Hi Bram,
not being much into the issue of creating databases at this scale I'm not sure whether the OOM problems you are facing are related to Basex of JVM actually.
Anyway something rather simple you could try is to behave "in between".
Instead of opening a single session for the create statements alltogether or one session for each and every create, you could split your create statements in chunks of 100/1000 or the like and distribute them over subsequent (or maybe even parallel?) sessions....
I'm not sure whether this is applicable for your use case though.

On 15/10/2016 10:48, Bram Vanroy | KU Leuven wrote:

Hi all

I’ve talked before on how we restructured our data to drastically improve search times on a 500 million token corpus. [1] Now, after some minor improvements, I am trying to import the generated XML files into BaseX. The result would be 100,00s to millions of BaseX databases – as we expect. When doing the import, though, I am running into OOM errors. We put our memory limit on 512MB. The thing is that this seems incredibly odd to me: because we are creating so many different databases, which are all really small as a consequence, I would not expect BaseX to need to store much in memory. After each database is created, the garbage collector can come along and remove everything that was needed for the previously generated database.

A solution, I suppose, would be to close and open the BaseX session on each creation but I’m afraid that (on such a huge scale) the impact on speed would be too large. How it is set up now, in pseudo code:


$session = Session->new(host, port, user, pw);

# @allFiles is at least 100,000 items

For $file (@allFiles) {

    $database_name = $file . “name”;

$session->execute("CREATE DB $database_name file ");





So all databases are created on the same session which I believe causes the issue. But why? What is still required in memory after ->execute(“CLOSE”)? Are the indices for the generated databases stored in memory? *If so, can we force them to write to disk?*

ANY thoughts on this are appreciated. Enlightenment on how what is stored in a Session’s memory is useful as well. Increasing the memory should be a last resort.

Thank you in advance!


[1]: http://www.lrec-conf.org/proceedings/lrec2014/workshops/LREC2014Workshop-CMLC2%20Proceedings-rev2.pdf#page=20

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