io.atomix.copycat.server.storage

Enum StorageLevel

java.lang.Object

java.lang.Enum<StorageLevel>

io.atomix.copycat.server.storage.StorageLevel

All Implemented Interfaces:

Serializable, Comparable<StorageLevel>

public enum StorageLevel
extends Enum<StorageLevel>

Log storage level configuration values which control how logs are stored on disk or in memory.

Storage levels represent the method used to store the individual segments that make up a Log. When configuring a Storage module, the storage can be configured to write entries to disk, memory, or memory-mapped files using the values provided by this enum. The StorageLevel configuration dictates the type of Buffer to which to write entries. See the specific storage levels for more information.

Author:

See Also:

Storage

Enum Constant Summary

Enum Constants

Enum Constant and Description
DISK Stores logs on disk.
MAPPED Stores logs in memory mapped files.
MEMORY Stores logs in memory only.

Method Summary

Modifier and Type	Method and Description
static StorageLevel	valueOf(String name) Returns the enum constant of this type with the specified name.
static StorageLevel[]	values() Returns an array containing the constants of this enum type, in the order they are declared.

Methods inherited from class java.lang.Enum

compareTo, equals, getDeclaringClass, hashCode, name, ordinal, toString, valueOf

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Enum Constant Detail

MEMORY

public static final StorageLevel MEMORY

Stores logs in memory only.

In-memory logs will be written to segments backed by HeapBuffer. Each MEMORY segment may only store up to 2^32-1 bytes. Entries written to in-memory logs are not recoverable after a crash. If your use case requires strong persistence, use DISK or MAPPED storage.

MAPPED

public static final StorageLevel MAPPED

Stores logs in memory mapped files.

Memory mapped logs will be written to segments backed by MappedBuffer. Entries written to memory mapped files may be recovered after a crash, but the MAPPED storage level does not guarantee that all entries written to the log will be persisted. Additionally, the use of persistent storage levels reduces the amount of overhead required to catch the log up at startup.

DISK

public static final StorageLevel DISK

Stores logs on disk.

On-disk logs will be written to segments backed by FileBuffer, which in turn is backed by RandomAccessFile. Entries written to DISK storage can be recovered in the event of a failure or other restart. Additionally, the use of persistent storage levels reduces the amount of overhead required to catch the log up at startup.

Method Detail

values

public static StorageLevel[] values()

Returns an array containing the constants of this enum type, in the order they are declared. This method may be used to iterate over the constants as follows:

for (StorageLevel c : StorageLevel.values())
    System.out.println(c);

Returns:

an array containing the constants of this enum type, in the order they are declared

valueOf

public static StorageLevel valueOf(String name)

Returns the enum constant of this type with the specified name. The string must match exactly an identifier used to declare an enum constant in this type. (Extraneous whitespace characters are not permitted.)

Parameters:

name - the name of the enum constant to be returned.

Returns:

the enum constant with the specified name

Throws:

IllegalArgumentException - if this enum type has no constant with the specified name

NullPointerException - if the argument is null