[Xapian-discuss] Long query times

[Olly Betts]

On Thu, Sep 29, 2005 at 11:00:21AM -0400, tech at dbx.co.uk wrote:
> annoyingly it doesn't seem to be down to the complexity of the query -more
> to the frequency of term, a few stats :
>  a query for the single term sales takes 25-20s wheras  account
> manager,sales,telecoms takes 1s

A more complex query can often be faster as the matcher is more likely
to be able to terminate early.  A single term query sorted by relevance
will have to process the whole posting list for that term.

The other effect to beware of is that a search from cold can be much
slower.  Once a few queries have been run, you'll have cached a
significant number of the "branch" Btree blocks and searches become a
lot faster.

The new Flint backend should fit noticably more branches into a branch
block which should reduce this effect (as well as making things generally
smaller and faster).

> I'm trying the compaction today -using quartzcompact. Is it the case that I
> can update an index once compacted if I use the -n flag?

You can update any compacted index, but if you do plan to update I'd
avoid the "fuller" compaction option (it typically doesn't save much
extra space anyway).  Updating a database with either full compaction
and non-full compaction should be fine.

Cheers,
    Olly