Hello David Thank you so much for testing the patch more thoroughly and for sharing your patch. I see that you moved the setting of ParallelBlockTableScanDesc fields from heap_set_tidrange() to be within heap_setscanlimits() so that the missing case of (ItemPointerCompare(&highestItem, &lowestItem) < 0) can be covered. This placement should be fine.
The workers, however, still end up in heap_set_tidrange() during a call to TidRangeNext() via table_rescan_tidrange() at the beginning of the scan as you have described. Each of the worker does attempt to update the tid range to basically the same range to the parallel context shared among the workers in shared memory, which may seem a little racy here. The problem is that the logic in TidRangeNext() is mostly designed as non-parallel mode and that table_rescan_tidrange() is incorrectly called in parallel mode, causing each worker to try to update TID ranges at the same time. The initialization of scan descriptor, rescan and setting TID ranges in fact take place at different places between parallel and non-parallel modes. In non-parallel mode, everything takes place in TidRangeNext() while in parallel mode, they take place in ExecTidRangeScanInitializeDSM() and ExecTidRangeScanReInitializeDSM() and they are called only by the leader. I have updated TidRangeNext() to not do any rescan or set TID limit in parallel mode. I have also updated ExecTidRangeScanInitializeDSM() to set the TID range after initializing parallel scan descriptor, which is shared to the workers via shared memory. Similarly, in ExecTidRangeScanReInitializeDSM(), a new TID range will be set after the re-initialization of parallel scan descriptor during the rescan case. ExecTidRangeScanInitializeWorker() is called by each parallel worker and is also updated such that it will not set the TID limits again. Since ExecTidRangeScanInitializeDSM() and ExecTidRangeScanReInitializeDSM() are only called by the leader process, there will not be any concurrent call to heap_setscanlimits(), so no locking is needed there. On top of the 2 patches you shared, I have attached the third patch with the changes I describe above, so it is easy to spot the new diffs. Thank you once again for your review! Cary
v9-0002-fixup-v7-parallel-TID-range-scan-patch.patch
Description: Binary data
v9-0003-fix-the-incorrect-call-to-scan_set_tidrange.patch
Description: Binary data
v9-0001-v7-parallel-TID-range-scan-patch.patch
Description: Binary data
