On May 21, 2010, at 4:20 , Florian Pflug wrote: > On May 19, 2010, at 2:15 , Florian Pflug wrote: >> On May 17, 2010, at 3:30 , Robert Haas wrote: >>> On Sun, May 16, 2010 at 9:07 PM, Florian Pflug <f...@phlo.org> wrote: >>>> On May 14, 2010, at 22:54 , Robert Haas wrote: >>>>> On Thu, May 13, 2010 at 5:39 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: >>>>>> Florian Pflug <f...@phlo.org> writes: >>>>>>> All in all, I believe that SHARE and UPDATE row-level locks should be >>>>>>> changed to cause concurrent UPDATEs to fail with a serialization >>>>>>> error. >>>>>> >>>>>> I don't see an argument for doing that for FOR SHARE locks, and it >>>>>> already happens for FOR UPDATE (at least if the row actually gets >>>>>> updated). AFAICS this proposal mainly breaks things, in pursuit of >>>>>> an unnecessary and probably-impossible-anyway goal of making FK locking >>>>>> work with only user-level snapshots. >>>>> >>>>> After giving this considerable thought and testing the behavior at >>>>> some length, I think the OP has it right. One thing I sometimes need >>>>> to do is denormalize a copy of a field, e.g. >>>>> >>>>> <snipped example> >>>> >>>> I've whipped up a quick and still rather dirty patch that implements the >>>> behavior I proposed, at least for the case of conflicts between FOR UPDATE >>>> locks and updates. With the patch, any attempt to UPDATE or FOR UPDATE >>>> lock a row that has concurrently been FOR UPDATE locked will cause a >>>> serialization error. (The same for an actually updated row of course, but >>>> that happened before too). >>>> >>>> While this part of the patch was fairly straight forward, make FOR SHARE >>>> conflict too seems to be much harder. The assumption that a lock becomes >>>> irrelevant after the transaction(s) that held it completely is built >>>> deeply into the multi xact machinery that powers SHARE locks. That >>>> machinery therefore assumes that once all members of a multi xact have >>>> completed the multi xact is dead also. But my proposal depends on a >>>> SERIALIZABLE transaction being able to find if any of the lockers of a row >>>> are invisible under it's snapshot - for which it'd need any multi xact >>>> containing invisible xids to outlive its snapshot. >>> >>> Thanks for putting this together. I suggest adding it to the open >>> CommitFest - even if we decide to go forward with this, I don't >>> imagine anyone is going to be excited about changing it during beta. >>> >>> https://commitfest.postgresql.org/action/commitfest_view/open >> >> >> Will do. Thanks for the link. >> >> Here is an updated version that works for SHARE locks too. > > Forgetting to run "make check" before sending a patch is bad, as I just > proved :-( > > For the archives' and the commitfest app's sake, here is a version that > actually passes the regression tests. > > To make up for it, I also did some testing with a custom pgbench script & > schema and proved the effectiveness of this patch. I ran this with "pgbench > -s 10 -j 10 -c 10 -t 1000 -n -f fkbench.pgbench" on both HEAD and HEAD+patch. > The former errors out quickly with "database inconsistent" while the later > completes the pgbench run without errors. > > The patch still needs more work, at least on the comments & documentation > side of things, but I'm going to let this rest now while we're in beta. > > Patch, pgbench script and schema attached.
Great, now my mail client decided to send encode those attachments with MacBinary instead of sending them as plain text :-( Not sure if MUAs other than Mail.app can open those, so I'm resending this. Really sorry for the noise, guys best regards, Florian Pflug
serializable_lock_consistency.patch
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fkbench.init.sql
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fkbench.pgbench
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