Unless there is a sense that this is a bad idea I will submit a doc patch. On Mon, Feb 15, 2016 at 8:22 PM, Chris Travers <chris.trav...@gmail.com> wrote:
> Hi; > > Today I ran into a question from a client as to why an index was not > used. The index had been freshly created and was on a relatively small > table (16k live rows, but 300k dead tuples). The resulting sequential scan > was taking half a second. > > I found that even when setting enable_seqscan to off it was still refusing > to use the index. After reading carefully through the index documentation > yet again, it was not clear why it was not used. > > After much research I came across an email by Tom Lane about how the HOT > enhancements in 8.3 meant that indexes might not be usable until after the > longest running transaction committed. This turned out to be the culpret > (we had a transaction that took about 15 hours to complete and when it > committed the index was used). > > It might help if there is a note that indexes in some cases cannot be used > until the min xid advances to the point where the index was created. > > -- > Best Wishes, > Chris Travers > > Efficito: Hosted Accounting and ERP. Robust and Flexible. No vendor > lock-in. > http://www.efficito.com/learn_more > -- Best Wishes, Chris Travers Efficito: Hosted Accounting and ERP. Robust and Flexible. No vendor lock-in. http://www.efficito.com/learn_more
