Replace BackendIds with 0-based ProcNumbers

Now that BackendId was just another index into the proc array, it was
redundant with the 0-based proc numbers used in other places. Replace
all usage of backend IDs with proc numbers.

The only place where the term "backend id" remains is in a few pgstat
functions that expose backend IDs at the SQL level. Those IDs are now
in fact 0-based ProcNumbers too, but the documentation still calls
them "backend ids". That term still seems appropriate to describe what
the numbers are, so I let it be.

One user-visible effect is that pg_temp_0 is now a valid temp schema
name, for backend with ProcNumber 0.

Reviewed-by: Andres Freund
Discussion: https://www.postgresql.org/message-id/8171f1aa-496f-46a6-afc3-c46fe7a9b407@iki.fi

2 files changed, 14 insertions, 14 deletions

diff --git a/src/backend/postmaster/pgarch.c b/src/backend/postmaster/pgarch.c
index 04fedfae2fa..bb0eb13a898 100644
--- a/src/backend/postmaster/pgarch.c
+++ b/src/backend/postmaster/pgarch.c
@@ -79,7 +79,7 @@
 /* Shared memory area for archiver process */
 typedef struct PgArchData
 {
-	int			pgprocno;		/* pgprocno of archiver process */
+	int			pgprocno;		/* proc number of archiver process */
 
 	/*
 	 * Forces a directory scan in pgarch_readyXlog().
@@ -170,7 +170,7 @@ PgArchShmemInit(void)
 	{
 		/* First time through, so initialize */
 		MemSet(PgArch, 0, PgArchShmemSize());
-		PgArch->pgprocno = INVALID_PGPROCNO;
+		PgArch->pgprocno = INVALID_PROC_NUMBER;
 		pg_atomic_init_u32(&PgArch->force_dir_scan, 0);
 	}
 }
@@ -236,8 +236,8 @@ PgArchiverMain(void)
 	on_shmem_exit(pgarch_die, 0);
 
 	/*
-	 * Advertise our pgprocno so that backends can use our latch to wake us up
-	 * while we're sleeping.
+	 * Advertise our proc number so that backends can use our latch to wake us
+	 * up while we're sleeping.
 	 */
 	PgArch->pgprocno = MyProcNumber;
 
@@ -271,7 +271,7 @@ PgArchWakeup(void)
 	 * process' (or no process') latch.  Even in that case the archiver will
 	 * be relaunched shortly and will start archiving.
 	 */
-	if (arch_pgprocno != INVALID_PGPROCNO)
+	if (arch_pgprocno != INVALID_PROC_NUMBER)
 		SetLatch(&ProcGlobal->allProcs[arch_pgprocno].procLatch);
 }
 
@@ -741,7 +741,7 @@ pgarch_archiveDone(char *xlog)
 static void
 pgarch_die(int code, Datum arg)
 {
-	PgArch->pgprocno = INVALID_PGPROCNO;
+	PgArch->pgprocno = INVALID_PROC_NUMBER;
 }
 
 /*
diff --git a/src/backend/postmaster/walsummarizer.c b/src/backend/postmaster/walsummarizer.c
index f295eff32f4..8636d9424ec 100644
--- a/src/backend/postmaster/walsummarizer.c
+++ b/src/backend/postmaster/walsummarizer.c
@@ -71,8 +71,8 @@ typedef struct
 	 * and so the LSN might point to the start of the next file even though
 	 * that might happen to be in the middle of a WAL record.
 	 *
-	 * summarizer_pgprocno is the pgprocno value for the summarizer process,
-	 * if one is running, or else INVALID_PGPROCNO.
+	 * summarizer_pgprocno is the proc number of the summarizer process, if
+	 * one is running, or else INVALID_PROC_NUMBER.
 	 *
 	 * pending_lsn is used by the summarizer to advertise the ending LSN of a
 	 * record it has recently read. It shouldn't ever be less than
@@ -83,7 +83,7 @@ typedef struct
 	TimeLineID	summarized_tli;
 	XLogRecPtr	summarized_lsn;
 	bool		lsn_is_exact;
-	int			summarizer_pgprocno;
+	ProcNumber	summarizer_pgprocno;
 	XLogRecPtr	pending_lsn;
 
 	/*
@@ -195,7 +195,7 @@ WalSummarizerShmemInit(void)
 		WalSummarizerCtl->summarized_tli = 0;
 		WalSummarizerCtl->summarized_lsn = InvalidXLogRecPtr;
 		WalSummarizerCtl->lsn_is_exact = false;
-		WalSummarizerCtl->summarizer_pgprocno = INVALID_PGPROCNO;
+		WalSummarizerCtl->summarizer_pgprocno = INVALID_PROC_NUMBER;
 		WalSummarizerCtl->pending_lsn = InvalidXLogRecPtr;
 		ConditionVariableInit(&WalSummarizerCtl->summary_file_cv);
 	}
@@ -444,7 +444,7 @@ GetWalSummarizerState(TimeLineID *summarized_tli, XLogRecPtr *summarized_lsn,
 
 		*summarized_tli = WalSummarizerCtl->summarized_tli;
 		*summarized_lsn = WalSummarizerCtl->summarized_lsn;
-		if (summarizer_pgprocno == INVALID_PGPROCNO)
+		if (summarizer_pgprocno == INVALID_PROC_NUMBER)
 		{
 			/*
 			 * If the summarizer has exited, the fact that it had processed
@@ -613,7 +613,7 @@ GetOldestUnsummarizedLSN(TimeLineID *tli, bool *lsn_is_exact,
 void
 SetWalSummarizerLatch(void)
 {
-	int			pgprocno;
+	ProcNumber	pgprocno;
 
 	if (WalSummarizerCtl == NULL)
 		return;
@@ -622,7 +622,7 @@ SetWalSummarizerLatch(void)
 	pgprocno = WalSummarizerCtl->summarizer_pgprocno;
 	LWLockRelease(WALSummarizerLock);
 
-	if (pgprocno != INVALID_PGPROCNO)
+	if (pgprocno != INVALID_PROC_NUMBER)
 		SetLatch(&ProcGlobal->allProcs[pgprocno].procLatch);
 }
 
@@ -683,7 +683,7 @@ static void
 WalSummarizerShutdown(int code, Datum arg)
 {
 	LWLockAcquire(WALSummarizerLock, LW_EXCLUSIVE);
-	WalSummarizerCtl->summarizer_pgprocno = INVALID_PGPROCNO;
+	WalSummarizerCtl->summarizer_pgprocno = INVALID_PROC_NUMBER;
 	LWLockRelease(WALSummarizerLock);
 }