Support synchronization of snapshots through an export/import procedure.

A transaction can export a snapshot with pg_export_snapshot(), and then
others can import it with SET TRANSACTION SNAPSHOT.  The data does not
leave the server so there are not security issues.  A snapshot can only
be imported while the exporting transaction is still running, and there
are some other restrictions.

I'm not totally convinced that we've covered all the bases for SSI (true
serializable) mode, but it works fine for lesser isolation modes.

Joachim Wieland, reviewed by Marko Tiikkaja, and rather heavily modified
by Tom Lane

1 files changed, 7 insertions, 1 deletions

diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index a11d4385b7d..71c82437cdf 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -37,10 +37,16 @@ extern void ExpireTreeKnownAssignedTransactionIds(TransactionId xid,
 extern void ExpireAllKnownAssignedTransactionIds(void);
 extern void ExpireOldKnownAssignedTransactionIds(TransactionId xid);
 
-extern RunningTransactions GetRunningTransactionData(void);
+extern int	GetMaxSnapshotXidCount(void);
+extern int	GetMaxSnapshotSubxidCount(void);
 
 extern Snapshot GetSnapshotData(Snapshot snapshot);
 
+extern bool ProcArrayInstallImportedXmin(TransactionId xmin,
+										 TransactionId sourcexid);
+
+extern RunningTransactions GetRunningTransactionData(void);
+
 extern bool TransactionIdIsInProgress(TransactionId xid);
 extern bool TransactionIdIsActive(TransactionId xid);
 extern TransactionId GetOldestXmin(bool allDbs, bool ignoreVacuum);