Subject: Re: [boost] persistence library proposal (with prototypeimplementation)
From: Ilya Bobir (ilya.bobir_at_[hidden])
Date: 2009-08-10 19:03:32
Stefan Strasser wrote:
> with very poor performance, but that's mostly due to the current storage
> backend, using one file for each object, so you end up with thousands of
> files, a few bytes each.
I think it is OK for a prototype to be slow.
Postgres uses a hierarchy of caches for all the data stored it tables.
And when it does read from the disk it reads a "page" that may contain
data that belongs to another tuples in addition to the data for the
target tuple. Other databases probably do something similar.
The data read from the disk is not transformed unless some logic
requires value of the exact attribute of a tuple. To get an attribute
value you have to ask the cache subsystem for the attribute. During
this call the value may be transformed from the on disk representation
or may be just found in the cache.
I know that writes are also done in pages. But I do not know the exact
What I'm trying to say is that the performance can be considerably
improved without changing the user interface but a fast implementation
will probably require a lot of effort.
Thought unless you track individual fields you will have to load objects
as a whole. And you will probably have to write your own
serialization layer as the boost::serialization library will not allow
you to do this kind of optimizations.
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