* Add FileUtils.createTempDir() and enforce its usage.
The purpose of this is to improve error messages. Previously, the error
message on a nonexistent or unwritable temp directory would be
"Failed to create directory within 10,000 attempts".
* Further updates.
* Another update.
* Remove commons-io from benchmark.
* Fix tests.
* add TsvInputFormat
* refactor code
* fix grammar
* use enum replace string literal
* code refactor
* code refactor
* mark abstract for base class meant not to be instantiated
* remove constructor for test
* add parquet support to native batch
* cleanup
* implement toJson for sampler support
* better binaryAsString test
* docs
* i hate spellcheck
* refactor toMap conversion so can be shared through flattenerMaker, default impls should be good enough for orc+avro, fixup for merge with latest
* add comment, fix some stuff
* adjustments
* fix accident
* tweaks
* Refactor parallel indexing perfect rollup partitioning
Refactoring to make it easier to later add range partitioning for
perfect rollup parallel indexing. This is accomplished by adding several
new base classes (e.g., PerfectRollupWorkerTask) and new classes for
encapsulating logic that needs to be changed for different partitioning
strategies (e.g., IndexTaskInputRowIteratorBuilder).
The code is functionally equivalent to before except for the following
small behavior changes:
1) PartialSegmentMergeTask: Previously, this task had a priority of
DEFAULT_TASK_PRIORITY. It now has a priority of
DEFAULT_BATCH_INDEX_TASK_PRIORITY (via the new PerfectRollupWorkerTask
base class), since it is a batch index task.
2) ParallelIndexPhaseRunner: A decorator was added to
subTaskSpecIterator to ensure the subtasks are generated with unique
ids. Previously, only tests (i.e., MultiPhaseParallelIndexingTest)
would have this decorator, but this behavior is desired for non-test
code as well.
* Fix forbidden apis and pmd warnings
* Fix analyze dependencies warnings
* Fix IndexTask json and add IT diags
* Fix parallel index supervisor<->worker serde
* Fix TeamCity inspection errors/warnings
* Fix TeamCity inspection errors/warnings again
* Integrate changes with those from #8823
* Address review comments
* Address more review comments
* Fix forbidden apis
* Address more review comments
* HDFS input source
Add support for using HDFS as an input source. In this version, commas
or globs are not supported in HDFS paths.
* Fix forbidden api
* Address review comments
* Tidy up lifecycle, query, and ingestion logging.
The goal of this patch is to improve the clarity and usefulness of
Druid's logging for cluster operators. For more information, see
https://twitter.com/cowtowncoder/status/1195469299814555648.
Concretely, this patch does the following:
- Changes a lot of INFO logs to DEBUG, and DEBUG to TRACE, with the
goal of reducing redundancy and improving clarity by avoiding
showing rarely-useful log messages. This includes most "starting"
and "stopping" messages, and most messages related to individual
columns.
- Adds new log4j2 templates that show operators how to enabled DEBUG
logging for certain important packages.
- Eliminate stack traces for query errors, unless log level is DEBUG
or more. This is useful because query errors often indicate user
error rather than system error, but dumping stack trace often gave
operators the impression that there was a system failure.
- Adds task id to Appenderator, AppenderatorDriver thread names. In
the default log4j2 configuration, this will put them in log lines
as well. It's very useful if a user is using the Indexer, where
multiple tasks run in the same JVM.
- More consistent terminology when it comes to "sequences" (sets of
segments that are handed-off together by Kafka ingestion) and
"offsets" (cursors in partitions). These terms had been confused in
some log messages due to the fact that Kinesis calls offsets
"sequence numbers".
- Replaces some ugly toString calls with either the JSONification or
something more operator-accessible (like a URL or segment identifier,
instead of JSON object representing the same).
* Adjustments.
* Adjust integration test.
* transformSpec + array expressions
changes:
* added array expression support to transformSpec
* removed ParseSpec.verify since its only use afaict was preventing transform expr that did not replace their input from functioning
* hijacked index task test to test changes
* remove docs about being unsupported
* re-arrange test assert
* unused imports
* imports
* fix tests
* preserve types
* suppress warning, fixes, add test
* formatting
* cleanup
* better list to array type conversion and tests
* fix oops
There is a class of bugs due to the fact that BaseObjectColumnValueSelector
has both "getObject" and "isNull" methods, but in most selector implementations
and most call sites, it is clear that the intent of "isNull" is only to apply
to the primitive getters, not the object getter. This makes sense, because the
purpose of isNull is to enable detection of nulls in otherwise-primitive columns.
