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https://issues.apache.org/jira/browse/HBASE-5074?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Phabricator updated HBASE-5074:
-------------------------------
Attachment: D1521.1.patch
dhruba requested code review of "[jira] [HBASE-5074] Support checksums in HBase
block cache".
Reviewers: mbautin
HFile is enhanced to store a checksum for each block. HDFS checksum
verification is avoided while reading data into the block cache. On a checksum
verification failure, we retry the file system read request with hdfs checksums
switched on (thanks Todd).
I have a benchmark that shows that it reduces iops on the disk by about 40%.
In this experiment, the entire memory on the regionserver is allocated to the
regionserver's jvm and the OS buffer cache size is negligible. I also measured
negligible (<5%) additional cpu usage while using hbase-level checksums.
The salient points of this patch:
1. Each hfile's trailer used to have a 4 byte version number. I enhanced this
so that these 4 bytes can be interpreted as a (major version number, minor
version). Pre-existing hfiles have a minor version of 0. The new hfile format
has a minor version of 1 (thanks Mikhail). The hfile major version remains
unchanged at 2. The reason I did not introduce a new major version number is
because the code changes needed to store/read checksums do not differ much from
existing V2 writers/readers.
2. Introduced a HFileSystem object which is a encapsulates the FileSystem
objects needed to access data from hfiles and hlogs. HDFS FileSystem objects
already had the ability to switch off checksum verifications for reads.
3. The majority of the code changes are located in hbase.io.hfie package. The
retry of a read on an initial checksum failure occurs inside the hbase.io.hfile
package itself. The code changes to hbase.regionserver package are minor.
4. The format of a hfileblock is the header followed by the data followed by
the checksum(s). Each 16 K (configurable) size of data has a 4 byte checksum.
The hfileblock header has two additional fields: a 4 byte value to store the
bytesPerChecksum and a 4 byte value to store the size of the user data
(excluding the checksum data). This is well explained in the associated
javadocs.
5. I added a test to test backward compatibility. I will be writing more unit
tests that triggers checksum verification failures aggressively. I have left a
few redundant log messages in the code (just for easier debugging) and will
remove them in later stage of this patch. I will also be adding metrics on
number of checksum verification failures/success in a later version of this
diff.
6. By default, hbase-level checksums are switched on and hdfs level checksums
are switched off for hfile-reads. No changes to Hlog code path here.
TEST PLAN
The default setting is to switch on hbase checksums for hfile-reads, thus all
existing tests actually validate the new code pieces. I will be writing more
unit tests for triggering checksum verification failures.
REVISION DETAIL
https://reviews.facebook.net/D1521
AFFECTED FILES
src/test/java/org/apache/hadoop/hbase/HBaseTestingUtility.java
src/test/java/org/apache/hadoop/hbase/HBaseTestCase.java
src/test/java/org/apache/hadoop/hbase/regionserver/TestSplitTransaction.java
src/test/java/org/apache/hadoop/hbase/regionserver/wal/TestWALReplay.java
src/test/java/org/apache/hadoop/hbase/regionserver/TestScanWithBloomError.java
src/test/java/org/apache/hadoop/hbase/regionserver/TestCompoundBloomFilter.java
src/test/java/org/apache/hadoop/hbase/regionserver/TestStore.java
src/test/java/org/apache/hadoop/hbase/regionserver/TestStoreFile.java
src/test/java/org/apache/hadoop/hbase/io/hfile/TestHFileBlock.java
src/test/java/org/apache/hadoop/hbase/io/hfile/TestCacheOnWrite.java
src/test/java/org/apache/hadoop/hbase/io/hfile/TestHFileReaderV1.java
src/test/java/org/apache/hadoop/hbase/io/hfile/CacheTestUtils.java
src/test/java/org/apache/hadoop/hbase/io/hfile/TestHFileBlockIndex.java
src/test/java/org/apache/hadoop/hbase/io/hfile/TestHFileDataBlockEncoder.java
src/test/java/org/apache/hadoop/hbase/io/hfile/TestHFileBlockCompatibility.java
src/test/java/org/apache/hadoop/hbase/io/TestHalfStoreFileReader.java
src/test/java/org/apache/hadoop/hbase/util/TestMergeTable.java
src/main/java/org/apache/hadoop/hbase/HConstants.java
src/main/java/org/apache/hadoop/hbase/util/HFileSystem.java
src/main/java/org/apache/hadoop/hbase/util/ChecksumByteArrayOutputStream.java
src/main/java/org/apache/hadoop/hbase/util/CompoundBloomFilter.java
src/main/java/org/apache/hadoop/hbase/util/ChecksumFactory.java
src/main/java/org/apache/hadoop/hbase/regionserver/handler/OpenRegionHandler.java
src/main/java/org/apache/hadoop/hbase/regionserver/HRegion.java
src/main/java/org/apache/hadoop/hbase/regionserver/HRegionServer.java
src/main/java/org/apache/hadoop/hbase/io/hfile/HFileBlock.java
src/main/java/org/apache/hadoop/hbase/io/hfile/HFilePrettyPrinter.java
src/main/java/org/apache/hadoop/hbase/io/hfile/HFileDataBlockEncoderImpl.java
src/main/java/org/apache/hadoop/hbase/io/hfile/HFileReaderV2.java
src/main/java/org/apache/hadoop/hbase/io/hfile/HFile.java
src/main/java/org/apache/hadoop/hbase/io/hfile/HFileWriterV2.java
src/main/java/org/apache/hadoop/hbase/io/hfile/HFileDataBlockEncoder.java
src/main/java/org/apache/hadoop/hbase/io/hfile/AbstractHFileReader.java
src/main/java/org/apache/hadoop/hbase/io/hfile/NoOpDataBlockEncoder.java
src/main/java/org/apache/hadoop/hbase/io/hfile/FixedFileTrailer.java
src/main/java/org/apache/hadoop/hbase/io/hfile/HFileWriterV1.java
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> support checksums in HBase block cache
> --------------------------------------
>
> Key: HBASE-5074
> URL: https://issues.apache.org/jira/browse/HBASE-5074
> Project: HBase
> Issue Type: Improvement
> Components: regionserver
> Reporter: dhruba borthakur
> Assignee: dhruba borthakur
> Attachments: D1521.1.patch, D1521.1.patch
>
>
> The current implementation of HDFS stores the data in one block file and the
> metadata(checksum) in another block file. This means that every read into the
> HBase block cache actually consumes two disk iops, one to the datafile and
> one to the checksum file. This is a major problem for scaling HBase, because
> HBase is usually bottlenecked on the number of random disk iops that the
> storage-hardware offers.
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