Efficient transaction-controlled synchronous replication.

If a standby is broadcasting reply messages and we have named
one or more standbys in synchronous_standby_names then allow
users who set synchronous_replication to wait for commit, which
then provides strict data integrity guarantees. Design avoids
sending and receiving transaction state information so minimises
bookkeeping overheads. We synchronize with the highest priority
standby that is connected and ready to synchronize. Other standbys
can be defined to takeover in case of standby failure.

This version has very strict behaviour; more relaxed options
may be added at a later date.

Simon Riggs and Fujii Masao, with reviews by Yeb Havinga, Jaime
Casanova, Heikki Linnakangas and Robert Haas, plus the assistance
of many other design reviewers.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/include/storage/shmem.h b/src/include/storage/shmem.h
index f23740c9e3c..0b7da77ccd8 100644
--- a/src/include/storage/shmem.h
+++ b/src/include/storage/shmem.h
@@ -67,8 +67,11 @@ extern void SHMQueueInit(SHM_QUEUE *queue);
 extern void SHMQueueElemInit(SHM_QUEUE *queue);
 extern void SHMQueueDelete(SHM_QUEUE *queue);
 extern void SHMQueueInsertBefore(SHM_QUEUE *queue, SHM_QUEUE *elem);
+extern void SHMQueueInsertAfter(SHM_QUEUE *queue, SHM_QUEUE *elem);
 extern Pointer SHMQueueNext(const SHM_QUEUE *queue, const SHM_QUEUE *curElem,
 			 Size linkOffset);
+extern Pointer SHMQueuePrev(const SHM_QUEUE *queue, const SHM_QUEUE *curElem,
+			 Size linkOffset);
 extern bool SHMQueueEmpty(const SHM_QUEUE *queue);
 extern bool SHMQueueIsDetached(const SHM_QUEUE *queue);