Hi,
On Tue, Feb 10, 2026 at 01:15:01PM -0500, Andres Freund wrote:
> Hi,
>
> On 2026-02-10 19:14:44 +0200, Heikki Linnakangas wrote:
> Yea, I don't think we need to be perfect here. Just a bit less bad. And, as
> you say, the current order doesn't make a lot of sense.
> Just grouping things like
> - pid, pgxactoff, backendType (i.e. barely if ever changing)
> - wait_event_info, waitStart (i.e. very frequently changing, but typically
> accessed within one proc)
> - sem, lwWaiting, waitLockMode (i.e. stuff that is updated frequently and
> accessed across processes)
With an ordering like in the attached (to apply on top of Heikki's patch), we're
back to 832 bytes.
But, then the pg_attribute_aligned() added in Heikki's patch makes it 896
bytes...
"
/* 816 | 16 */ dlist_node lockGroupLink;
/* XXX 64-byte padding */
/* total size (bytes): 896 */
}
"
What about applying this new ordering and remove the pg_attribute_aligned()? (I
thought the aligned attribute would be smarter than that and not add this 64
padding
bytes).
Regards,
--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
commit ea3aded2c4dec487c8a2ff5470cd7bae83e8dd47
Author: Bertrand Drouvot <[email protected]>
Date: Tue Feb 10 18:54:29 2026 +0000
reorder
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index 53acce8a5a1..5d41301c966 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -184,29 +184,16 @@ typedef enum
*/
typedef struct PGPROC
{
- dlist_node links; /* list link if process is in a
list */
- dlist_head *procgloballist; /* procglobal list that owns this PGPROC */
-
- PGSemaphore sem; /* ONE semaphore to sleep on */
- ProcWaitStatus waitStatus;
-
- Latch procLatch; /* generic latch for process */
-
-
- TransactionId xid; /* id of top-level transaction
currently being
- * executed by
this proc, if running and XID
- * is assigned;
else InvalidTransactionId.
- * mirrored in
ProcGlobal->xids[pgxactoff] */
-
- TransactionId xmin; /* minimal running XID as it
was when we were
- * starting our
xact, excluding LAZY VACUUM:
- * vacuum must
not remove tuples deleted by
- * xid >= xmin
! */
-
int pid; /* Backend's process
ID; 0 if prepared xact */
-
int pgxactoff; /* offset into various
ProcGlobal->arrays with
* data
mirrored from this PGPROC */
+ BackendType backendType; /* what kind of process is this? */
+
+ /* These fields are zero while a backend is still starting up: */
+ Oid databaseId; /* OID of database this
backend is using */
+ Oid roleId; /* OID of role using
this backend */
+ Oid tempNamespaceId; /* OID of temp schema
this backend is
+ *
using */
/*
* Currently running top-level transaction's virtual xid. Together these
@@ -227,24 +214,44 @@ typedef struct PGPROC
*
InvalidLocalTransactionId */
} vxid;
- /* These fields are zero while a backend is still starting up: */
- Oid databaseId; /* OID of database this
backend is using */
- Oid roleId; /* OID of role using
this backend */
+ dlist_node links; /* list link if process is in a
list */
+ dlist_head *procgloballist; /* procglobal list that owns this PGPROC */
- Oid tempNamespaceId; /* OID of temp schema
this backend is
- *
using */
+ uint32 wait_event_info; /* proc's wait information */
+ pg_atomic_uint64 waitStart; /* time at which wait for lock acquisition
+ * started */
- BackendType backendType; /* what kind of process is this? */
+ TransactionId xid; /* id of top-level transaction
currently being
+ * executed by
this proc, if running and XID
+ * is assigned;
else InvalidTransactionId.
+ * mirrored in
ProcGlobal->xids[pgxactoff] */
- /*
- * While in hot standby mode, shows that a conflict signal has been sent
- * for the current transaction. Set/cleared while holding ProcArrayLock,
- * though not required. Accessed without lock, if needed.
- *
- * This is a bitmask; each bit corresponds to a RecoveryConflictReason
- * enum value.
