/// <summary>
/// Merge some number of blocks, how many is decided by mergeFactor, into a single sorted block. This is done by opening <seealso cref="BlockEntryReader"/> on each
/// block that we want to merge and give them to a <seealso cref="MergingBlockEntryReader"/>. The <seealso cref="BlockEntryReader"/>s are pulled from a <seealso cref="BlockReader"/>
/// that iterate over Blocks in file in sequential order.
///
/// <seealso cref="MergingBlockEntryReader"/> pull head from each <seealso cref="BlockEntryReader"/> and hand them out in sorted order, making the multiple entry readers look
/// like a single large and sorted entry reader.
///
/// The large block resulting from the merge is written down to targetChannel by calling
/// <seealso cref="writeBlock(StoreChannel, BlockEntryCursor, long, long, Cancellation, IntConsumer, ByteBuffer)"/>.
/// </summary>
/// <param name="mergeFactor"> How many blocks to merge at the same time. Influence how much memory will be used because each merge block will have it's own
/// <seealso cref="ByteBuffer"/> that they read from. </param>
/// <param name="reader"> The <seealso cref="BlockReader"/> to pull blocks / <seealso cref="BlockEntryReader"/>s from. </param>
/// <param name="targetChannel"> The <seealso cref="StoreChannel"/> to write the merge result to. Result will be appended to current position. </param>
/// <param name="cancellation"> Injected so that this merge can be cancelled, if an external request to do that comes in. </param>
/// <param name="readBuffers"> buffers for all block readers. </param>
/// <param name="writeBuffer"> buffer for writing merged blocks. </param>
/// <returns> The number of blocks that where merged, most often this will be equal to mergeFactor but can be less if there are fewer blocks left in source. </returns>
/// <exception cref="IOException"> If something goes wrong when reading from file. </exception>
//JAVA TO C# CONVERTER WARNING: Method 'throws' clauses are not available in C#:
//ORIGINAL LINE: private int performSingleMerge(int mergeFactor, BlockReader<KEY,VALUE> reader, org.neo4j.io.fs.StoreChannel targetChannel, Cancellation cancellation, ByteBuffer[] readBuffers, ByteBuffer writeBuffer) throws java.io.IOException
private int PerformSingleMerge(int mergeFactor, BlockReader <KEY, VALUE> reader, StoreChannel targetChannel, Cancellation cancellation, ByteBuffer[] readBuffers, ByteBuffer writeBuffer)
{
using (MergingBlockEntryReader <KEY, VALUE> merger = new MergingBlockEntryReader <KEY, VALUE>(_layout))
{
long blockSize = 0;
long entryCount = 0;
int blocksMerged = 0;
for (int i = 0; i < mergeFactor; i++)
{
readBuffers[i].clear();
BlockEntryReader <KEY, VALUE> source = reader.NextBlock(readBuffers[i]);
if (source != null)
{
blockSize += source.BlockSize();
entryCount += source.EntryCount();
blocksMerged++;
merger.AddSource(source);
}
else
{
break;
}
}
writeBuffer.clear();
WriteBlock(targetChannel, merger, blockSize, entryCount, cancellation, _monitor.entriesMerged, writeBuffer);
_monitor.mergedBlocks(blockSize, entryCount, blocksMerged);
return(blocksMerged);
}
}
//JAVA TO C# CONVERTER WARNING: Method 'throws' clauses are not available in C#:
//ORIGINAL LINE: BlockEntryReader<KEY,VALUE> nextBlock(ByteBuffer blockBuffer) throws java.io.IOException
internal virtual BlockEntryReader <KEY, VALUE> NextBlock(ByteBuffer blockBuffer)
{
long position = _channel.position();
if (position >= _channel.size())
{
return(null);
}
StoreChannel blockChannel = _fs.open(_file, OpenMode.READ);
blockChannel.Position(position);
PageCursor pageCursor = new ReadableChannelPageCursor(new ReadAheadChannel <>(blockChannel, blockBuffer));
BlockEntryReader <KEY, VALUE> blockEntryReader = new BlockEntryReader <KEY, VALUE>(pageCursor, _layout);
long blockSize = blockEntryReader.BlockSize();
_channel.position(position + blockSize);
return(blockEntryReader);
}