Imagine a string column with a numeric selector built on top of it. You would
want it to return isNull = true, so numeric aggregators don't treat it as
all zeroes.
Sometimes this design leads people to accidentally guard non-primitive get
methods with "selector.isNull" checks, which is improper.
This patch has three goals:
1) Fix null-handling bugs that already exist in this class.
2) Make interface and doc changes that reduce the probability of future bugs.
3) Fix other, unrelated bugs I noticed in the stringFirst and stringLast
aggregators while fixing null-handling bugs. I thought about splitting this
into its own patch, but it ended up being tough to split from the
null-handling fixes.
For (1) the fixes are,
- Fix StringFirst and StringLastAggregatorFactory to stop guarding getObject
calls on isNull, by no longer extending NullableAggregatorFactory. Now uses
-1 as a sigil value for null, to differentiate nulls and empty strings.
- Fix ExpressionFilter to stop guarding getObject calls on isNull. Also, use
eval.asBoolean() to avoid calling getLong on the selector after already
calling getObject.
- Fix ObjectBloomFilterAggregator to stop guarding DimensionSelector calls
on isNull. Also, refactored slightly to avoid the overhead of calling
getObject followed by another getter (see BloomFilterAggregatorFactory for
part of this).
For (2) the main changes are,
- Remove the "isNull" method from BaseObjectColumnValueSelector.
- Clarify "isNull" doc on BaseNullableColumnValueSelector.
- Rename NullableAggregatorFactory -> NullbleNumericAggregatorFactory to emphasize
that it only works on aggregators that take numbers as input.
- Similar naming changes to the Aggregator, BufferAggregator, and AggregateCombiner.
- Similar naming changes to helper methods for groupBy, ValueMatchers, etc.
For (3) the other fixes for StringFirst and StringLastAggregatorFactory are,
- Fixed buffer overrun in the buffer aggregators when some characters in the string
code into more than one byte (the old code used "substring" to apply a byte limit,
which is bad). I did this by introducing a new StringUtils.toUtf8WithLimit method.
- Fixed weird IncrementalIndex logic that led to reading nulls for the timestamp.
- Adjusted weird StringFirst/Last logic that worked around the weird IncrementalIndex
behavior.
- Refactored to share code between the four aggregators.
- Improved test coverage.
- Made the base stringFirst, stringLast aggregators adaptive, and streamlined the
xFold versions into aliases. The adaptiveness is similar to how other aggregators
like hyperUnique work.
* sketch of broker parallel merges done in small batches on fork join pool
* fix non-terminating sequences, auto compute parallelism
* adjust benches
* adjust benchmarks
* now hella more faster, fixed dumb
* fix
* remove comments
* log.info for debug
* javadoc
* safer block for sequence to yielder conversion
* refactor LifecycleForkJoinPool into LifecycleForkJoinPoolProvider which wraps a ForkJoinPool
* smooth yield rate adjustment, more logs to help tune
* cleanup, less logs
* error handling, bug fixes, on by default, more parallel, more tests
* remove unused var
* comments
* timeboundary mergeFn
* simplify, more javadoc
* formatting
* pushdown config
* use nanos consistently, move logs back to debug level, bit more javadoc
* static terminal result batch
* javadoc for nullability of createMergeFn
* cleanup
* oops
* fix race, add docs
* spelling, remove todo, add unhandled exception log
* cleanup, revert unintended change
* another unintended change
* review stuff
* add ParallelMergeCombiningSequenceBenchmark, fixes
* hyper-threading is the enemy
* fix initial start delay, lol
* parallelism computer now balances partition sizes to partition counts using sqrt of sequence count instead of sequence count by 2
* fix those important style issues with the benchmarks code
* lazy sequence creation for benchmarks
* more benchmark comments
* stable sequence generation time
* update defaults to use 100ms target time, 4096 batch size, 16384 initial yield, also update user docs
* add jmh thread based benchmarks, cleanup some stuff
* oops
* style
* add spread to jmh thread benchmark start range, more comments to benchmarks parameters and purpose
* retool benchmark to allow modeling more typical heterogenous heavy workloads
* spelling
* fix
* refactor benchmarks
* formatting
* docs
* add maxThreadStartDelay parameter to threaded benchmark
* why does catch need to be on its own line but else doesnt
* IndexerSQLMetadataStorageCoordinator.getTimelineForIntervalsWithHandle() don't fetch abutting intervals; simplify getUsedSegmentsForIntervals()
