org.apache.accumulo.core.client

Interface BatchScanner

All Superinterfaces:

AutoCloseable, Iterable<Map.Entry<Key,Value>>, ScannerBase

All Known Implementing Classes:

MockBatchDeleter, MockBatchScanner

public interface BatchScanner
extends ScannerBase

In exchange for possibly returning scanned entries out of order, BatchScanner implementations may scan an Accumulo table more efficiently by

• Looking up multiple ranges in parallel. Parallelism is constrained by the number of threads available to the BatchScanner, set in its constructor.
• Breaking up large ranges into subranges. Often the number and boundaries of subranges are determined by a table's split points.
• Combining multiple ranges into a single RPC call to a tablet server.

The above techniques lead to better performance than a Scanner in use cases such as

• Retrieving many small ranges
• Scanning a large range that returns many entries
• Running server-side iterators that perform computation, even if few entries are returned from the scan itself

To re-emphasize, only use a BatchScanner when you do not care whether returned data is in sorted order. Use a Scanner instead when sorted order is important.

A BatchScanner instance will use no more threads than provided in the construction of the BatchScanner implementation. Multiple invocations of iterator() will all share the same resources of the instance. A new BatchScanner instance should be created to use allocate additional threads.

Method Summary

Methods

Modifier and Type	Method and Description
void	close() Closes any underlying connections on the scanner.
void	setRanges(Collection<Range> ranges) Allows scanning over multiple ranges efficiently.
void	setTimeout(long timeout, TimeUnit timeUnit) This setting determines how long a scanner will automatically retry when a failure occurs.

Methods inherited from interface org.apache.accumulo.core.client.ScannerBase

addScanIterator, clearClassLoaderContext, clearColumns, clearSamplerConfiguration, clearScanIterators, fetchColumn, fetchColumn, fetchColumnFamily, getAuthorizations, getBatchTimeout, getClassLoaderContext, getSamplerConfiguration, getTimeout, iterator, removeScanIterator, setBatchTimeout, setClassLoaderContext, setSamplerConfiguration, updateScanIteratorOption

Method Detail

setRanges

void setRanges(Collection<Range> ranges)

Allows scanning over multiple ranges efficiently.

Parameters:

ranges - specifies the non-overlapping ranges to query

close

void close()

Description copied from interface: ScannerBase

Closes any underlying connections on the scanner. This may invalidate any iterators derived from the Scanner, causing them to throw exceptions.

Specified by:

close in interface AutoCloseable

Specified by:

close in interface ScannerBase

setTimeout

void setTimeout(long timeout,
              TimeUnit timeUnit)

This setting determines how long a scanner will automatically retry when a failure occurs. By default, a scanner will retry forever.

Setting the timeout to zero (with any time unit) or Long.MAX_VALUE (with TimeUnit.MILLISECONDS) means no timeout.

The batch scanner will accomplish as much work as possible before throwing an exception. BatchScanner iterators will throw a TimedOutException when all needed servers timeout.

Specified by:

setTimeout in interface ScannerBase

Parameters:

timeout - the length of the timeout

timeUnit - the units of the timeout