Package uk.ac.starlink.table.storage
Class AdaptiveByteStore
- java.lang.Object
-
- uk.ac.starlink.table.storage.AdaptiveByteStore
-
- All Implemented Interfaces:
ByteStore
public class AdaptiveByteStore extends java.lang.Object implements ByteStore
ByteStore which adopts a hybrid approach between use of memory and use of disk. Bytes are written into an array in memory up to a given size limit; if the amount written exceeds this limit, it's all put in a temporary file instead.This class is intended to be a general purpose StoragePolicy implementation that does something sensible most of the time. The details of the implementation may be changed following experience.
The current implementation uses
ByteBuffer.allocateDirect(int)
for byte arrays in memory apart from rather small ones. On most OSes this corresponds to usingmalloc()
, thus avoiding heavy use of JVM heap memory. Note very large arrays are still stored on disk, not directly allocated.- Since:
- 5 Nov 2009
- Author:
- Mark Taylor
-
-
Constructor Summary
Constructors Constructor Description AdaptiveByteStore()
Constructs a new store with a default memory limit.AdaptiveByteStore(int memLimit)
Constructs a new store with a given maximum memory limit.
-
Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
close()
Tidies up.void
copy(java.io.OutputStream out)
Takes all the data written so far into this store's sink stream and copies it to a destination stream.long
getLength()
Returns the number of bytes currently stored in this object.java.io.OutputStream
getOutputStream()
Returns an output stream which can be used to write to the store.java.nio.ByteBuffer[]
toByteBuffers()
Returns an array of byte buffers containing the bytes written to this store.
-
-
-
Constructor Detail
-
AdaptiveByteStore
public AdaptiveByteStore(int memLimit) throws java.io.IOException
Constructs a new store with a given maximum memory limit.- Parameters:
memLimit
- maximum size of in-memory buffer- Throws:
java.io.IOException
-
AdaptiveByteStore
public AdaptiveByteStore() throws java.io.IOException
Constructs a new store with a default memory limit.- Throws:
java.io.IOException
-
-
Method Detail
-
getOutputStream
public java.io.OutputStream getOutputStream()
Description copied from interface:ByteStore
Returns an output stream which can be used to write to the store. May be called multiple times; always returns the same object. Note that this is not in general buffered - it is the responsibility of the user to take steps like wrapping it in aBufferedOutputStream
for efficiency if required.- Specified by:
getOutputStream
in interfaceByteStore
- Returns:
- data sink stream
-
getLength
public long getLength()
Description copied from interface:ByteStore
Returns the number of bytes currently stored in this object.
-
copy
public void copy(java.io.OutputStream out) throws java.io.IOException
Description copied from interface:ByteStore
Takes all the data written so far into this store's sink stream and copies it to a destination stream. The output stream is not closed.
-
toByteBuffers
public java.nio.ByteBuffer[] toByteBuffers() throws java.io.IOException
Description copied from interface:ByteStore
Returns an array of byte buffers containing the bytes written to this store. The stored bytes are all of the bytes from the first buffer in the returned array, followed by all in the second, etc. In many cases the returned array will, and probably should, contain a single buffer, but if the written byte count exceedsInteger.MAX_VALUE
, more than one will be required. The limit of each buffer indicates the number of bytes it contains.Usual usage will be to write all data, then call this method once; this model may affect implementation decisions about efficiency.
- Specified by:
toByteBuffers
in interfaceByteStore
- Returns:
- byte buffer containing bytes written
- Throws:
java.io.IOException
- if there is an I/O error
-
-