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https://issues.apache.org/jira/browse/HBASE-17623?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15896834#comment-15896834
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Anoop Sam John commented on HBASE-17623:
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Understood the patch. So we avoid the need to copy many times.
'baosInMemory' is still there and we keep accumulating cells to that. Once the
block to be written to HFile, it will go there with no extra copy , if there
are no encryption/compression AND no need for cache on write. When encryption
of compression is present, we use the same baosInMemory stream to create new
encrypted/compressed stream. When cache on write, we will end up in copying
both onDisk and uncompressed streams.
{code}
if (compressAndEncryptDat == null) {
1031 compressAndEncryptDat = new Bytes(baosInMemory.getBuffer(), 0,
baosInMemory.size());
1032 }
{code}
This case is not really possible right?
bq.private ByteArrayOutputStream onDiskBlockBytesWithHeader;
Why this specific change is needed now? Why we can not continue to have the
type as byte[]? So may be then we will have to keep the size also? Offset will
be any way 0. Just asking
> Reuse the bytes array when building the hfile block
> ---------------------------------------------------
>
> Key: HBASE-17623
> URL: https://issues.apache.org/jira/browse/HBASE-17623
> Project: HBase
> Issue Type: Improvement
> Reporter: CHIA-PING TSAI
> Assignee: CHIA-PING TSAI
> Priority: Minor
> Fix For: 2.0.0, 1.4.0
>
> Attachments: after(snappy_hfilesize=5.04GB).png,
> after(snappy_hfilesize=755MB).png, before(snappy_hfilesize=5.04GB).png,
> before(snappy_hfilesize=755MB).png, HBASE-17623.branch-1.v0.patch,
> HBASE-17623.branch-1.v1.patch, HBASE-17623.branch-1.v2.patch,
> HBASE-17623.branch-1.v2.patch, HBASE-17623.v0.patch, HBASE-17623.v1.patch,
> HBASE-17623.v1.patch, HBASE-17623.v2.patch, memory allocation measurement.xlsx
>
>
> There are two improvements.
> # The onDiskBlockBytesWithHeader should maintain a bytes array which can be
> reused when building the hfile.
> # The onDiskBlockBytesWithHeader is copied to an new bytes array only when we
> need to cache the block.
> # If no block need to be cached, the uncompressedBlockBytesWithHeader will
> never be created.
> {code:title=HFileBlock.java|borderStyle=solid}
> private void finishBlock() throws IOException {
> if (blockType == BlockType.DATA) {
> this.dataBlockEncoder.endBlockEncoding(dataBlockEncodingCtx,
> userDataStream,
> baosInMemory.getBuffer(), blockType);
> blockType = dataBlockEncodingCtx.getBlockType();
> }
> userDataStream.flush();
> // This does an array copy, so it is safe to cache this byte array when
> cache-on-write.
> // Header is still the empty, 'dummy' header that is yet to be filled
> out.
> uncompressedBlockBytesWithHeader = baosInMemory.toByteArray();
> prevOffset = prevOffsetByType[blockType.getId()];
> // We need to set state before we can package the block up for
> cache-on-write. In a way, the
> // block is ready, but not yet encoded or compressed.
> state = State.BLOCK_READY;
> if (blockType == BlockType.DATA || blockType == BlockType.ENCODED_DATA)
> {
> onDiskBlockBytesWithHeader = dataBlockEncodingCtx.
> compressAndEncrypt(uncompressedBlockBytesWithHeader);
> } else {
> onDiskBlockBytesWithHeader = defaultBlockEncodingCtx.
> compressAndEncrypt(uncompressedBlockBytesWithHeader);
> }
> // Calculate how many bytes we need for checksum on the tail of the
> block.
> int numBytes = (int) ChecksumUtil.numBytes(
> onDiskBlockBytesWithHeader.length,
> fileContext.getBytesPerChecksum());
> // Put the header for the on disk bytes; header currently is
> unfilled-out
> putHeader(onDiskBlockBytesWithHeader, 0,
> onDiskBlockBytesWithHeader.length + numBytes,
> uncompressedBlockBytesWithHeader.length,
> onDiskBlockBytesWithHeader.length);
> // Set the header for the uncompressed bytes (for cache-on-write) --
> IFF different from
> // onDiskBlockBytesWithHeader array.
> if (onDiskBlockBytesWithHeader != uncompressedBlockBytesWithHeader) {
> putHeader(uncompressedBlockBytesWithHeader, 0,
> onDiskBlockBytesWithHeader.length + numBytes,
> uncompressedBlockBytesWithHeader.length,
> onDiskBlockBytesWithHeader.length);
> }
> if (onDiskChecksum.length != numBytes) {
> onDiskChecksum = new byte[numBytes];
> }
> ChecksumUtil.generateChecksums(
> onDiskBlockBytesWithHeader, 0, onDiskBlockBytesWithHeader.length,
> onDiskChecksum, 0, fileContext.getChecksumType(),
> fileContext.getBytesPerChecksum());
> }{code}
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