Change GetMultiXactInfo() to return the next multixact offset

This routine returned a number of members as a MultiXactOffset,
calculated based on the difference between the next-to-be-assigned
offset and the oldest offset.  However, this number is not actually an
offset but a number.

This type confusion comes from the original implementation of
MultiXactMemberFreezeThreshold(), in 53bb309d2d5a.  The number of
members is now defined as a uint64, large enough for MultiXactOffset.
This change will be used in a follow-up patch.

Reviewed-by: Naga Appani <nagnrik@gmail.com>
Discussion: https://postgr.es/m/aUyTvZMq2CLgNEB4@paquier.xyz

diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c
index 34956a5a6634a82194a1127b3bf67fac4a55ee75..0d6f594e2a06c513881719e8152343d6e5dba13e 100644 (file)
--- a/src/backend/access/transam/multixact.c
+++ b/src/backend/access/transam/multixact.c
@@ -2461,25 +2461,23 @@ find_multixact_start(MultiXactId multi, MultiXactOffset *result)
  *
  * Returns information about the current MultiXact state, as of:
  * multixacts: Number of MultiXacts (nextMultiXactId - oldestMultiXactId)
- * members: Number of member entries (nextOffset - oldestOffset)
+ * nextOffset: Next-to-be-assigned offset
  * oldestMultiXactId: Oldest MultiXact ID still in use
  * oldestOffset: Oldest offset still in use
  */
 void
-GetMultiXactInfo(uint32 *multixacts, MultiXactOffset *members,
+GetMultiXactInfo(uint32 *multixacts, MultiXactOffset *nextOffset,
                                 MultiXactId *oldestMultiXactId, MultiXactOffset *oldestOffset)
 {
-       MultiXactOffset nextOffset;
        MultiXactId nextMultiXactId;
 
        LWLockAcquire(MultiXactGenLock, LW_SHARED);
-       nextOffset = MultiXactState->nextOffset;
+       *nextOffset = MultiXactState->nextOffset;
        *oldestMultiXactId = MultiXactState->oldestMultiXactId;
        nextMultiXactId = MultiXactState->nextMXact;
        *oldestOffset = MultiXactState->oldestOffset;
        LWLockRelease(MultiXactGenLock);
 
-       *members = nextOffset - *oldestOffset;
        *multixacts = nextMultiXactId - *oldestMultiXactId;
 }
 
@@ -2514,16 +2512,18 @@ GetMultiXactInfo(uint32 *multixacts, MultiXactOffset *members,
 int
 MultiXactMemberFreezeThreshold(void)
 {
-       MultiXactOffset members;
        uint32          multixacts;
        uint32          victim_multixacts;
        double          fraction;
        int                     result;
        MultiXactId oldestMultiXactId;
        MultiXactOffset oldestOffset;
+       MultiXactOffset nextOffset;
+       uint64          members;
 
-       /* Read the current offsets and members usage. */
-       GetMultiXactInfo(&multixacts, &members, &oldestMultiXactId, &oldestOffset);
+       /* Read the current offsets and multixact usage. */
+       GetMultiXactInfo(&multixacts, &nextOffset, &oldestMultiXactId, &oldestOffset);
+       members = nextOffset - oldestOffset;
 
        /* If member space utilization is low, no special action is required. */
        if (members <= MULTIXACT_MEMBER_LOW_THRESHOLD)

diff --git a/src/include/access/multixact.h b/src/include/access/multixact.h
index 6433fe163641ea1d9e434af86f6753e4811afefa..d22abbb72512943b8b2c6989c37b3fa052e0749c 100644 (file)
--- a/src/include/access/multixact.h
+++ b/src/include/access/multixact.h
@@ -109,7 +109,7 @@ extern bool MultiXactIdIsRunning(MultiXactId multi, bool isLockOnly);
 extern void MultiXactIdSetOldestMember(void);
 extern int     GetMultiXactIdMembers(MultiXactId multi, MultiXactMember **members,
                                                                  bool from_pgupgrade, bool isLockOnly);
-extern void GetMultiXactInfo(uint32 *multixacts, MultiXactOffset *members,
+extern void GetMultiXactInfo(uint32 *multixacts, MultiXactOffset *nextOffset,
                                                         MultiXactId *oldestMultiXactId,
                                                         MultiXactOffset *oldestOffset);
 extern bool MultiXactIdPrecedes(MultiXactId multi1, MultiXactId multi2);