[Xapian-discuss] "dangerous" patch

Olly Betts olly at survex.com
Thu Jul 1 19:37:42 BST 2004

On Wed, Jun 30, 2004 at 10:44:07PM +0100, Olly Betts wrote:
> Attached is a patch which turns off the B-tree versioning mechanism
> during update.  You'll lose atomic updates, so if the indexer or machine
> crashes, you've probably got a useless database.  But it reduces the
> number of blocks written which can speed up updating quite a bit if
> it is I/O bound - it's good for reindexing from scratch, for example.
> Here's a couple of graphs showing performance on a fairly low spec
> machine.  The first is without, the second with.  X axis is database
> size, Y axis is documents added per second:
> http://www.survex.com/~olly/dangerous.png
> These graphs don't show off the gain especially well, but they're what
> I have to hand.  Notice how the second graph only drops away from 20
> docs/sec at around 800,000 documents while the first drops below at
> around 350,000.

I realised just overlaying the two graphs would make the difference more
obvious - a couple of minutes with the gimp gives this:


Green is standard, red is "dangerous".


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