Java instead. > > > > I basically wasted my weekend on coding up the new client, but it sure > was > > fun. :) > > > > Cheers, > > Hans >
CG
Christian Grün26 Feb 2013 08:49 #
…good to know. I’ve added you API in our Wiki [1]. Thanks, Christian [1] http://docs.basex.org/wiki/Clients
Quoted text · Hans Hübner · 68 lines
On Tue, Feb 26, 2013 at 8:39 AM, Hans Hübner <hans.huebner at gmail.com> wrote: > Hi Christian, > > your changes work perfectly, thanks! I have updated the simple-basex client > to support query preparation and multiple query execution: > https://github.com/hanshuebner/simple-basex > > Cheers, > Hans > > > On Mon, Feb 25, 2013 at 11:40 PM, Christian Grün <christian.gruen at gmail.com> > wrote: >> >> Hi Hans, hi Francis, >> >> I decided to refactor our client query api a little: Variables and the >> context item can now be rebound, and a query can be run multiple >> times. Please note that the semantics of close() is the same as >> before: whenever a query is closed, it will completely be unregistered >> and is not available for new executions. >> >> Feedback is welcome, >> Christian >> ___________________________ >> >> On Mon, Feb 25, 2013 at 7:59 PM, Hans Hübner <hans.huebner at gmail.com> >> wrote: >> > Hi Christian, >> > >> > >> > On Mon, Feb 25, 2013 at 7:32 PM, Christian Grün >> > <christian.gruen at gmail.com> >> > wrote: >> >> >> >> > https://github.com/hanshuebner/simple-basex >> >> >> >> thanks for the link; do you want us to add it to our Clients page [1]? >> > >> > >> > I would not mind - The API is different from what the standard BaseX >> > has, >> > but I think it is rather easy to use. I may not use it much myself, >> > though... >> > >> >> >> >> > But then, >> >> > maybe it would be even better to switch to the ReST interface >> >> > instead. >> >> >> >> Just as a hint: for our own, XQuery-based web applications, we have >> >> completely switched over to RESTXQ [2, 3]. >> > >> > >> > I think this is the route I'm going to follow, too. My requirements for >> > the >> > middle layer are rather moderate and can as well be fulfilled by some >> > code >> > that I write in Java instead. >> > >> > I basically wasted my weekend on coding up the new client, but it sure >> > was >> > fun. :) >> > >> > Cheers, >> > Hans > >
FA
Francis Avilain reply to Christian Grün, 25 Feb 2013, 23:4026 Feb 2013 15:17 #
Thanks Christian! What do you think is the best way for a driver to detect whether this feature is available?
Quoted text · Christian Grün · 45 lines
> Hi Hans, hi Francis, > > I decided to refactor our client query api a little: Variables and the > context item can now be rebound, and a query can be run multiple > times. Please note that the semantics of close() is the same as > before: whenever a query is closed, it will completely be unregistered > and is not available for new executions. > > Feedback is welcome, > Christian > ___________________________ > > On Mon, Feb 25, 2013 at 7:59 PM, Hans Hübner <hans.huebner at gmail.com> wrote: >> Hi Christian, >> >> >> On Mon, Feb 25, 2013 at 7:32 PM, Christian Grün <christian.gruen at gmail.com> >> wrote: >>> >>>> https://github.com/hanshuebner/simple-basex >>> >>> thanks for the link; do you want us to add it to our Clients page [1]? >> >> >> I would not mind - The API is different from what the standard BaseX has, >> but I think it is rather easy to use. I may not use it much myself, >> though... >> >>> >>>> But then, >>>> maybe it would be even better to switch to the ReST interface instead. >>> >>> Just as a hint: for our own, XQuery-based web applications, we have >>> completely switched over to RESTXQ [2, 3]. >> >> >> I think this is the route I'm going to follow, too. My requirements for the >> middle layer are rather moderate and can as well be fulfilled by some code >> that I write in Java instead. >> >> I basically wasted my weekend on coding up the new client, but it sure was >> fun. :) >> >> Cheers, >> Hans
-- Francis Avila Senior Developer Dancing Mammoth, Inc. (Formerly PJ Doland Web Design, Inc.) P: 703.621.0990 E: favila at dancingmammoth.com http://dancingmammoth.com
CG
Christian Grün26 Feb 2013 19:07 #
Hi Francis, there’s no official way to check the availability of the feature, so I would suggest to update everything to the latest version. However, all my changes are backward-compatibe, so you shouldn’t encounter any surprises when you don’t use repeated bindings and query executions.
Quoted text · Francis Avila · 61 lines
On Tue, Feb 26, 2013 at 2:17 PM, Francis Avila <favila at dancingmammoth.com> wrote: > Thanks Christian! > > What do you think is the best way for a driver to detect whether this feature is available? > >> Hi Hans, hi Francis, >> >> I decided to refactor our client query api a little: Variables and the >> context item can now be rebound, and a query can be run multiple >> times. Please note that the semantics of close() is the same as >> before: whenever a query is closed, it will completely be unregistered >> and is not available for new executions. >> >> Feedback is welcome, >> Christian >> ___________________________ >> >> On Mon, Feb 25, 2013 at 7:59 PM, Hans Hübner <hans.huebner at gmail.com> wrote: >>> Hi Christian, >>> >>> >>> On Mon, Feb 25, 2013 at 7:32 PM, Christian Grün <christian.gruen at gmail.com> >>> wrote: >>>> >>>>> https://github.com/hanshuebner/simple-basex >>>> >>>> thanks for the link; do you want us to add it to our Clients page [1]? >>> >>> >>> I would not mind - The API is different from what the standard BaseX has, >>> but I think it is rather easy to use. I may not use it much myself, >>> though... >>> >>>> >>>>> But then, >>>>> maybe it would be even better to switch to the ReST interface instead. >>>> >>>> Just as a hint: for our own, XQuery-based web applications, we have >>>> completely switched over to RESTXQ [2, 3]. >>> >>> >>> I think this is the route I'm going to follow, too. My requirements for the >>> middle layer are rather moderate and can as well be fulfilled by some code >>> that I write in Java instead. >>> >>> I basically wasted my weekend on coding up the new client, but it sure was >>> fun. :) >>> >>> Cheers, >>> Hans > > -- > Francis Avila > Senior Developer > Dancing Mammoth, Inc. > (Formerly PJ Doland Web Design, Inc.) > P: 703.621.0990 > E: favila at dancingmammoth.com > http://dancingmammoth.com >

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