Roché Compaan wrote at 2008-8-23 19:31 +0200:
>On Sat, 2008-08-23 at 14:09 +0200, Dieter Maurer wrote:
>> Roché Compaan wrote at 2008-8-22 14:49 +0200:
>> >I've been doing some benchmarks on Plone and got some surprising stats
>> >on the pickle size of btrees and their buckets that are persisted with
>> >each transaction. Surprising in the sense that they are very big in
>> >relation to the actual data indexed. I would appreciate it if somebody
>> >can help me understand what is going on, or just take a look to see if
>> >the sizes look normal.
>> >
>> >In the benchmark I add and index 10000 ATDocuments. I commit after each
>> >document to simulate a transaction per request environment. Each
>> >document has a 100 byte long description and 100 bytes in it's body. The
>> >total transaction size however is 40K in the beginning. The transaction
>> >sizes grow linearly to about 350K when reaching 10000 documents.
>> The "Bucket" nodes store usually between 22 ("OOBucket") and 90 ("IIBucket")
>> objects in a single bucket.
>> With any change, the transaction will contain unmodified data
>> for several dozens other objects.
>Are you saying *all* 22 OOBuckets and 90 IIBuckets will be persisted
>again whether they are modified or not?

I did not speak of "22 OOBuckets" but of typically 22 entries in an
"OOBucket" (similarly for "IIBucket").

And indeed, when a single entry in an "OOBucket" is changed, then all
entries are rewritten even if the other entries did not change.

That is because the ZODB load/store granularity is the persistent object
(without persistent subobjects). An "OOBucket" is a persistent object --
it is loaded/stored always as a whole (all entries together).

For more information about ZODB, see the ZODB Wiki:

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