func()

in tx.go [345:397]

• 37 lines of code
• 8 McCabe index (conditional complexity)

func (tx *Tx) doCheckpointWAL() {
	if tx.flags.checkpoint {
		return
	}

	// collect page ids that would have an old WAL page
	// entry still alive after this transaction.
	ids := make([]PageID, 0, len(tx.file.wal.mapping))
	walIDS := make([]PageID, 0, len(tx.file.wal.mapping))
	for id, walID := range tx.file.wal.mapping {
		page := tx.pages[id]
		if page != nil {
			if page.flags.dirty {
				// wal pages of dirty pages will be freed on flush -> do not copy
				continue
			}
		}

		ids = append(ids, id)
		walIDS = append(walIDS, walID)
	}

	if len(ids) == 0 {
		return
	}

	// XXX: Some OS/filesystems might lock up when writing to file
	//      from mmapped area.
	//      -> Copy contents into temporary buffer, such that
	//         write operations are not backed by mmapped pages from same file.
	pageSize := int(tx.PageSize())
	writeBuffer := make([]byte, pageSize*len(ids))
	for i := range ids {
		id, walID := ids[i], walIDS[i]

		contents := tx.access(walID)
		if contents == nil {
			panic("invalid WAL mapping")
		}

		tracef("checkpoint copy from WAL page %v -> %v\n", walID, id)

		n := copy(writeBuffer, contents)
		buf := writeBuffer[:n]
		writeBuffer = writeBuffer[n:]

		tx.file.writer.Schedule(tx.writeSync, id, buf)
		tx.freeWALID(id, walID)
	}

	tx.onWALTransfer(len(ids))
	tx.flags.checkpoint = true
}