* Add VersionedIntervalTimeline.findNonOvershadowedObjectsInInterval() method; Propagate the decision about whether only visible segmetns or visible and overshadowed segments should be returned from IndexerMetadataStorageCoordinator's methods to the user logic; Rename SegmentListUsedAction to RetrieveUsedSegmentsAction, SegmetnListUnusedAction to RetrieveUnusedSegmentsAction, and UsedSegmentLister to UsedSegmentsRetriever
* Fix tests
* More fixes
* Add javadoc notes about returning Collection instead of Set. Add JacksonUtils.readValue() to reduce boilerplate code
* Fix KinesisIndexTaskTest, factor out common parts from KinesisIndexTaskTest and KafkaIndexTaskTest into SeekableStreamIndexTaskTestBase
* More test fixes
* More test fixes
* Add a comment to VersionedIntervalTimelineTestBase
* Fix tests
* Set DataSegment.size(0) in more tests
* Specify DataSegment.size(0) in more places in tests
* Fix more tests
* Fix DruidSchemaTest
* Set DataSegment's size in more tests and benchmarks
* Fix HdfsDataSegmentPusherTest
* Doc changes addressing comments
* Extended doc for visibility
* Typo
* Typo 2
* Address comment
* remove select query
* thanks teamcity
* oops
* oops
* add back a SelectQuery class that throws RuntimeExceptions linking to docs
* adjust text
* update docs per review
* deprecated
When using single-dimension partitioning, use targetRowsPerSegment (if
specified) to size segments. Previously, single-dimension partitioning
would always size segments as close to the max size as possible.
Also, change single-dimension partitioning to allow partitions that have
a size equal to the target or max size. Previously, it would create
partitions up to 1 less than those limits.
Also, fix some IntelliJ inspection warnings in HadoopDruidIndexerConfig.
* Stateful auto compaction
* javaodc
* add removed test back
* fix test
* adding indexSpec to compactionState
* fix build
* add lastCompactionState
* address comments
* extract CompactionState
* fix doc
* fix build and test
* Add a task context to store compaction state; add javadoc
* fix it test
* IOConfig for compaction task
* add javadoc, doc, unit test
* fix webconsole test
* add spelling
* address comments
* fix build and test
* address comments
* Make more package EverythingIsNonnullByDefault by default
* Fixed additional voilations after pulling in master
* Change iterator to list.addAll
* Fix annotations
* Adjust defaults for hashed partitioning
If neither the partition size nor the number of shards are specified,
default to partitions of 5,000,000 rows (similar to the behavior of
dynamic partitions). Previously, both could be null and cause incorrect
behavior.
Specifying both a partition size and a number of shards now results in
an error instead of ignoring the partition size in favor of using the
number of shards. This is a behavior change that makes it more apparent
to the user that only one of the two properties will be honored
(previously, a message was just logged when the specified partition size
was ignored).
* Fix test
* Handle -1 as null
* Add -1 as null tests for single dim partitioning
* Simplify logic to handle -1 as null
* Address review comments
* Rename partition spec fields
Rename partition spec fields to be consistent across the various types
(hashed, single_dim, dynamic). Specifically, use targetNumRowsPerSegment
and maxRowsPerSegment in favor of targetPartitionSize and
maxSegmentSize. Consistent and clearer names are easier for users to
understand and use.
Also fix various IntelliJ inspection warnings and doc spelling mistakes.
* Fix test
* Improve docs
* Add targetRowsPerSegment to HashedPartitionsSpec
* Fix dependency analyze warnings
Update the maven dependency plugin to the latest version and fix all
warnings for unused declared and used undeclared dependencies in the
compile scope. Added new travis job to add the check to CI. Also fixed
some source code files to use the correct packages for their imports and
updated druid-forbidden-apis to prevent regressions.
* Address review comments
* Adjust scope for org.glassfish.jaxb:jaxb-runtime
* Fix dependencies for hdfs-storage
* Consolidate netty4 versions
* Exit JVM on curator unhandled errors
If an unhandled error occurs when curator is talking to ZooKeeper, exit
the JVM in addition to stopping the lifecycle to prevent the process
from being left in a zombie state. With this change,
BoundedExponentialBackoffRetryWithQuit is no longer needed as when
curator exceeds the configured retries, it triggers its unhandled error
listeners. A new "connectionTimeoutMs" CuratorConfig setting is added
mostly to facilitate testing curator unhandled errors, but it may be
useful for users as well.
