From: | Bruce Momjian <bruce(at)momjian(dot)us> |
---|---|
To: | Wei Shan <weishan(dot)ang(at)gmail(dot)com> |
Cc: | Sameer Kumar <sameer(dot)kumar(at)ashnik(dot)com>, pgsql-novice(at)postgresql(dot)org |
Subject: | Re: Why is Hash index not transaction safe. |
Date: | 2015-05-09 23:17:10 |
Message-ID: | 20150509231710.GA30713@momjian.us |
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Lists: | pgsql-novice |
On Wed, May 6, 2015 at 02:02:23PM +0800, Wei Shan wrote:
> Hi Sameer,
>
> Nice to see you around!
>
> The developer wanted to use HASH indexes as the query hitting some columns are
> only using equality comparison (=). They said that HASH has a speed of O(1)
> whereas B-Tree has a speed of logarithm. I believe it's true if you look
> fundamentally at hashtable and B-Tree algorithm.
>
> However, I did my research and found that HASH index has minimal perfomance
> improvement over B-Tree in equality comparison.
>
> Thus, we dropped the idea already :)
Yes, we have heard this many times, and PG 9.5 will issue a warning if
you create a hash index:
WARNING: hash indexes are not WAL-logged and their use is discouraged
--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ Everyone has their own god. +
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