Thanks
Tim Peters wrote:
[DJL]
I have a project that i want to export to nokia 770 that use zodb
is there any recommendation to minimize the memory usage of zodb package
Don't store any objects in the database, and don't open any storages or
connections ;-)
Of course those are silly extremes, but they do point to things you have
some control over:
- When a FileStorage is opened, it builds in-memory data structures
to help speed the process of loading persistent data. These
consume memory proportional to the number of unique objects in
the database (e.g., there's an in-memory map from an object's id
(oid) to file offset for the most recent revision of that object).
The more unique objects you create, the more memory this requires.
- Each Connection you open maintains an in-memory cache, mapping
an object id to that object. This can consume an arbitrarily
large amount of RAM: there's no limit on how large an object
may get, so even a 1-object cache could (in theory) consume all
the RAM you have. The fewer connections you have open simultaneously,
the fewer such caches are created. You can limit the size of
the cache via DB's cache_size parameter. This gives a target
number of objects. There is no way to limit cache size by byte
count, and the target number of objects is a soft limit: _during_
a transaction, the cache will hold as many objects as are referenced.
Between transactions, a cache "garbage collection" pass runs
to throw away the least recently referenced excess over cache_size
objects.
So relatively small transactions with relatively small objects
should help.
- Relatedly, use scalable data structures: when possible, use one
of the BTree-based containers instead of a persistent list or dict.
"A BTree" is actually a graph of persistent objects under the covers,
and is specifically designed to consume memory roughly proportional
to the number of containees a transaction _accesses_ (rather than
the-- potentially much larger --total number of containees).
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