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 <[email protected]>
