[ZODB-Dev] Basic ZODB practices

[Martijn Faassen]

John Belmonte wrote:
> Hector Sanchez SanMartin wrote:
> 
>>    I'm using ZODB and I need to minimise ConflictErrors in my 
>> application so I would like to describe my situation and ask for some 
>> ideas about how could improve it (if possible) in order to minimise 
>> ConflictErrors as I'm sure you have already faced the same problem.

[snip]
> 
> The first course is to avoid sequential ID's completely.  You can use 
> Python's rand library to generate a random ID.  Before inserting an 
> object into your collection, verify that you don't have an ID collision. 
>  Collisions should be extremely rare if you use an ID size such as 64 
> bits.  The BTree will also benefit from having random keys, as this will 
> minimize write conflicts caused by shuffled buckets.

Just out of curiosity:

You'd think random ids could be *bad* for read performance though. If 
there is some sequentiality in the data you're putting in a BTree, and 
you're reading this data in its 'native' sequencing, with random ids 
you'd be waking up a lot of buckets, which hurts read performance. 
Better just wake up a single bucket with the sequential data in there, 
and then read the values. What're people's thoughts on this?

Perhaps related, I recall Tim Peters (I think, might've been someone 
else) once (long ago..) saying random ids don't really help, though I 
forget the exact context. Perhaps Tim remembers and can jump in, but I 
may remember this completely wrong anyway. :)

Regards,

Martijn