10 Commits (31e8ab4dd98dbe702df8b2029cf6e2424b12850e)

Author	SHA1	Message	Date
Heikki Linnakangas	cb94db91b2	pgindent run of recent SSI changes. Also, remove an unnecessary #include. ... Kevin Grittner	15 years ago
Heikki Linnakangas	264a6b127a	The rolled-back flag on serializable xacts was pointless and redundant with ... the marked-for-death flag. It was only set for a fleeting moment while a transaction was being cleaned up at rollback. All the places that checked for the rolled-back flag should also check the marked-for-death flag, as both flags mean that the transaction will roll back. I also renamed the marked-for-death into "doomed", which is a lot shorter name.	15 years ago
Heikki Linnakangas	cb2d158c58	Fix locking while setting flags in MySerializableXact. ... Even if a flag is modified only by the backend owning the transaction, it's not safe to modify it without a lock. Another backend might be setting or clearing a different flag in the flags field concurrently, and that operation might be lost because setting or clearing a bit in a word is not atomic. Make did-write flag a simple backend-private boolean variable, because it was only set or tested in the owning backend (except when committing a prepared transaction, but it's not worthwhile to optimize for the case of a read-only prepared transaction). This also eliminates the need to add locking where that flag is set. Also, set the did-write flag when doing DDL operations like DROP TABLE or TRUNCATE -- that was missed earlier.	15 years ago
Heikki Linnakangas	c79c570bd8	Small comment fixes and enhancements.	15 years ago
Heikki Linnakangas	8f9622bbb3	Make DDL operations play nicely with Serializable Snapshot Isolation. ... Truncating or dropping a table is treated like deletion of all tuples, and check for conflicts accordingly. If a table is clustered or rewritten by ALTER TABLE, all predicate locks on the heap are promoted to relation-level locks, because the tuple or page ids of any existing tuples will change and won't be valid after rewriting the table. Arguably ALTER TABLE should be treated like a mass-UPDATE of every row, but if you e.g change the datatype of a column, you could also argue that it's just a change to the physical layout, not a logical change. Reindexing promotes all locks on the index to relation-level lock on the heap. Kevin Grittner, with a lot of cosmetic changes by me.	15 years ago
Heikki Linnakangas	c8630919e0	SSI comment fixes and enhancements. Notably, document that the conflict-out ... flag actually means that the transaction has a conflict out to a transaction that committed before the flagged transaction. Kevin Grittner	15 years ago
Bruce Momjian	bf50caf105	pgindent run before PG 9.1 beta 1.	15 years ago
Heikki Linnakangas	47ad79122b	Fix bugs in Serializable Snapshot Isolation. ... Change the way UPDATEs are handled. Instead of maintaining a chain of tuple-level locks in shared memory, copy any existing locks on the old tuple to the new tuple at UPDATE. Any existing page-level lock needs to be duplicated too, as a lock on the new tuple. That was neglected previously. Store xmin on tuple-level predicate locks, to distinguish a lock on an old already-recycled tuple from a new tuple at the same physical location. Failure to distinguish them caused loops in the tuple-lock chains, as reported by YAMAMOTO Takashi. Although we don't use the chain representation of UPDATEs anymore, it seems like a good idea to store the xmin to avoid some false positives if no other reason. CheckSingleTargetForConflictsIn now correctly handles the case where a lock that's being held is not reflected in the local lock table. That happens if another backend acquires a lock on our behalf due to an UPDATE or a page split. PredicateLockPageCombine now retains locks for the page that is being removed, rather than removing them. This prevents a potentially dangerous false-positive inconsistency where the local lock table believes that a lock is held, but it is actually not. Dan Ports and Kevin Grittner	15 years ago
Heikki Linnakangas	f9f9d696a9	UINT64_MAX isn't defined on MSVC.	15 years ago
Heikki Linnakangas	dafaa3efb7	Implement genuine serializable isolation level. ... Until now, our Serializable mode has in fact been what's called Snapshot Isolation, which allows some anomalies that could not occur in any serialized ordering of the transactions. This patch fixes that using a method called Serializable Snapshot Isolation, based on research papers by Michael J. Cahill (see README-SSI for full references). In Serializable Snapshot Isolation, transactions run like they do in Snapshot Isolation, but a predicate lock manager observes the reads and writes performed and aborts transactions if it detects that an anomaly might occur. This method produces some false positives, ie. it sometimes aborts transactions even though there is no anomaly. To track reads we implement predicate locking, see storage/lmgr/predicate.c. Whenever a tuple is read, a predicate lock is acquired on the tuple. Shared memory is finite, so when a transaction takes many tuple-level locks on a page, the locks are promoted to a single page-level lock, and further to a single relation level lock if necessary. To lock key values with no matching tuple, a sequential scan always takes a relation-level lock, and an index scan acquires a page-level lock that covers the search key, whether or not there are any matching keys at the moment. A predicate lock doesn't conflict with any regular locks or with another predicate locks in the normal sense. They're only used by the predicate lock manager to detect the danger of anomalies. Only serializable transactions participate in predicate locking, so there should be no extra overhead for for other transactions. Predicate locks can't be released at commit, but must be remembered until all the transactions that overlapped with it have completed. That means that we need to remember an unbounded amount of predicate locks, so we apply a lossy but conservative method of tracking locks for committed transactions. If we run short of shared memory, we overflow to a new "pg_serial" SLRU pool. We don't currently allow Serializable transactions in Hot Standby mode. That would be hard, because even read-only transactions can cause anomalies that wouldn't otherwise occur. Serializable isolation mode now means the new fully serializable level. Repeatable Read gives you the old Snapshot Isolation level that we have always had. Kevin Grittner and Dan Ports, reviewed by Jeff Davis, Heikki Linnakangas and Anssi Kääriäinen	15 years ago