From ab355e3a88de745607f6dd4c21f0119b5c68f2ad Mon Sep 17 00:00:00 2001 From: Heikki Linnakangas Date: Sun, 3 Mar 2024 19:37:28 +0200 Subject: Redefine backend ID to be an index into the proc array Previously, backend ID was an index into the ProcState array, in the shared cache invalidation manager (sinvaladt.c). The entry in the ProcState array was reserved at backend startup by scanning the array for a free entry, and that was also when the backend got its backend ID. Things become slightly simpler if we redefine backend ID to be the index into the PGPROC array, and directly use it also as an index to the ProcState array. This uses a little more memory, as we reserve a few extra slots in the ProcState array for aux processes that don't need them, but the simplicity is worth it. Aux processes now also have a backend ID. This simplifies the reservation of BackendStatusArray and ProcSignal slots. You can now convert a backend ID into an index into the PGPROC array simply by subtracting 1. We still use 0-based "pgprocnos" in various places, for indexes into the PGPROC array, but the only difference now is that backend IDs start at 1 while pgprocnos start at 0. (The next commmit will get rid of the term "backend ID" altogether and make everything 0-based.) There is still a 'backendId' field in PGPROC, now part of 'vxid' which encapsulates the backend ID and local transaction ID together. It's needed for prepared xacts. For regular backends, the backendId is always equal to pgprocno + 1, but for prepared xact PGPROC entries, it's the ID of the original backend that processed the transaction. Reviewed-by: Andres Freund, Reid Thompson Discussion: https://www.postgresql.org/message-id/8171f1aa-496f-46a6-afc3-c46fe7a9b407@iki.fi --- src/backend/utils/adt/mcxtfuncs.c | 14 ++++---------- 1 file changed, 4 insertions(+), 10 deletions(-) (limited to 'src/backend/utils/adt/mcxtfuncs.c') diff --git a/src/backend/utils/adt/mcxtfuncs.c b/src/backend/utils/adt/mcxtfuncs.c index 4708d73f5fa..a7267dc15d1 100644 --- a/src/backend/utils/adt/mcxtfuncs.c +++ b/src/backend/utils/adt/mcxtfuncs.c @@ -148,19 +148,11 @@ pg_log_backend_memory_contexts(PG_FUNCTION_ARGS) PGPROC *proc; BackendId backendId = InvalidBackendId; - proc = BackendPidGetProc(pid); - /* * See if the process with given pid is a backend or an auxiliary process. - * - * If the given process is a backend, use its backend id in - * SendProcSignal() later to speed up the operation. Otherwise, don't do - * that because auxiliary processes (except the startup process) don't - * have a valid backend id. */ - if (proc != NULL) - backendId = proc->backendId; - else + proc = BackendPidGetProc(pid); + if (proc == NULL) proc = AuxiliaryPidGetProc(pid); /* @@ -183,6 +175,8 @@ pg_log_backend_memory_contexts(PG_FUNCTION_ARGS) PG_RETURN_BOOL(false); } + if (proc != NULL) + backendId = GetBackendIdFromPGProc(proc); if (SendProcSignal(pid, PROCSIG_LOG_MEMORY_CONTEXT, backendId) < 0) { /* Again, just a warning to allow loops */ -- cgit v1.2.3