On Wed, Nov 4, 2020 at 2:18 PM Amit Kapila <amit.kapil...@gmail.com> wrote: > > Or you might want to consider moving the check related to > IsModifySupportedInParallelMode() inside > PrepareParallelModeForModify(). That way the code might look a bit > cleaner. >
Posting an updated Parallel SELECT for "INSERT INTO ... SELECT ..." patch which addresses previously-identified issues and suggestions, and adds some tests and doc updates. I won't post an updated Parallel INSERT patch just yet (which just builds on the 1st patch), because there's at least a couple of issues in this 1st patch which need to be discussed first. Firstly, in order to perform parallel-safety checks in the case of partitions, the patch currently recursively locks/unlocks (AccessShareLock) each partition during such checks (as each partition may itself be a partitioned table). Is there a better way of performing the parallel-safety checks and reducing the locking requirements? Secondly, I found that when running "make check-world", the "partition-concurrent-attach" test fails, because it is expecting a partition constraint to be violated on insert, while an "alter table attach partition ..." is concurrently being executed in another transaction. Because of the partition locking done by the patch's parallel-safety checking code, the insert blocks on the exclusive lock held by the "alter table" in the other transaction until the transaction ends, so the insert ends up successfully completing (and thus fails the test) when the other transaction ends. To overcome this test failure, the patch code was updated to instead perform a conditional lock on the partition, and on failure (i.e. because of an exclusive lock held somewhere else), just assume it's parallel-unsafe because the parallel-safety can't be determined without blocking on the lock. This is not ideal, but I'm not sure of what other approach could be used and I am somewhat reluctant to change that test. If anybody is familiar with the "partition-concurrent-attach" test, any ideas or insights would be appreciated. Regards, Greg Nancarrow Fujitsu Australia
v7-0001-Enable-parallel-SELECT-for-INSERT-INTO-.-SELECT.patch
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v7-0002-Parallel-SELECT-for-INSERT-INTO-.-SELECT-tests-and-doc.patch
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