[pybsddb] Where is the bug tracker? Multi-threaded len() bug

[Jesus Cea]

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On 12/26/2008 06:47 PM, Yong Li wrote:
> Create a dir named "db" in current dir.
> 
> run writer.py
> run reader.py
> you will see that the length displayed by reader.py does not change,
> even as writer is writing to the db.
> Happy holidays and happy bug hunting :)

A year old report, finally analyzed and solved.

Checking the size of a database is potentially slow because it can
require reading the complete file, to know how many items are there. So,
pybsddb was keeping a cached version in RAM, and invalidate that version
when the database is modified.

The problem with this approach is when you have several processes
working on the same database, like your example, since one process
doesn't know the other process has done changes and so it keeps the
cached value as "current".

I have dropped all this code. Now, when you ask for the number of items
in a database, the database is scanned, as it should. This will be
SLOW!. If you need a "len" report accurate and fast, the application
must keep the counter manually in a database register.

This change will be available in pybsddb 4.8.3, to be released
inminently (days).

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