uk.ac.starlink.table.storage.IndexedMappedColumnStore Maven / Gradle / Ivy
package uk.ac.starlink.table.storage;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import uk.ac.starlink.table.Tables;
import uk.ac.starlink.util.DataBufferedOutputStream;
/**
* ColumnStore implementation which uses a mapped buffer and an additional
* auxiliary file to store a fixed number of variable length data items.
*
* @author Mark Taylor
* @since 21 Jun 2006
*/
class IndexedMappedColumnStore implements ColumnStore {
private final Codec codec_;
private final File auxFile_;
private final DataBufferedOutputStream auxOut_;
private ByteBuffer indexBuf_;
private long auxOffset_;
private long nrow_;
private ByteBuffer[] auxBufs_;
/**
* Constructor.
*
* @param codec encoder/decoder for the type of data stored in this
* column
* @param bbuf byte buffer used to store long offset
* values; must be big enough to store 8 bytes for
* each cell
* @param auxFile file used to store the data itself; it is the
* caller's responsibility to clear this up
*/
public IndexedMappedColumnStore( Codec codec, ByteBuffer bbuf,
File auxFile )
throws IOException {
codec_ = codec;
indexBuf_ = bbuf;
auxFile_ = auxFile;
auxOut_ =
new DataBufferedOutputStream( new FileOutputStream( auxFile ) );
}
public void acceptCell( Object value ) throws IOException {
indexBuf_.putLong( auxOffset_ );
auxOffset_ += codec_.encode( value, auxOut_ );
nrow_++;
}
public void endCells() throws IOException {
auxOut_.close();
indexBuf_ = indexBuf_.asReadOnlyBuffer();
auxBufs_ = FileByteStore.toByteBuffers( auxFile_ );
}
public ColumnReader createReader() {
final ByteBuffer ixBuf = indexBuf_.duplicate();
ByteStoreAccess auxAccess =
NioByteStoreAccess
.createAccess( NioByteStoreAccess.copyBuffers( auxBufs_ ) );
return new ByteStoreColumnReader( codec_, auxAccess, nrow_ ) {
public long getAccessOffset( long ix ) {
return ixBuf.getLong( Tables.checkedLongToInt( 8 * ix ) );
}
};
}
}