Xapian discuss - Feb 2014 - Fwd: inmemory throwing DatabaseModifiedError

Hi,

I have a weird situation with an inmemory database, which appears to be
throwing a DatabaseModifiedError.  I had a look at the Xapian test code and
found a comment that said:

// Inmemory never throws DatabaseModifiedError

But my code (PHP bindings):

$xapian_database = Xapian\Xapian::inmemory_open();
$xapian_database->add_document($xdoc);
$xapian_database->commit();

Is throwing:

DatabaseModifiedError: The revision being read has been discarded - you
should call Xapian::Database::reopen() and retry the operation

On the add_document line.  Here's a backtrace:

#0: writabledatbase_add_document() in
/vendor/ftlabs/xapian-query/src/Xapian/XapianWritableDatabase.php:40
#1: add_document() in /app/classes/XapianDatabases:111
#2: filterQueriesForPost() in
/app/classes/indexingjobs/XapianStreamFinder.php:38

Any idea why this error would be thrown by an inmemory database?  As I
understand it, there should be no reason why this database is subject to
interference outside of the process that creates it.  In practice, these
errors are occurring when we have a large number of inmemory databases
being created and destroyed at the same time, so is there any way they
could be clashing?

Andrew

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On Tue, Feb 11, 2014 at 08:12:25AM +0000, Andrew Betts
wrote:
> I have a weird situation with an inmemory database, which appears to be
> throwing a DatabaseModifiedError.  I had a look at the Xapian test code and
> found a comment that said:
> 
> // Inmemory never throws DatabaseModifiedError
That should be correct.
> But my code (PHP bindings):
> 
> $xapian_database = Xapian\Xapian::inmemory_open();
The PHP bindings aren't currently in a namespace, so it looks like
you're not using the code as we ship it, which makes it harder to say
what might be causing this.
> $xapian_database->add_document($xdoc);
> $xapian_database->commit();
> 
> Is throwing:
> 
> DatabaseModifiedError: The revision being read has been discarded - you
> should call Xapian::Database::reopen() and retry the operation
In the code as shipped, that error message is only in the disk-based
backends (this is for 1.2 branch; trunk is much the same though):

$ git grep 'revision being read'
backends/brass/brass_table.cc:    throw Xapian::DatabaseModifiedError("The
revision being read has been discarded - you should call
Xapian::Database::reopen() and retry the operation");
backends/chert/chert_table.cc:    throw Xapian::DatabaseModifiedError("The
revision being read has been discarded - you should call
Xapian::Database::reopen() and retry the operation");
backends/flint/flint_table.cc:    throw Xapian::DatabaseModifiedError("The
revision being read has been discarded - you should call
Xapian::Database::reopen() and retry the operation");

So I'd guess that $xapian_database isn't actually an inmemory database.
> Any idea why this error would be thrown by an inmemory database?  As I
> understand it, there should be no reason why this database is subject to
> interference outside of the process that creates it.  In practice, these
> errors are occurring when we have a large number of inmemory databases
> being created and destroyed at the same time, so is there any way they
> could be clashing?
They shouldn't be able to clash.

Cheers,
    Olly