Package org.apache.cassandra.index.sai.disk.v1.keystore

Class KeyLookup

java.lang.Object

org.apache.cassandra.index.sai.disk.v1.keystore.KeyLookup

@NotThreadSafe
public class KeyLookup
extends Object

Provides read access to an on-disk sequence of partition or clustering keys written by KeyStoreWriter.

Care has been taken to make this structure as efficient as possible. Reading keys does not require allocating data heap buffers per each read operation. Only one key at a time is loaded to memory. Low complexity algorithms are used – a lookup of the key by point id is constant time, and a lookup of the point id by the key is logarithmic.

Because the blocks are prefix compressed, random access applies only to the locating the whole block. In order to jump to a concrete key inside the block, the block keys are iterated from the block beginning.

See Also:

• KeyStoreWriter

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
class	KeyLookup.Cursor	Allows reading the keys from the keys file.

Field Summary

Fields

Modifier and Type	Field	Description
static final String	INDEX_OUT_OF_BOUNDS

Constructor Summary

Constructors

Constructor	Description
KeyLookup(FileHandle keysFileHandle, FileHandle keysBlockOffsets, KeyLookupMeta keyLookupMeta, NumericValuesMeta keyBlockOffsetsMeta)	Creates a new reader based on its data components.

Method Summary

Modifier and Type	Method	Description
KeyLookup.Cursor	openCursor()	Opens a cursor over the keys stored in the keys file.

Methods inherited from class java.lang.Object

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

Field Details

INDEX_OUT_OF_BOUNDS

public static final String INDEX_OUT_OF_BOUNDS

See Also:

• Constant Field Values

Constructor Details

KeyLookup

public KeyLookup(@Nonnull
 FileHandle keysFileHandle,
 @Nonnull
 FileHandle keysBlockOffsets,
 @Nonnull
 KeyLookupMeta keyLookupMeta,
 @Nonnull
 NumericValuesMeta keyBlockOffsetsMeta)
          throws IOException

Creates a new reader based on its data components.

It does not own the components, so you must close them separately after you're done with the reader.

Parameters:

keysFileHandle - handle to the file with a sequence of prefix-compressed blocks each storing a fixed number of keys

keysBlockOffsets - handle to the file containing an encoded sequence of the file offsets pointing to the blocks

keyLookupMeta - metadata object created earlier by the writer

keyBlockOffsetsMeta - metadata object for the block offsets

Throws:

IOException

Method Details

openCursor

@Nonnull
public KeyLookup.Cursor openCursor()
                            throws IOException

Opens a cursor over the keys stored in the keys file.

This will read the first key into the key buffer and point to the first point in the keys file.

The cursor is to be used in a single thread. The cursor is valid as long this object hasn't been closed. You must close the cursor when you no longer need it.

Throws:

IOException