com.hazelcast.query.impl

Enum IndexCopyBehavior

java.lang.Object

java.lang.Enum<IndexCopyBehavior>

com.hazelcast.query.impl.IndexCopyBehavior

All Implemented Interfaces:

Serializable, Comparable<IndexCopyBehavior>

public enum IndexCopyBehavior
extends Enum<IndexCopyBehavior>

Defines the behavior for index copying on index read/write. Supported for BINARY and OBJECT in-memory formats. It is also supported for NATIVE in-memory format ONLY in Hazelcast 3.8.7 (and further 3.8.x releases). Why is it needed? In order to support correctness the underlying data structures used by indexes need to do some copying. The copying may take place on-read or on-write: -> Copying on-read means that each index-read operation will copy the result of the query before returning it to the caller. This copying may be expensive, depending on the size of the result, since the result is stored in a map, which means that all entries need to have the hash calculated before being stored in a bucket. Each index-write operation however will be fast, since there will be no copying taking place. -> Copying on-write means that each index-write operation will completely copy the underlying map to provide the copy-on-write semantics. Depending on the index size, it may be a very expensive operation. Each index-read operation will be very fast, however, since it may just access the map and return it to the caller. -> Never copying is tricky. It means that the underlying data structures of the index are concurrently modified without copy-on-write semantics. Index reads never copy the results of a query to a separate map. It means that the results backed by the underlying index-map can change after the query has been executed. Specifically an entry might have been added / removed from an index, or it might have been remapped. Should be used in cases when a the caller expects "mostly correct" results - specifically, if it's ok if some entries returned in the result set do not match the initial query criteria. The fastest solution for read and writes, since no copying takes place. It's a tuneable trade-off - the user may decide.

Enum Constant Summary

Enum Constants

Enum Constant and Description
COPY_ON_READ Underlying data structures of the index are concurrently modified without copy-on-write semantics.
COPY_ON_WRITE Underlying data structures of the index are modified with copy-on-write semantics.
NEVER Underlying data structures of the index are concurrently modified without copy-on-write semantics.

Method Summary

Modifier and Type	Method and Description
static IndexCopyBehavior	valueOf(String name) Returns the enum constant of this type with the specified name.
static IndexCopyBehavior[]	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

COPY_ON_READ

public static final IndexCopyBehavior COPY_ON_READ

Underlying data structures of the index are concurrently modified without copy-on-write semantics. Index queries copy the results of a query on index read to detach the result from the source map. Should be used in index-write intensive cases, since the reads will slow down due to the copying. Default value.

COPY_ON_WRITE

public static final IndexCopyBehavior COPY_ON_WRITE

Underlying data structures of the index are modified with copy-on-write semantics. Previously returned index query results reflect the state of the index at the time of the query and are not affected by future index modifications. Should be used in index-read intensive cases, since the writes will slow down due to the copying.

NEVER

public static final IndexCopyBehavior NEVER

Underlying data structures of the index are concurrently modified without copy-on-write semantics. Index reads never copy the results of a query to a separate map. It means that the results backed by the underlying index-map can change after the query has been executed. Specifically an entry might have been added / removed from an index, or it might have been remapped. Should be used in cases when a the caller expects "mostly correct" results - specifically, if it's ok if some entries returned in the result set do not match the initial query criteria. The fastest solution for read and writes, since no copying takes place.

Method Detail

values

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

Returns:

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

valueOf

public static IndexCopyBehavior 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