Re: [HACKERS] HOT updates REDIRECT line pointers

2012-04-09 Thread Bruce Momjian
On Wed, Mar 21, 2012 at 09:28:22PM -0400, Robert Haas wrote: On Wed, Mar 21, 2012 at 9:22 PM, Tom Lane t...@sss.pgh.pa.us wrote: It strikes me that it likely wouldn't be any worse than, oh, say, flipping the default value of standard_conforming_strings, Really?  It's taking away

Re: [HACKERS] HOT updates REDIRECT line pointers

2012-03-22 Thread Simon Riggs
On Thu, Mar 22, 2012 at 1:28 AM, Robert Haas robertmh...@gmail.com wrote: On Wed, Mar 21, 2012 at 9:22 PM, Tom Lane t...@sss.pgh.pa.us wrote: It strikes me that it likely wouldn't be any worse than, oh, say, flipping the default value of standard_conforming_strings, Really?  It's taking away

Re: [HACKERS] HOT updates REDIRECT line pointers

2012-03-22 Thread Merlin Moncure
On Wed, Mar 21, 2012 at 8:28 PM, Robert Haas robertmh...@gmail.com wrote: On Wed, Mar 21, 2012 at 9:22 PM, Tom Lane t...@sss.pgh.pa.us wrote: It strikes me that it likely wouldn't be any worse than, oh, say, flipping the default value of standard_conforming_strings, Really?  It's taking away

Re: [HACKERS] HOT updates REDIRECT line pointers

2012-03-22 Thread Robert Haas
On Thu, Mar 22, 2012 at 9:31 AM, Simon Riggs si...@2ndquadrant.com wrote: Surely it just stops you using that idea 100% of the time. I don't see why you can't have this co-exist with the current mechanism. So it doesn't kill it for the common case. I guess you could use it if you knew that

Re: [HACKERS] HOT updates REDIRECT line pointers

2012-03-22 Thread Pavan Deolasee
On Thu, Mar 22, 2012 at 6:58 AM, Robert Haas robertmh...@gmail.com wrote: On Wed, Mar 21, 2012 at 9:22 PM, Tom Lane t...@sss.pgh.pa.us wrote: It strikes me that it likely wouldn't be any worse than, oh, say, flipping the default value of standard_conforming_strings, Really? It's

[HACKERS] HOT updates REDIRECT line pointers

2012-03-21 Thread Robert Haas
When the root tuple of a HOT chain is dead, but there's still at least one non-dead member of the chain, we end up with a REDIRECT line pointer, which points to a USED line pointer, which in turn points to a live tuple. This means we're using 2 line pointers for only 1 line tuple. Since line

Re: [HACKERS] HOT updates REDIRECT line pointers

2012-03-21 Thread Tom Lane
Robert Haas robertmh...@gmail.com writes: Specifically, I'm wondering if we couldn't get away with rearranging things so that the root line pointer (which has index entries) points to the actual tuple, and the other line pointer (which can't have any index entries) gets marked UNUSED. This

Re: [HACKERS] HOT updates REDIRECT line pointers

2012-03-21 Thread Tom Lane
I wrote: Robert Haas robertmh...@gmail.com writes: Specifically, I'm wondering if we couldn't get away with rearranging things so that the root line pointer (which has index entries) points to the actual tuple, and the other line pointer (which can't have any index entries) gets marked

Re: [HACKERS] HOT updates REDIRECT line pointers

2012-03-21 Thread Robert Haas
On Wed, Mar 21, 2012 at 8:13 PM, Tom Lane t...@sss.pgh.pa.us wrote: I wrote: Robert Haas robertmh...@gmail.com writes: Specifically, I'm wondering if we couldn't get away with rearranging things so that the root line pointer (which has index entries) points to the actual tuple, and the other

Re: [HACKERS] HOT updates REDIRECT line pointers

2012-03-21 Thread Tom Lane
Robert Haas robertmh...@gmail.com writes: On Wed, Mar 21, 2012 at 8:13 PM, Tom Lane t...@sss.pgh.pa.us wrote: Another issue, quite independent from race conditions against other observers of the row, is what if the tuple is part of an update chain? You have no way to find the predecessor row

Re: [HACKERS] HOT updates REDIRECT line pointers

2012-03-21 Thread Robert Haas
On Wed, Mar 21, 2012 at 8:44 PM, Tom Lane t...@sss.pgh.pa.us wrote: Oh, right.  So scratch that objection.  The other one is still fatal though ... So, could we just decide that we don't care about preserving that property any more, and document it as an incompatibility in whatever release we

Re: [HACKERS] HOT updates REDIRECT line pointers

2012-03-21 Thread Tom Lane
Robert Haas robertmh...@gmail.com writes: On Wed, Mar 21, 2012 at 8:44 PM, Tom Lane t...@sss.pgh.pa.us wrote: Oh, right. So scratch that objection. The other one is still fatal though ... So, could we just decide that we don't care about preserving that property any more, and document it

Re: [HACKERS] HOT updates REDIRECT line pointers

2012-03-21 Thread Robert Haas
On Wed, Mar 21, 2012 at 9:22 PM, Tom Lane t...@sss.pgh.pa.us wrote: It strikes me that it likely wouldn't be any worse than, oh, say, flipping the default value of standard_conforming_strings, Really?  It's taking away functionality and not supplying any substitute (or at least you did not