org.elasticsearch.index.store

Class Store.MetadataSnapshot

java.lang.Object

org.elasticsearch.index.store.Store.MetadataSnapshot

All Implemented Interfaces:

java.lang.Iterable<StoreFileMetaData>, Writeable

Enclosing class:

Store

public static final class Store.MetadataSnapshot
extends java.lang.Object
implements java.lang.Iterable<StoreFileMetaData>, Writeable

Represents a snapshot of the current directory build from the latest Lucene commit. Only files that are part of the last commit are considered in this datastructure. For backwards compatibility the snapshot might include legacy checksums that are derived from a dedicated checksum file written by older elasticsearch version pre 1.3

Note: This class will ignore the segments.gen file since it's optional and might change concurrently for safety reasons.

See Also:

StoreFileMetaData

Nested Class Summary

Nested classes/interfaces inherited from interface org.elasticsearch.common.io.stream.Writeable

Writeable.Reader<V>, Writeable.Writer<V>

Field Summary

Fields

Modifier and Type	Field and Description
static Store.MetadataSnapshot	EMPTY

Constructor Summary

Constructors

Constructor and Description
MetadataSnapshot(java.util.Map<java.lang.String,StoreFileMetaData> metadata, java.util.Map<java.lang.String,java.lang.String> commitUserData, long numDocs)
MetadataSnapshot(StreamInput in) Read from a stream.

Method Summary

Modifier and Type	Method and Description
java.util.Map<java.lang.String,StoreFileMetaData>	asMap()
boolean	contains(java.lang.String existingFile) Returns true iff this metadata contains the given file.
StoreFileMetaData	get(java.lang.String name)
java.util.Map<java.lang.String,java.lang.String>	getCommitUserData()
long	getNumDocs() Returns the number of documents in this store snapshot
StoreFileMetaData	getSegmentsFile() Returns the segments file that this metadata snapshot represents or null if the snapshot is empty.
java.lang.String	getSyncId() Returns the sync id of the commit point that this MetadataSnapshot represents.
static void	hashFile(org.apache.lucene.util.BytesRefBuilder fileHash, java.io.InputStream in, long size) Computes a strong hash value for small files.
java.util.Iterator<StoreFileMetaData>	iterator()
Store.RecoveryDiff	recoveryDiff(Store.MetadataSnapshot recoveryTargetSnapshot) Returns a diff between the two snapshots that can be used for recovery.
int	size() Returns the number of files in this snapshot
void	writeTo(StreamOutput out) Write this into the StreamOutput.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface java.lang.Iterable

forEach, spliterator

Field Detail

EMPTY

public static final Store.MetadataSnapshot EMPTY

Constructor Detail

MetadataSnapshot

public MetadataSnapshot(java.util.Map<java.lang.String,StoreFileMetaData> metadata,
                        java.util.Map<java.lang.String,java.lang.String> commitUserData,
                        long numDocs)

MetadataSnapshot

public MetadataSnapshot(StreamInput in)
                 throws java.io.IOException

Read from a stream.

Throws:

java.io.IOException

Method Detail

writeTo

public void writeTo(StreamOutput out)
             throws java.io.IOException

Description copied from interface: Writeable

Write this into the StreamOutput.

Specified by:

writeTo in interface Writeable

Throws:

java.io.IOException

getNumDocs

public long getNumDocs()

Returns the number of documents in this store snapshot

hashFile

public static void hashFile(org.apache.lucene.util.BytesRefBuilder fileHash,
                            java.io.InputStream in,
                            long size)
                     throws java.io.IOException

Computes a strong hash value for small files. Note that this method should only be used for files < 1MB

Throws:

java.io.IOException

iterator

public java.util.Iterator<StoreFileMetaData> iterator()

Specified by:

iterator in interface java.lang.Iterable<StoreFileMetaData>

get

public StoreFileMetaData get(java.lang.String name)

asMap

public java.util.Map<java.lang.String,StoreFileMetaData> asMap()

recoveryDiff

public Store.RecoveryDiff recoveryDiff(Store.MetadataSnapshot recoveryTargetSnapshot)

Returns a diff between the two snapshots that can be used for recovery. The given snapshot is treated as the recovery target and this snapshot as the source. The returned diff will hold a list of files that are:

• identical: they exist in both snapshots and they can be considered the same ie. they don't need to be recovered
• different: they exist in both snapshots but their they are not identical
• missing: files that exist in the source but not in the target

This method groups file into per-segment files and per-commit files. A file is treated as identical if and on if all files in it's group are identical. On a per-segment level files for a segment are treated as identical iff:

• all files in this segment have the same checksum
• all files in this segment have the same length
• the segments .si files hashes are byte-identical Note: This is a using a perfect hash function, The metadata transfers the .si file content as it's hash

The .si file contains a lot of diagnostics including a timestamp etc. in the future there might be unique segment identifiers in there hardening this method further.

The per-commit files handles very similar. A commit is composed of the segments_N files as well as generational files like deletes (_x_y.del) or field-info (_x_y.fnm) files. On a per-commit level files for a commit are treated as identical iff:

• all files belonging to this commit have the same checksum
• all files belonging to this commit have the same length
• the segments file segments_N files hashes are byte-identical Note: This is a using a perfect hash function, The metadata transfers the segments_N file content as it's hash

NOTE: this diff will not contain the segments.gen file. This file is omitted on recovery.

size

public int size()

Returns the number of files in this snapshot

getCommitUserData

public java.util.Map<java.lang.String,java.lang.String> getCommitUserData()

contains

public boolean contains(java.lang.String existingFile)

Returns true iff this metadata contains the given file.

getSegmentsFile

public StoreFileMetaData getSegmentsFile()

Returns the segments file that this metadata snapshot represents or null if the snapshot is empty.

getSyncId

public java.lang.String getSyncId()

Returns the sync id of the commit point that this MetadataSnapshot represents.

Returns:

sync id if exists, else null