org.apache.hadoop.hbase.regionserver

Class NonLazyKeyValueScanner

java.lang.Object

org.apache.hadoop.hbase.regionserver.NonLazyKeyValueScanner

All Implemented Interfaces:

KeyValueScanner

Direct Known Subclasses:

MemStore.MemStoreScanner, NonReversedNonLazyKeyValueScanner

@InterfaceAudience.Private
public abstract class NonLazyKeyValueScanner
extends Object
implements KeyValueScanner

A "non-lazy" scanner which always does a real seek operation. Most scanners are inherited from this class.

Constructor Summary

Constructors

Constructor and Description
NonLazyKeyValueScanner()

Method Summary

Methods

Modifier and Type	Method and Description
static boolean	doRealSeek(KeyValueScanner scanner, KeyValue kv, boolean forward)
void	enforceSeek() Does the real seek operation in case it was skipped by seekToRowCol(KeyValue, boolean) (TODO: Whats this?).
boolean	isFileScanner()
boolean	realSeekDone() We optimize our store scanners by checking the most recent store file first, so we sometimes pretend we have done a seek but delay it until the store scanner bubbles up to the top of the key-value heap.
boolean	requestSeek(KeyValue kv, boolean forward, boolean useBloom) Similar to KeyValueScanner.seek(org.apache.hadoop.hbase.KeyValue) (or KeyValueScanner.reseek(org.apache.hadoop.hbase.KeyValue) if forward is true) but only does a seek operation after checking that it is really necessary for the row/column combination specified by the kv parameter.
boolean	shouldUseScanner(Scan scan, SortedSet<byte[]> columns, long oldestUnexpiredTS) Allows to filter out scanners (both StoreFile and memstore) that we don't want to use based on criteria such as Bloom filters and timestamp ranges.

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.hadoop.hbase.regionserver.KeyValueScanner

backwardSeek, close, getSequenceID, next, peek, reseek, seek, seekToLastRow, seekToPreviousRow

Constructor Detail

NonLazyKeyValueScanner

public NonLazyKeyValueScanner()

Method Detail

requestSeek

public boolean requestSeek(KeyValue kv,
                  boolean forward,
                  boolean useBloom)
                    throws IOException

Description copied from interface: KeyValueScanner

Similar to KeyValueScanner.seek(org.apache.hadoop.hbase.KeyValue) (or KeyValueScanner.reseek(org.apache.hadoop.hbase.KeyValue) if forward is true) but only does a seek operation after checking that it is really necessary for the row/column combination specified by the kv parameter. This function was added to avoid unnecessary disk seeks by checking row-column Bloom filters before a seek on multi-column get/scan queries, and to optimize by looking up more recent files first.

Specified by:

requestSeek in interface KeyValueScanner

forward - do a forward-only "reseek" instead of a random-access seek

useBloom - whether to enable multi-column Bloom filter optimization

Throws:

IOException

realSeekDone

public boolean realSeekDone()

Description copied from interface: KeyValueScanner

We optimize our store scanners by checking the most recent store file first, so we sometimes pretend we have done a seek but delay it until the store scanner bubbles up to the top of the key-value heap. This method is then used to ensure the top store file scanner has done a seek operation.

Specified by:

realSeekDone in interface KeyValueScanner

enforceSeek

public void enforceSeek()
                 throws IOException

Description copied from interface: KeyValueScanner

Does the real seek operation in case it was skipped by seekToRowCol(KeyValue, boolean) (TODO: Whats this?). Note that this function should be never called on scanners that always do real seek operations (i.e. most of the scanners). The easiest way to achieve this is to call KeyValueScanner.realSeekDone() first.

Specified by:

enforceSeek in interface KeyValueScanner

Throws:

IOException

doRealSeek

public static boolean doRealSeek(KeyValueScanner scanner,
                 KeyValue kv,
                 boolean forward)
                          throws IOException

Throws:

IOException

shouldUseScanner

public boolean shouldUseScanner(Scan scan,
                       SortedSet<byte[]> columns,
                       long oldestUnexpiredTS)

Description copied from interface: KeyValueScanner

Allows to filter out scanners (both StoreFile and memstore) that we don't want to use based on criteria such as Bloom filters and timestamp ranges.

Specified by:

shouldUseScanner in interface KeyValueScanner

Parameters:

scan - the scan that we are selecting scanners for

columns - the set of columns in the current column family, or null if not specified by the scan

oldestUnexpiredTS - the oldest timestamp we are interested in for this query, based on TTL

Returns:

true if the scanner should be included in the query

isFileScanner

public boolean isFileScanner()

Specified by:

isFileScanner in interface KeyValueScanner

Returns:

true if this is a file scanner. Otherwise a memory scanner is assumed.