A hybrid scan approach combined with this idea would fit nicely - provide results for tids that are directly visible and set a bit in a bitmap for those that need recheck and extend recheck to take a bitmap (wait - it already does :-)
- Luke Msg is shrt cuz m on ma treo -----Original Message----- From: Gregory Stark [mailto:[EMAIL PROTECTED] Sent: Wednesday, August 15, 2007 02:58 PM Eastern Standard Time To: Bruce Momjian Cc: PostgreSQL-development Subject: Re: [HACKERS] Another idea for index-only scans "Bruce Momjian" <[EMAIL PROTECTED]> writes: > I have added another idea for index-only scans to the TODO list: > >> A third idea would be for a heap scan to check if all rows are visible >> and if so set a per-table flag which can be checked by index scans. >> Any change to the table would have to clear the flag. To detect >> changes during the heap scan a counter could be set at the start and >> checked at the end --- if it is the same, the table has not been >> modified --- any table change would increment the counter. I think I would prefer to address this in the same infrastructure as the dead-space-map. That way you're not dependent on having no updates happening on the table at all. Any tuples on pages which contain no in-doubt tuples could have their visibility check skipped but when you come across a tuple on a page which has been modified since the last vacuum then you have to check the visibility. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com ---------------------------(end of broadcast)--------------------------- TIP 4: Have you searched our list archives? http://archives.postgresql.org
