PostgreSQLのレプリケーション関連の関数についてメモ

/* Shared memory area for management of walreceiver process */
typedef struct
{
//…(略)…
	/*
	 * receiveStart and receiveStartTLI indicate the first byte position and
	 * timeline that will be received. When startup process starts the
	 * walreceiver, it sets these to the point where it wants the streaming to
	 * begin.
	 */
	XLogRecPtr	receiveStart;
	TimeLineID	receiveStartTLI;

	/*
	 * flushedUpto-1 is the last byte position that has already been received,
	 * and receivedTLI is the timeline it came from.  At the first startup of
	 * walreceiver, these are set to receiveStart and receiveStartTLI. After
	 * that, walreceiver updates these whenever it flushes the received WAL to
	 * disk.
	 */
	XLogRecPtr	flushedUpto;
	TimeLineID	receivedTLI;
//…(略)…
} WalRcvData;

/*
 * Shared-memory state for WAL recovery.
 */
typedef struct XLogRecoveryCtlData
//…(略)…
	/*
	 * Last record successfully replayed.
	 */
	XLogRecPtr	lastReplayedReadRecPtr; /* start position */
	XLogRecPtr	lastReplayedEndRecPtr;	/* end+1 position */
	TimeLineID	lastReplayedTLI;	/* timeline */

/*
 * Shared state data for WAL insertion.
 */
typedef struct XLogCtlInsert
//…(略)…
	/*
	 * CurrBytePos is the end of reserved WAL. The next record will be
	 * inserted at that position. PrevBytePos is the start position of the
	 * previously inserted (or rather, reserved) record - it is copied to the
	 * prev-link of the next record. These are stored as "usable byte
	 * positions" rather than XLogRecPtrs (see XLogBytePosToRecPtr()).
	 */
	uint64		CurrBytePos;
	uint64		PrevBytePos;

/*
 * Total shared-memory state for XLOG.
 */
typedef struct XLogCtlData
//…(略)…
	/*
	 * Protected by info_lck and WALWriteLock (you must hold either lock to
	 * read it, but both to update)
	 */
	XLogwrtResult LogwrtResult;

typedef struct XLogwrtResult
{
	XLogRecPtr	Write;			/* last byte + 1 written out */
	XLogRecPtr	Flush;			/* last byte + 1 flushed */
} XLogwrtResult;

/*
 * Returns activity of walsenders, including pids and xlog locations sent to
 * standby servers.
 */
Datum
pg_stat_get_wal_senders(PG_FUNCTION_ARGS)
{
//…(略)…
	for (i = 0; i < max_wal_senders; i++)
	{
		WalSnd	   *walsnd = &WalSndCtl->walsnds[i];
		XLogRecPtr	sentPtr;
		XLogRecPtr	write;
		XLogRecPtr	flush;
		XLogRecPtr	apply;
//…(略)…
		sentPtr = walsnd->sentPtr;
		state = walsnd->state;
		write = walsnd->write;
		flush = walsnd->flush;
		apply = walsnd->apply;

/*
 * Each walsender has a WalSnd struct in shared memory.
 *
 * This struct is protected by its 'mutex' spinlock field, except that some
 * members are only written by the walsender process itself, and thus that
 * process is free to read those members without holding spinlock.  pid and
 * needreload always require the spinlock to be held for all accesses.
 */
typedef struct WalSnd
//…(略)…
	/*
	 * The xlog locations that have been written, flushed, and applied by
	 * standby-side. These may be invalid if the standby-side has not offered
	 * values yet.
	 */
	XLogRecPtr	write;
	XLogRecPtr	flush;
	XLogRecPtr	apply;

/*
 * Returns activity of WAL receiver, including pid, state and xlog locations
 * received from the WAL sender of another server.
 */
Datum
pg_stat_get_wal_receiver(PG_FUNCTION_ARGS)
//…(略)…
	receive_start_lsn = WalRcv->receiveStart;
	receive_start_tli = WalRcv->receiveStartTLI;
	flushed_lsn = WalRcv->flushedUpto;
	received_tli = WalRcv->receivedTLI;