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

1 files changed, 18 insertions, 0 deletions

diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 7b3787a66ec..b73262d8629 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -795,6 +795,7 @@ LINE
 LOCALLOCK
 LOCALLOCKOWNER
 LOCALLOCKTAG
+LOCALPREDICATELOCK
 LOCK
 LOCKMASK
 LOCKMETHODID
@@ -931,6 +932,7 @@ OffsetNumber
 OffsetVarNodes_context
 Oid
 OidOptions
+OldSerXidControlData
 OldToNewMapping
 OldToNewMappingData
 OldTriggerInfo
@@ -1081,6 +1083,10 @@ PQconninfoOption
 PQnoticeProcessor
 PQnoticeReceiver
 PQprintOpt
+PREDICATELOCK
+PREDICATELOCKTAG
+PREDICATELOCKTARGET
+PREDICATELOCKTARGETTAG
 PROC
 PROCESS_INFORMATION
 PROCLOCK
@@ -1202,6 +1208,9 @@ PreParseColumnRefHook
 PredClass
 PredIterInfo
 PredIterInfoData
+PredXactListData
+PredXactListElementData
+PredicateLockData
 PrepareStmt
 PreparedParamsData
 PreparedStatement
@@ -1268,6 +1277,8 @@ RSA
 RTEKind
 RUHashEntry
 RUHashEntryData
+RWConflictData
+RWConflictPoolHeaderData
 RangeFunction
 RangeQueryClause
 RangeSubselect
@@ -1350,6 +1361,10 @@ RunningTransactionsData
 SC_HANDLE
 SECURITY_ATTRIBUTES
 SEG
+SERIALIZABLEXACT
+SERIALIZABLEXACTTAG
+SERIALIZABLEXID
+SERIALIZABLEXIDTAG
 SERVICE_STATUS
 SERVICE_STATUS_HANDLE
 SERVICE_TABLE_ENTRY
@@ -1595,6 +1610,9 @@ TwoPhaseCallback
 TwoPhaseFileHeader
 TwoPhaseLockRecord
 TwoPhasePgStatRecord
+TwoPhasePredicateLockRecord
+TwoPhasePredicateRecord
+TwoPhasePredicateXactRecord
 TwoPhaseRecordOnDisk
 TwoPhaseRmgrId
 TwoPhaseStateData