* Address review comments
* string column handling for long min/max/sum aggregators
* add apache license to new files
* use 'L' as suffix for long literal instead of 'l'
* return null in ParallelCombiner.SettableColumnSelectorFactory.getColumnCapabilities(String) as is required by contract of ColumnSelectorFactory interface
* fix more tests
* LoggingEmitter: print event as json
* use DefaultRequestLogEventBuilderFactory in emitting request logger by default
* print context in query metric as json
* removed unused jsonMapper from DefaultQueryMetrics
* add comment
* remove change to DefaultRequestLogEventBuilderFactory.java
* Speed up ExpressionSelectors.makeExprEvalSelector
Addresses performance bottlenecks observed when running a search query
with an expression filter and granularity set to none by caching and
changing streams to for-loops. After changes, the query was observed to
run 2-3x faster.
Also fixes various IntelliJ inspection warnings.
* Fix static analysis errors
JVMMonitor requires access to jdk.internal.perf.Perf to enable GC
counters, which requires additional JVM arguments with JDK11.
This change adds a fallback in case GC counters cannot be initialized,
and logs a warning message explaining how GC counters can be enabled.
* Fallback to parsing classpath for hadoop task in Java 9+
In Java 9 and above we cannot assume that the system classloader is an
instance of URLClassLoader. This change adds a fallback method to parse
the system classpath in that case, and adds a unit test to validate it matches
what JDK8 would do.
Note: This has not been tested in an actual hadoop setup, so this is mostly
to help us pass unit tests.
* Remove granularity test of dubious value
One of our granularity tests relies on system classloader being a URLClassLoaders to
catch a bug related to class initialization and static initializers using a subclass (see
#2979)
This test was added to catch a potential regression, but it assumes we would add back
the same type of static initializers to this specific class, so it seems to be of dubious value
as a unit test and mostly serves to illustrate the bug.
relates to #5589
* check ctyle for constant field name
* check ctyle for constant field name
* check ctyle for constant field name
* check ctyle for constant field name
* check ctyle for constant field name
* check ctyle for constant field name
* check ctyle for constant field name
* check ctyle for constant field name
* check ctyle for constant field name
* merging with upstream
* review-1
* unknow changes
* unknow changes
* review-2
* merging with master
* review-2 1 changes
* review changes-2 2
* bug fix
* Add group_id to overlord tasks API and sys.tasks table
* adjust test
* modify docs
* Make groupId nullable
* fix integration test
* fix toString
* Remove groupId from TaskInfo
* Modify docs and tests
* modify TaskMonitorTest
* Enable code coverage
Code coverage was disabled via
https://github.com/apache/incubator-druid/pull/3122 due to an issue with
cobertura in Travis CI. Switch code coverage tool from cobertura to
jacoco to avoid issue and re-enable coveralls for Travis CI.
* Exclude non-production code
* Exclude benchmark generated code
* Exclude DruidTestRunnerFactory
* Add TaskResourceCleaner; fix a couple of concurrency bugs in batch tasks
* kill runner when it's ready
* add comment
* kill run thread
* fix test
* Take closeable out of Appenderator
* add javadoc
* fix test
* fix test
* update javadoc
* add javadoc about killed task
* address comment
* Add support for parallel native indexing with shuffle for perfect rollup.
* Add comment about volatiles
* fix test
* fix test
* handling missing exceptions
* more clear javadoc for stopGracefully
* unused import
* update javadoc
* Add missing statement in javadoc
* address comments; fix doc
* add javadoc for isGuaranteedRollup
* Rename confusing variable name and fix typos
* fix typos; move fetch() to a better home; fix the expiration time
* add support https
* make double sum/min/max agg work on string columns
* style and compilation fixes
* fix tests
* address review comments
* add comment on SimpleDoubleAggregatorFactory
* make checkstyle happy
After enabling parallel builds for "mvn install", the sigar dependency
would sometimes resolve to the incorrect artifact repo for some of the
maven modules. This issue seems to be fixed by moving the definition of
the sigar dependency's artifact repo to the root POM.
Also, depending on network speeds, "mvn -q install" may take longer than
the default 10 minute timeout to print any output. Use travis_wait to
extend the timeout to 15 minutes.
