Re: [Tracker] Parser stack overflow

[Jürg Billeter <j bitron ch>]

On Thu, 2009-12-24 at 22:06 +0200, Debarshi Ray wrote:
> Somewhere in my program I have a query like this:
>
>     return Glib::ustring::compose(
>         "SELECT ?camera ?exposure ?fn ?focal ?iso ?metering ?white"
>               "WHERE {"
>         "  ?photo nie:isStoredAs '%1' ."
>         "  OPTIONAL { ?photo nmm:camera ?camera . }"
>         "  OPTIONAL { ?photo nmm:exposureTime ?exposure . }"
>         "  OPTIONAL { ?photo nmm:fnumber ?fn . }"
>         "  OPTIONAL { ?photo nmm:focalLength ?focal . }"
>         "  OPTIONAL { ?photo nmm:isoSpeed ?iso . }"
>         "  OPTIONAL { ?photo nmm:meteringMode ?metering . }"
>         "  OPTIONAL { ?photo nmm:whiteBalance ?white . }"
>         "}",
>         uri_);
>
> This causing "parser stack overflow" to be reported in
> ~/.local/share/tracker/tracker-store.log:
>
> [...]
> t13_g."photo_u" = t14_g."photo_u"))': parser stack overflow
>
> It is the last OPTIONAL clause that is causing the problem.

This is a SQLite limitation, which can be avoided by increasing
YYSTACKDEPTH when compiling SQLite. However, the better solution is to
slightly modify the SPARQL query to reduce the complexity of the
generated SQL query. If you add `?photo a nmm:Photo .` right after
`WHERE {`, you shouldn't have any issues with parser stack overflows
anymore.

JÃrg