Function MarkBufferDirty

src/backend/storage/buffer/bufmgr.c:1680–1728

* MarkBufferDirty * * Marks buffer contents as dirty (actual write happens later). * * Buffer must be pinned and exclusive-locked. (If caller does not hold * exclusive lock, then somebody could be in process of writing the buffer, * leading to risk of bad data written to disk.) */

 * leading to risk of bad data written to disk.)
 */
void
MarkBufferDirty(Buffer buffer)
{
	BufferDesc *bufHdr;
	uint32		buf_state;
	uint32		old_buf_state;

	if (!BufferIsValid(buffer))
		elog(ERROR, "bad buffer ID: %d", buffer);

	if (BufferIsLocal(buffer))
	{
		MarkLocalBufferDirty(buffer);
		return;
	}

	bufHdr = GetBufferDescriptor(buffer - 1);

	Assert(BufferIsPinned(buffer));
	Assert(LWLockHeldByMeInMode(BufferDescriptorGetContentLock(bufHdr),
								LW_EXCLUSIVE));

	old_buf_state = pg_atomic_read_u32(&bufHdr->state);
	for (;;)
	{
		if (old_buf_state & BM_LOCKED)
			old_buf_state = WaitBufHdrUnlocked(bufHdr);

		buf_state = old_buf_state;

		Assert(BUF_STATE_GET_REFCOUNT(buf_state) > 0);
		buf_state |= BM_DIRTY | BM_JUST_DIRTIED;

		if (pg_atomic_compare_exchange_u32(&bufHdr->state, &old_buf_state,
										   buf_state))
			break;
	}

	/*
	 * If the buffer was not dirty already, do vacuum accounting.
	 */
	if (!(old_buf_state & BM_DIRTY))
	{
		VacuumPageDirty++;
		pgBufferUsage.shared_blks_dirtied++;
		if (VacuumCostActive)
			VacuumCostBalance += VacuumCostPageDirty;
	}
}

/*
 * ReleaseAndReadBuffer -- combine ReleaseBuffer() and ReadBuffer()