* Use partitionsSpec for all task types
* fix doc
* fix typos and revert to use isPushRequired
* address comments
* move partitionsSpec to core
* remove hadoopPartitionsSpec
* firehose doc adjustments
* fix typo
* additional information on parser types in ingestion docs
* clarify ingest segment firehose docs, add sql firehose examples to sql extension pages
* fixit
* make sql firehose more forgiving my always constructing a MapInputRowParser from the parseSpec of whatever actual InputRowParser impl is provided, remove doc references to map based parsers
* transforms
* fix tests
* Fix dependency analyze warnings
Update the maven dependency plugin to the latest version and fix all
warnings for unused declared and used undeclared dependencies in the
compile scope. Added new travis job to add the check to CI. Also fixed
some source code files to use the correct packages for their imports.
* Fix licenses and dependencies
* Fix licenses and dependencies again
* Fix integration test dependency
* Address review comments
* Fix unit test dependencies
* Fix integration test dependency
* Fix integration test dependency again
* Fix integration test dependency third time
* Fix integration test dependency fourth time
* Fix compile error
* Fix assert package
* add CachingClusteredClient benchmark, refactor some stuff
* revert WeightedServerSelectorStrategy to ConnectionCountServerSelectorStrategy and remove getWeight since felt artificial, default mergeResults in toolchest implementation for topn, search, select
* adjust javadoc
* adjustments
* oops
* use it
* use BinaryOperator, remove CombiningFunction, use Comparator instead of Ordering, other review adjustments
* rename createComparator to createResultComparator, fix typo, firstNonNull nullable parameters
* doc updates and changes to use the CollectionUtils.mapValues utility method
* Add Structural Search patterns to intelliJ
* refactoring from PR comments
* put -> putIfAbsent
* do single key lookup
* Benchmarks: New SqlBenchmark, add caching & vectorization to some others.
- Introduce a new SqlBenchmark geared towards benchmarking a wide
variety of SQL queries. Rename the old SqlBenchmark to
SqlVsNativeBenchmark.
- Add (optional) caching to SegmentGenerator to enable easier
benchmarking of larger segments.
- Add vectorization to FilteredAggregatorBenchmark and GroupByBenchmark.
* Query vectorization.
This patch includes vectorized timeseries and groupBy engines, as well
as some analogs of your favorite Druid classes:
- VectorCursor is like Cursor. (It comes from StorageAdapter.makeVectorCursor.)
- VectorColumnSelectorFactory is like ColumnSelectorFactory, and it has
methods to create analogs of the column selectors you know and love.
- VectorOffset and ReadableVectorOffset are like Offset and ReadableOffset.
- VectorAggregator is like BufferAggregator.
- VectorValueMatcher is like ValueMatcher.
There are some noticeable differences between vectorized and regular
execution:
- Unlike regular cursors, vector cursors do not understand time
granularity. They expect query engines to handle this on their own,
which a new VectorCursorGranularizer class helps with. This is to
avoid too much batch-splitting and to respect the fact that vector
selectors are somewhat more heavyweight than regular selectors.
- Unlike FilteredOffset, FilteredVectorOffset does not leverage indexes
for filters that might partially support them (like an OR of one
filter that supports indexing and another that doesn't). I'm not sure
that this behavior is desirable anyway (it is potentially too eager)
but, at any rate, it'd be better to harmonize it between the two
classes. Potentially they should both do some different thing that
is smarter than what either of them is doing right now.
- When vector cursors are created by QueryableIndexCursorSequenceBuilder,
they use a morphing binary-then-linear search to find their start and
end rows, rather than linear search.
Limitations in this patch are:
- Only timeseries and groupBy have vectorized engines.
- GroupBy doesn't handle multi-value dimensions yet.
- Vector cursors cannot handle virtual columns or descending order.
- Only some filters have vectorized matchers: "selector", "bound", "in",
"like", "regex", "search", "and", "or", and "not".
- Only some aggregators have vectorized implementations: "count",
"doubleSum", "floatSum", "longSum", "hyperUnique", and "filtered".
- Dimension specs other than "default" don't work yet (no extraction
functions or filtered dimension specs).
Currently, the testing strategy includes adding vectorization-enabled
tests to TimeseriesQueryRunnerTest, GroupByQueryRunnerTest,
GroupByTimeseriesQueryRunnerTest, CalciteQueryTest, and all of the
filtering tests that extend BaseFilterTest. In all of those classes,
there are some test cases that don't support vectorization. They are
marked by special function calls like "cannotVectorize" or "skipVectorize"
that tell the test harness to either expect an exception or to skip the
test case.
Testing should be expanded in the future -- a project in and of itself.
Related to #3011.
