Re: [basex-talk] Optimization of a slow query with `//`

I don't have any TEI documents at hand, but maybe something like:

/tei:TEI/tei:text/tei:body //*[starts-with(@xml:lang, "san")] //(tei:entry | tei:re) [./tei:form/tei:orth = "arci"]

That would select (I believe) all elements with @xml:lang starting with "san" that have as a descendant either a tei:entry or tei:re who's tei:form/tei:orth is "arci".

I guess you could do the other way around as well, to first select everything that has it's tei:orth = "arci", and limit it with you specified language. That might be faster depending if there are more few tei:orth = "arci" elements, than there is elements with their @xml:lang starting with "san".

I hope I don't lie and assume too much here. Kristian K

12.06.2015 11:42, Gioele Barabucci kirjutas:

Hello,

I am working on an application that retrieves its data from a TEI XML file via BaseX. The following query lies at the core of this application but is too slow to be used in production: on a modern PC it requires about 600 ms to run over a 4MB file (1/10 of the complete dataset). Any suggestion on how to improve its performance (without changing the underlying TEI files) would be much appreciated.

Here is the query:

declare namespace tei='http://www.tei-c.org/ns/1.0';

/tei:TEI/tei:text/tei:body//
  *[self::tei:entry or self::tei:re]
  [./tei:form/tei:orth[. = "arci"]
    [ancestor-or-self::*
      [@xml:lang][1]
      [(starts-with(@xml:lang, "san"))]
    ]
  ]

In human terms is should return all the `tei:entry` or `tei:re` that

• have the word "arci" in their `/tei:form/tei:orth` element,
• their nearest `xml:lang` attribute starts with 'san'.

I made some tests and it turned out that the main culprit is the use of `//` in the first line. (_Main_ culprit, not the only one...)

I use the `//` axis because I do not know what is the structure of the underlying TEI file. I expect BaseX to keep track of all the `tei:entry` and `tei:re` elements and their parents, so selecting the correct ones should be quite fast anyway. But the measurements disagree with my assumptions...

What could I do to improve the performance of this query?

Now, some remarks based on some small tests I have done:

1. Removing the

   [ancestor-or-self::*[....]]

predicate slashes the run time in half, but the query is still way too slow.

2. Changing

   ./tei:form/tei:orth[. = "arci"]

to

./tei:form[1]/tei:orth[1][. = "arci"]

makes the query even slower.

3. changing `starts-with(@xml:lang, "san")` to `@xml:lang = 'san-xxx'`

has a negligible effect.

4. Dropping the `[1]` from

   [@xml:lang][1]

makes the whole query twice as fast.

Regards,

-- Gioele Barabucci gioele@svario.it