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Re: svn commit: r986865 - /subversion/trunk/notes/wc-ng/node-data

From: Philip Martin <philip.martin_at_wandisco.com>
Date: Thu, 19 Aug 2010 16:56:00 +0100

"Bert Huijben" <bert_at_vmoo.com> writes:

> How would this handle deleted nodes in one layer (then some overlays) and
> then calling _read_children(). I think that would become a union/select over
> multiple layers? We already had some performance issues there in the past
> and I hope this only makes this query easier. (SELECT DISTINCT name where
> parent_relpath=? or something)
>
> Before this new idea I expected that we didn't have to query the NODE_DATA
> if you were just querying _read_info() for kind and status. So for those two
> most common fields I didn't expect any slowdown over the current model.
> With moving everything in one table we will need the sqlite index for
> optimization in a few more cases to keep the same speed. (I think SQLite can
> handle this for us as one of the nice features of using a real database, but
> nevertheless, I think we should try to verify this before moving everything
> into one table)

I'm not an SQL expert, much less an SQLite expert, however BASE_NODE
is still available by adding op_depth=0 to the query. WORKING_NODE is
a bit more complicated as one needs to get the biggest op_depth>0, so
select op_depth>0, order by op_depth and limit to 1. Obviously we
will have to include op_depth in the SQLite index.

In cases such as _read_info where both BASE_NODE and WORKING_NODE are
required we can ask for the biggest op_depth first and if this turns
out to be zero then we find out that there is no WORKING_NODE and get
the BASE_NODE with one query. For unmodified nodes this might be
faster than separate BASE/WORKING.

I'm not sure how _read_children would be affected. SELECT DISTINCT
probably allows us to count them, but I don't know how to construct
the query to return the greatest op_depth for each name.

-- 
Philip
Received on 2010-08-19 17:56:59 CEST

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