org.rocksdb

Enum IndexShorteningMode

java.lang.Object

java.lang.Enum<IndexShorteningMode>

org.rocksdb.IndexShorteningMode

All Implemented Interfaces:

java.io.Serializable, java.lang.Comparable<IndexShorteningMode>

public enum IndexShorteningMode
extends java.lang.Enum<IndexShorteningMode>

This enum allows trading off increased index size for improved iterator seek performance in some situations, particularly when block cache is disabled (ReadOptions.fillCache() == false and direct IO is enabled (DBOptions.useDirectReads() == true). The default mode is the best tradeoff for most use cases. This option only affects newly written tables. The index contains a key separating each pair of consecutive blocks. Let A be the highest key in one block, B the lowest key in the next block, and I the index entry separating these two blocks: [ ... A] I [B ...] I is allowed to be anywhere in [A, B). If an iterator is seeked to a key in (A, I], we'll unnecessarily read the first block, then immediately fall through to the second block. However, if I=A, this can't happen, and we'll read only the second block. In kNoShortening mode, we use I=A. In other modes, we use the shortest key in [A, B), which usually significantly reduces index size. There's a similar story for the last index entry, which is an upper bound of the highest key in the file. If it's shortened and therefore overestimated, iterator is likely to unnecessarily read the last data block from each file on each seek.

Enum Constant Summary

Enum Constants

Enum Constant and Description
kNoShortening Use full keys.
kShortenSeparators Shorten index keys between blocks, but use full key for the last index key, which is the upper bound of the whole file.
kShortenSeparatorsAndSuccessor Shorten both keys between blocks and key after last block.

Method Summary

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

Methods inherited from class java.lang.Enum

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

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Enum Constant Detail

kNoShortening

public static final IndexShorteningMode kNoShortening

Use full keys.

kShortenSeparators

public static final IndexShorteningMode kShortenSeparators

Shorten index keys between blocks, but use full key for the last index key, which is the upper bound of the whole file.

kShortenSeparatorsAndSuccessor

public static final IndexShorteningMode kShortenSeparatorsAndSuccessor

Shorten both keys between blocks and key after last block.

Method Detail

values

public static IndexShorteningMode[] 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 (IndexShorteningMode c : IndexShorteningMode.values())
    System.out.println(c);

Returns:

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

valueOf

public static IndexShorteningMode valueOf(java.lang.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:

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

java.lang.NullPointerException - if the argument is null