wal.h File Reference

Write-Ahead Log for the keys and the value positions. More...

#include <stdint.h>
#include <stdio.h>
#include "memtable.h"

Include dependency graph for wal.h:

Go to the source code of this file.

Data Structures
struct	WAL
	Write-Ahead Log(WAL) of the Database. More...

Functions
struct WAL *	WAL_new (char *path)
	Creates a new emtpy WAL.
int	WAL_load_memtable (struct WAL *wal, struct MemTable *memtable)
	Replays the WAL from the start and recreates the MemTable.
int	WAL_append (struct WAL *wal, const char *key, size_t key_len, int64_t value_loc)
	Appends a new MemTable operation to the WAL.
int	WAL_sync (const struct WAL *wal)
	Syncs the WAl to the disk.
void	WAL_free (struct WAL *wal)
	Frees the WAL.

Detailed Description

Write-Ahead Log for the keys and the value positions.

Author

Adam Comer adamb.nosp@m.come.nosp@m.r@gma.nosp@m.il.c.nosp@m.om

Date

May 15, 2020

Copyright

Apache-2.0 License

Function Documentation

WAL_append()

int WAL_append	(	struct WAL *	wal,
		const char *	key,
		size_t	key_len,
		int64_t	value_loc )

Appends a new MemTable operation to the WAL.

For sets, the value_loc should be the position in the ValueLog that the value entry was written to. For deletes, value_loc should be -1 to indicate a tombstone.

Parameters

wal	The WAL to append a MemTable operation to.
key	The key to apply an operation to.
key_len	The length of the key.
value_loc	The location in the ValueLog of the value or -1 if it is being deleted.

Returns

This function returns 0 if the operation was successfully writen to the WAL and -1 if there was an error.

WAL_free()

void WAL_free

(

struct WAL *

wal

)

Frees the WAL.

Note: This function won't delete the file or the underlying data in the WAL. This function only frees the memory allocated to a WAL.

Parameters

wal	The WAL to free.

WAL_load_memtable()

int WAL_load_memtable	(	struct WAL *	wal,
		struct MemTable *	memtable )

Replays the WAL from the start and recreates the MemTable.

This is the main recovery function for the WAL for when the Database restarts.

Parameters

wal	The WAL to replay the log from.
memtable	A empty MemTable to replay the log into.

Returns

This function returns 0 if the WAL successfully replayed and -1 if there was an error.

WAL_new()

struct WAL * WAL_new

(

char *

path

)

Creates a new emtpy WAL.

Note: If a WAL already exists at this path, the file will not be overwritten.

Parameters

path	The path of the new WAL file.

Returns

A pointer to a new WAL.

WAL_sync()

int WAL_sync

(

const struct WAL *

wal

)

Syncs the WAl to the disk.

This function forcefully flushes the changes to the WAL to disk. Use this function sparingly as is will heavily reduce the write throughput of the WAL.

Parameters

wal	The WAL to flush to disk.

Returns

This function returns 0 if the WAL successfully synced to the disk and -1 if there was an error.