Re: index-only scans vs. Hot Standby, round two
| От | Simon Riggs |
|---|---|
| Тема | Re: index-only scans vs. Hot Standby, round two |
| Дата | |
| Msg-id | CA+U5nMLY0nz-Y=+cyv9BAqYvWm+S9=zWXms9HAMfCBGgP7uNFA@mail.gmail.com обсуждение исходный текст |
| Ответ на | index-only scans vs. Hot Standby, round two (Robert Haas <robertmhaas@gmail.com>) |
| Список | pgsql-hackers |
On Fri, Apr 13, 2012 at 5:33 PM, Robert Haas <robertmhaas@gmail.com> wrote: > Currently, we have a problem with index-only scans in Hot Standby > mode: the xmin horizon on the standby might lag the master, and thus > an index-only scan might mistakenly conclude that no heap fetch is > needed when in fact it is. I suggested that we handle this by > suppressing generation of index-only scan plans in Hot Standby mode, > but Simon, Noah, and Dimitri were arguing that we should instead do > the following, which is now on the open items list: > > * Make XLOG_HEAP2_VISIBLE records generate recovery snapshot conflicts > so that IndexOnlyScans work on Hot Standby ... <snip> very long email </snip> Luckily its much simpler than all of that suggests. It'll take a few hours for me to write a short reply but its Sunday today, so that will happen later. -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
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