On 26 April 2017 at 15:28, Tom Lane <t...@sss.pgh.pa.us> wrote: > Nikhil Sontakke <nikh...@2ndquadrant.com> writes: >> A SELECT query on the newly promoted master on any of the tables involved >> in the 2PC hangs. The hang is due to a loop in >> SubTransGetTopmostTransaction(). Due to incorrect linkages, we get a >> circular reference in parentxid <-> subxid inducing the infinite loop. > > I'm inclined to propose that > > (1) SubTransSetParent should contain an assert that > Assert(TransactionIdFollows(xid, parent)); > There is a similar assertion near one of the call sites, but that's > obviously too far away from the action. > > (2) SubTransGetTopmostTransaction ought to contain an actual runtime > test and ereport (not just Assert) that the parent XID it got from > pg_subtrans precedes the child XID that was looked up. This would > protect us against similar infinite loops in the future. Even without > bugs, such a loop could arise due to corrupted data.
Pretty much what I was thinking. I've added code following Michael and Tom's comments to the previous patch. New patch attached. Passes with and without Nikhil's new test. I plan to apply both patches tomorrow morning my time to give time for further comments. -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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