BatchScanner (Apache Accumulo Core 2.0.0 API)

All Superinterfaces:

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

All Known Implementing Classes:

TabletServerBatchDeleter, TabletServerBatchReader
```
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

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	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 java.lang.Iterable
forEach, spliterator

Methods inherited from interface org.apache.accumulo.core.client.ScannerBase
addScanIterator, clearClassLoaderContext, clearColumns, clearSamplerConfiguration, clearScanIterators, fetchColumn, fetchColumn, fetchColumn, fetchColumnFamily, fetchColumnFamily, getAuthorizations, getBatchTimeout, getClassLoaderContext, getSamplerConfiguration, getTimeout, iterator, removeScanIterator, setBatchTimeout, setClassLoaderContext, setExecutionHints, 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