- */
- pg_atomic_uint32 pendingRecoveryConflicts;
+ TransactionId xmin; /* minimal running XID as it
was when we were
+ * starting our
xact, excluding LAZY VACUUM:
+ * vacuum must
not remove tuples deleted by
+ * xid >= xmin
! */
+
+ ProcWaitStatus waitStatus;
+ int delayChkptFlags; /* for DELAY_CHKPT_*
flags */
+
+ LOCKMODE waitLockMode; /* type of lock we're waiting for */
+ LOCKMASK heldLocks; /* bitmask for lock types
already held on this
+ * lock object
by this backend */
+
+ uint8 statusFlags; /* this backend's status flags, see
PROC_*
+ * above.
mirrored in
+ *
ProcGlobal->statusFlags[pgxactoff] */
+ XidCacheStatus subxidStatus; /* mirrored with
+ *
ProcGlobal->subxidStates[i] */
+
+ bool procArrayGroupMember; /* true, if member of ProcArray
group
+
* waiting for XID clear */
+ bool clogGroupMember; /* true, if member of clog
group */
+ bool fpVXIDLock; /* are we holding a fast-path
VXID lock? */
+
+ LocalTransactionId fpLocalTransactionId; /* lxid for fast-path
VXID
+
* lock */
+ PGSemaphore sem; /* ONE semaphore to sleep on */
/*
* Info about LWLock the process is currently waiting for, if any.
@@ -255,6 +262,19 @@ typedef struct PGPROC
*/
uint8 lwWaiting; /* see LWLockWaitState */
uint8 lwWaitMode; /* lwlock mode being waited for
*/
+
+ Latch procLatch; /* generic latch for process */
+
+ /*
+ * While in hot standby mode, shows that a conflict signal has been sent
+ * for the current transaction. Set/cleared while holding ProcArrayLock,
+ * though not required. Accessed without lock, if needed.
+ *
+ * This is a bitmask; each bit corresponds to a RecoveryConflictReason
+ * enum value.
+ */
+ pg_atomic_uint32 pendingRecoveryConflicts;
+
proclist_node lwWaitLink; /* position in LW lock wait list */
/* Support for condition variables. */
@@ -264,17 +284,6 @@ typedef struct PGPROC
/* waitLock and waitProcLock are NULL if not currently waiting. */
LOCK *waitLock; /* Lock object we're sleeping on ... */
PROCLOCK *waitProcLock; /* Per-holder info for awaited lock */
- LOCKMODE waitLockMode; /* type of lock we're waiting for */
- LOCKMASK heldLocks; /* bitmask for lock types
already held on this
- * lock object
by this backend */
- pg_atomic_uint64 waitStart; /* time at which wait for lock acquisition
- * started */
-
- int delayChkptFlags; /* for DELAY_CHKPT_*
flags */
-
- uint8 statusFlags; /* this backend's status flags, see
PROC_*
- * above.
mirrored in
- *
ProcGlobal->statusFlags[pgxactoff] */
/*
* Info to allow us to wait for synchronous replication, if needed.
@@ -293,15 +302,11 @@ typedef struct PGPROC
*/
dlist_head myProcLocks[NUM_LOCK_PARTITIONS];
- XidCacheStatus subxidStatus; /* mirrored with
- *
ProcGlobal->subxidStates[i] */
struct XidCache subxids; /* cache for subtransaction XIDs */
/* Support for group XID clearing. */
- /* true, if member of ProcArray group waiting for XID clear */
- bool procArrayGroupMember;
- /* next ProcArray group member waiting for XID clear */
- pg_atomic_uint32 procArrayGroupNext;
+ pg_atomic_uint32 procArrayGroupNext; /* next ProcArray group member
+
* waiting for XID clear */
/*
* latest transaction id among the transaction's main XID and
@@ -309,10 +314,7 @@ typedef struct PGPROC
*/
TransactionId procArrayGroupMemberXid;
- uint32 wait_event_info; /* proc's wait information */
-
/* Support for group transaction status update. */
- bool clogGroupMember; /* true, if member of clog
group */
pg_atomic_uint32 clogGroupNext; /* next clog group member */
TransactionId clogGroupMemberXid; /* transaction id of clog group
member */
XidStatus clogGroupMemberXidStatus; /* transaction status
of clog
@@ -326,9 +328,6 @@ typedef struct PGPROC
LWLock fpInfoLock; /* protects per-backend
fast-path state */
uint64 *fpLockBits; /* lock modes held for each fast-path
slot */
Oid *fpRelId; /* slots for rel oids */
- bool fpVXIDLock; /* are we holding a fast-path
VXID lock? */
- LocalTransactionId fpLocalTransactionId; /* lxid for fast-path
VXID
-
* lock */
/*
* Support for lock groups. Use LockHashPartitionLockByProc on the
group
