Re: [HACKERS] GSoC on WAL-logging hash indexes

On Wed, Apr 30, 2014 at 5:55 AM, ktm@rice.edu <ktm@rice.edu> wrote:
> I do not think that CPU costs matter as much as the O(1) probe to
> get a result value specifically for very large indexes/tables where
> even caching the upper levels of a B-tree index would kill your
> working set in memory. I know, I know, everyone has so much memory
> and can just buy more... but this does matter.

Have you actually investigated how little memory it takes to store the
inner pages? It's typically less than 1% of the entire index. AFAIK,
hash indexes are not used much in any other system. I think MySQL has
them, and SQL Server 2014 has special in-memory hash table indexes for
in memory tables, but that's all I can find on Google.


--
Peter Geoghegan