Dave Page wrote:
> REINDEX is similar to a drop and recreate of the index in that the index
> contents are rebuilt from scratch. However, the locking considerations
> are rather different. REINDEX locks out writes but not reads of the
> index's parent table. It also takes an exclusive lock on the specific
> index being processed, which will block reads that attempt to use that
> index. In contrast, DROP INDEX momentarily takes exclusive lock on the
> parent table, blocking both writes and reads. The subsequent CREATE
> INDEX locks out writes but not reads; since the index is not there, no
> read will attempt to use it, meaning that there will be no blocking but
> reads may be forced into expensive sequential scans. Another important
> point is that the drop/create approach invalidates any cached query
> plans that use the index, while REINDEX does not.
So the advantage is that drop+create will allow all reads to run
concurrently, though they might have to use sequential scans. Hmm, I
wonder if a CREATE+DROP+rename would be even better. Could use
CONCURRENT-mode in the create as well to allow concurrent writes...
I know I know, no new features at this point :).
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com