Thread: pgsql: SSI has a race condition, where the order of commit sequence num
pgsql: SSI has a race condition, where the order of commit sequence num
From
Heikki Linnakangas
Date:
SSI has a race condition, where the order of commit sequence numbers of transactions might not match the order the work done in those transactions become visible to others. The logic in SSI, however, assumed that it does. Fix that by having two sequence numbers for each serializable transaction, one taken before a transaction becomes visible to others, and one after it. This is easier than trying to make the the transition totally atomic, which would require holding ProcArrayLock and SerializableXactHashLock at the same time. By using prepareSeqNo instead of commitSeqNo in a few places where commit sequence numbers are compared, we can make those comparisons err on the safe side when we don't know for sure which committed first. Per analysis by Kevin Grittner and Dan Ports, but this approach to fix it is different from the original patch. Branch ------ master Details ------- http://git.postgresql.org/pg/commitdiff/406d61835b97a801807913e0fc67eadd9c6a3ffa Modified Files -------------- src/backend/storage/lmgr/predicate.c | 29 +++++++++++------------------ src/include/storage/predicate_internals.h | 21 +++++++++++++++++++-- 2 files changed, 30 insertions(+), 20 deletions(-)