Re: BUG #17255: Server crashes in index_delete_sort_cmp() due to race condition with vacuum

Hi,

On 2021-11-13 16:06:40 +0100, Dmitry Dolgov wrote:
> I've got curious if modifying the Alexander's test case could reveal
> something interesting, and sprinkled it with savepoints and rollbacks.
> Almost immediately a new problem has manifested itself, although the
> crash has nothing to do with the disconnected tuples as far as I can
> tell -- still probably worth mentioning. In this case vacuum invoked
> lazy_scan_prune, and during the first scan one of the chains had a
> HEAPTUPLE_DEAD at the third position. The processing flow fell through
> to heap_prune_record_prunable and crashed on an assert with an
> InvalidTransactionId:
> 
>     #3  0x000055a2b260d1f9 in heap_prune_record_prunable (prstate=0x7ffd0c0ecdf0, xid=0) at pruneheap.c:872
>     #4  0x000055a2b260ca72 in heap_prune_chain (buffer=2117, rootoffnum=150, prstate=0x7ffd0c0ecdf0) at
pruneheap.c:695
>     #5  0x000055a2b260bcd6 in heap_page_prune (relation=0x7fb98e217e20, buffer=2117, vistest=0x55a2b31d2d60
<GlobalVisCatalogRels>,old_snap_xmin=0, old_snap_ts=0, report_stats=false, off_loc=0x55a2b3e6a0cc) at pruneheap.c:288
 
>     #6  0x000055a2b261309c in lazy_scan_prune (vacrel=0x55a2b3e6a060, buf=2117, blkno=192, page=0x7fb97856bf80 "",
vistest=0x55a2b31d2d60<GlobalVisCatalogRels>, prunestate=0x7ffd0c0ee9d0) at vacuumlazy.c:1739
 
> 
> Applying heap_prune_record_prunable only if TransactionIdIsNormal seems
> to help. The original implementation didn't reach
> heap_prune_record_prunable either and also doesn't crash.

Does your modified test still find problems with 0001 & 0002 from
https://postgr.es/m/20211211045710.ljtuu4gfloh754rs%40alap3.anarazel.de
applied?

Greetings,

Andres Freund