Function pgstat_send_wal

src/backend/postmaster/pgstat.c:3363–3446

---------- * pgstat_send_wal() - * * Send WAL statistics to the collector. * * If 'force' is not set, WAL stats message is only sent if enough time has * passed since last one was sent to reach PGSTAT_STAT_INTERVAL. * ---------- */

 * ----------
 */
void
pgstat_send_wal(bool force)
{
	static TimestampTz sendTime = 0;

	/*
	 * This function can be called even if nothing at all has happened. In
	 * this case, avoid sending a completely empty message to the stats
	 * collector.
	 *
	 * Check wal_records counter to determine whether any WAL activity has
	 * happened since last time. Note that other WalUsage counters don't need
	 * to be checked because they are incremented always together with
	 * wal_records counter.
	 *
	 * m_wal_buffers_full also doesn't need to be checked because it's
	 * incremented only when at least one WAL record is generated (i.e.,
	 * wal_records counter is incremented). But for safely, we assert that
	 * m_wal_buffers_full is always zero when no WAL record is generated
	 *
	 * This function can be called by a process like walwriter that normally
	 * generates no WAL records. To determine whether any WAL activity has
	 * happened at that process since the last time, the numbers of WAL writes
	 * and syncs are also checked.
	 */
	if (pgWalUsage.wal_records == prevWalUsage.wal_records &&
		WalStats.m_wal_write == 0 && WalStats.m_wal_sync == 0)
	{
		Assert(WalStats.m_wal_buffers_full == 0);
		return;
	}

	if (!force)
	{
		TimestampTz now = GetCurrentTimestamp();

		/*
		 * Don't send a message unless it's been at least PGSTAT_STAT_INTERVAL
		 * msec since we last sent one to avoid overloading the stats
		 * collector.
		 */
		if (!TimestampDifferenceExceeds(sendTime, now, PGSTAT_STAT_INTERVAL))
			return;
		sendTime = now;
	}

	/*
	 * Set the counters related to generated WAL data if the counters were
	 * updated.
	 */
	if (pgWalUsage.wal_records != prevWalUsage.wal_records)
	{
		WalUsage	walusage;

		/*
		 * Calculate how much WAL usage counters were increased by
		 * substracting the previous counters from the current ones. Fill the
		 * results in WAL stats message.