* WIP
* Adjustments for unused things.
* Adjust javadocs.
* DimensionDictionarySelector adjustments.
* Add "clone" to BatchIteratorAdapter.
* ValueMatcher javadocs.
* Fix benchmark.
* Fixups post-merge.
* Expect exception on testGroupByWithStringVirtualColumn for IncrementalIndex.
* BloomDimFilterSqlTest: Tag two non-vectorizable tests.
* Minor adjustments.
* Update surefire, bump up Xmx in Travis.
* Some more adjustments.
* Javadoc adjustments
* AggregatorAdapters adjustments.
* Additional comments.
* Remove switching search.
* Only missiles.
Make static imports forbidden in tests and remove all occurrences to be
consistent with the non-test code.
Also, various changes to files affected by above:
- Reformat to adhere to druid style guide
- Fix various IntelliJ warnings
- Fix various SonarLint warnings (e.g., the expected/actual args to
Assert.assertEquals() were flipped)
* more sql support for expression array functions
* prepend/slice
* doc fixes
* fix imports
* fix tests
* add null numeric expr for proper conversions between ExprEval and Expr and back to ExprEval
* re-arrange
* imports :(
* add append/prepend test
* array support for expression language for multi-value string columns
* fix tests?
* fixes
* more tests
* fixes
* cleanup
* more better, more test
* ignore inspection
* license
* license fix
* inspection
* remove dumb import
* more better
* some comments
* add expr rewrite for arrayfn args for more magic, tests
* test stuff
* more tests
* fix test
* fix test
* castfunc can deal with arrays
* needs more empty array
* more tests, make cast to long array more forgiving
* refactor
* simplify ExprMacro Expr implementations with base classes in core
* oops
* more test
* use Shuttle for Parser.flatten, javadoc, cleanup
* fixes and more tests
* unused import
* fixes
* javadocs, cleanup, refactors
* fix imports
* more javadoc
* more javadoc
* more
* more javadocs, nonnullbydefault, minor refactor
* markdown fix
* adjustments
* more doc
* move initial filter out
* docs
* map empty arg lambda, apply function argument validation
* check function args at parse time instead of eval time
* more immutable
* more more immutable
* clarify grammar
* fix docs
* empty array is string test, we need a way to make arrays better maybe in the future, or define empty arrays as other types..
* Add state and error tracking for seekable stream supervisors
* Fixed nits in docs
* Made inner class static and updated spec test with jackson inject
* Review changes
* Remove redundant config param in supervisor
* Style
* Applied some of Jon's recommendations
* Add transience field
* write test
* implement code review changes except for reconsidering logic of markRunFinishedAndEvaluateHealth()
* remove transience reporting and fix SeekableStreamSupervisorStateManager impl
* move call to stateManager.markRunFinished() from RunNotice to runInternal() for tests
* remove stateHistory because it wasn't adding much value, some fixes, and add more tests
* fix tests
* code review changes and add HTTP health check status
* fix test failure
* refactor to split into a generic SupervisorStateManager and a specific SeekableStreamSupervisorStateManager
* fixup after merge
* code review changes - add additional docs
* cleanup KafkaIndexTaskTest
* add additional documentation for Kinesis indexing
* remove unused throws class
Recently we've been talking about using SegmentIds as map keys rather than
DataSegments, because its sense of equality is more well-defined. This is
a refactor that does this in the druid-sql module, which mostly involves
DruidSchema and some related classes. It should have no user-visible effects.
* Add checkstyle for "Local variable names shouldn't start with capital"
* Adjust some local variables to constants
* Replace StringUtils.LINE_SEPARATOR with System.lineSeparator()
* Bump Checkstyle to 8.20
Moderate severity vulnerability that affects:
com.puppycrawl.tools:checkstyle
Checkstyle prior to 8.18 loads external DTDs by default,
which can potentially lead to denial of service attacks
or the leaking of confidential information.
Affected versions: < 8.18
* Oops, missed one
* Oops, missed a few
Gian Merlino
Rye
Clint Wylie
Jihoon Son
Jonathan Wei
Chi Cao Minh
Atul Mohan
Zhenxiao Luo
Roman Leventov
Benedict Jin
Parag Jain
Fokko Driesprong
Himanshu
SandishKumarHN
Xavier Léauté
Surekha
Artiom Darie
Sashidhar Thallam
Xue Yu
Fokko Driesprong
Clint Wylie
Justin Borromeo
Gian Merlino
Merlin Lee
Xue Yu