Fix snapshot import xmin ProcArrayLock bug. ProcArrayInstallImportedXmin verifies that the source transaction (the transaction whose snapshot we're importing) is still running, and then installs the caller's imported xmin. These steps have to be atomic. But it was just about possible for VACUUM to fail to observe the imported xmin in either the source proc or the importing one. This could result in VACUUM pruning away deleted tuples that were still visible to the imported snapshot.
To fix, take ProcArrayLock in exclusive mode while importing an exported snapshot's xmin within ProcArrayInstallImportedXmin. That guarantees that a concurrent VACUUM's OldestXmin cannot advance past the xmin (one proc or the other always advertises an xmin that holds it back). Author: Chee Wooson <[email protected]> Reviewed-by: Peter Geoghegan <[email protected]> Discussion: https://postgr.es/m/[email protected] Backpatch-through: 14 Branch ------ REL_18_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/3977cde272bc38d33d73bc8c9ff5c1156fb95342 Modified Files -------------- src/backend/storage/ipc/procarray.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
