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https://issues.apache.org/jira/browse/HBASE-17623?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15862206#comment-15862206
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ChiaPing Tsai commented on HBASE-17623:
---------------------------------------
[~yuzhih...@gmail.com]
{quote}
Have you measured the memory savings through the change ?
Please fix javadoc warning.
{quote}
I was delayed by something. I'll be back. Thanks for your review.
bq. Why is the above check removed ?
h3. before patch
If the compression or encryption is configured, the
HFileBlockDefaultEncodingContext#compressAfterEncoding will return a new bytes
array. Otherwise, the return bytes array is referenced to the input
(uncompressedBlockBytesWithHeader). We need to put the head to both of
onDiskBlockBytesWithHeader and uncompressedBlockBytesWithHeader if they have
different bytes array. Otherwise, we put the head to one of them.
h3. after patch
The check can be removed, because this patch makes the
uncompressedBlockBytesWithHeader and onDiskBlockBytesWithHeader always has the
different bytes array. As a result, we need to put the head to both of them.
> 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: ChiaPing Tsai
> Assignee: ChiaPing Tsai
> Priority: Minor
> Fix For: 2.0.0
>
> Attachments: HBASE-17623.v0.patch
>
>
> There are two improvements.
> # The uncompressedBlockBytesWithHeader and onDiskBlockBytesWithHeader should
> maintain a bytes array which can be reused when building the hfile.
> # The uncompressedBlockBytesWithHeader/onDiskBlockBytesWithHeader is copied
> to an new bytes array only when we need to cache the block.
> {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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