On Thu, Jul 30, 2020 at 4:18 PM Mark Dilger <mark.dil...@enterprisedb.com> wrote: > > Maybe I'm just being dense here -- exactly what problem are you worried > > about? > > Per tuple, tuple_is_visible() potentially checks whether the xmin or xmax > committed via TransactionIdDidCommit. I am worried about concurrent > truncation of clog entries causing I/O errors on SLRU lookup when performing > that check. The three strategies I had for dealing with that were taking the > XactTruncationLock (formerly known as CLogTruncationLock, for those reading > this thread from the beginning), locking out vacuum, and the idea upthread > from Andres about setting PROC_IN_VACUUM and such. Maybe I'm being dense and > don't need to worry about this. But I haven't convinced myself of that, yet.
I don't get it. If you've already checked that the XIDs are >= relfrozenxid and <= ReadNewFullTransactionId(), then this shouldn't be a problem. It could be, if CLOG is hosed, which is possible, because if the table is corrupted, why shouldn't CLOG also be corrupted? But I'm not sure that's what your concern is here. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
