* Error handling improvements for frame channels.
Two changes:
1) Send errors down in-memory channels (BlockingQueueFrameChannel) on
failure. This ensures that in situations where a chain of processors
has been set up on a single machine, all processors see the root
cause error. In particular, this means the final processor in the
chain reports the root cause error, which ensures that someone with
a handle to the final processor will get the proper error.
2) Update FrameFileHttpResponseHandler to expect that the final fetch,
rather than being simply empty, is also empty with a special header.
This ensures that the handler is able to tell the difference between
an empty fetch due to being at EOF, and an empty fetch due to a
truncated HTTP response (after the 200 OK and headers are sent down,
but before any content appears).
* Fix tests, imports.
* Checkstyle!
In the current druid code base, we have the interface DataSegmentPusher which allows us to push segments to the appropriate deep storage without the extension being worried about the semantics of how to push too deep storage.
While working on #12262, whose some part of the code will go as an extension, I realized that we do not have an interface that allows us to do basic "write, get, delete, deleteAll" operations on the appropriate deep storage without let's say pulling the s3-storage-extension dependency in the custom extension.
Hence, the idea of StorageConnector was born where the storage connector sits inside the druid core so all extensions have access to it.
Each deep storage implementation, for eg s3, GCS, will implement this interface.
Now with some Jackson magic, we bind the implementation of the correct deep storage implementation on runtime using a type variable.
The Netty pipeline set up by the client can deliver multiple exceptions,
and can deliver chunks even after delivering exceptions. This makes it
difficult to implement HttpResponseHandlers. Looking at existing handler
implementations, I do not see attempts to handle this case, so it's also
a potential source of bugs.
This patch updates the client to track whether an exception was
encountered, and if so, to not call any additional methods on the handler
after exceptionCaught. It also harmonizes exception handling between
exceptionCaught and channelDisconnected.
Refactors the DruidSchema and DruidTable abstractions to prepare for the Druid Catalog.
As we add the catalog, we’ll want to combine physical segment metadata information with “hints” provided by the catalog. This is best done if we tidy up the existing code to more clearly separate responsibilities.
This PR is purely a refactoring move: no functionality changed. There is no difference to user functionality or external APIs. Functionality changes will come later as we add the catalog itself.
DruidSchema
In the present code, DruidSchema does three tasks:
Holds the segment metadata cache
Interfaces with an external schema manager
Acts as a schema to Calcite
This PR splits those responsibilities.
DruidSchema holds the Calcite schema for the druid namespace, combining information fro the segment metadata cache, from the external schema manager and (later) from the catalog.
SegmentMetadataCache holds the segment metadata cache formerly in DruidSchema.
DruidTable
The present DruidTable class is a bit of a kitchen sink: it holds all the various kinds of tables which Druid supports, and uses if-statements to handle behavior that differs between types. Yet, any given DruidTable will handle only one such table type. To more clearly model the actual table types, we split DruidTable into several classes:
DruidTable becomes an abstract base class to hold Druid-specific methods.
DatasourceTable represents a datasource.
ExternalTable represents an external table, such as from EXTERN or (later) from the catalog.
InlineTable represents the internal case in which we attach data directly to a table.
LookupTable represents Druid’s lookup table mechanism.
The new subclasses are more focused: they can be selective about the data they hold and the various predicates since they represent just one table type. This will be important as the catalog information will differ depending on table type and the new structure makes adding that logic cleaner.
DatasourceMetadata
Previously, the DruidSchema segment cache would work with DruidTable objects. With the catalog, we need a layer between the segment metadata and the table as presented to Calcite. To fix this, the new SegmentMetadataCache class uses a new DatasourceMetadata class as its cache entry to hold only the “physical” segment metadata information: it is up to the DruidTable to combine this with the catalog information in a later PR.
More Efficient Table Resolution
Calcite provides a convenient base class for schema objects: AbstractSchema. However, this class is a bit too convenient: all we have to do is provide a map of tables and Calcite does the rest. This means that, to resolve any single datasource, say, foo, we need to cache segment metadata, external schema information, and catalog information for all tables. Just so Calcite can do a map lookup.
There is nothing special about AbstractSchema. We can handle table lookups ourselves. The new AbstractTableSchema does this. In fact, all the rest of Calcite wants is to resolve individual tables by name, and, for commands we don’t use, to provide a list of table names.
DruidSchema now extends AbstractTableSchema. SegmentMetadataCache resolves individual tables (and provides table names.)
DruidSchemaManager
DruidSchemaManager provides a way to specify table schemas externally. In this sense, it is similar to the catalog, but only for datasources. It originally followed the AbstractSchema pattern: it implements provide a map of tables. This PR provides new optional methods for the table lookup and table names operations. The default implementations work the same way that AbstractSchema works: we get the entire map and pick out the information we need. Extensions that use this API should be revised to support the individual operations instead. Druid code no longer calls the original getTables() method.
The PR has one breaking change: since the DruidSchemaManager map is read-only to the rest of Druid, we should return a Map, not a ConcurrentMap.
* Frame processing and channels.
Follow-up to #12745. This patch adds three new concepts:
1) Frame channels are interfaces for doing nonblocking reads and writes
of frames.
2) Frame processors are interfaces for doing nonblocking processing of
frames received from input channels and sent to output channels.
3) Cluster-by keys, which can be used for sorting or partitioning.
The patch also adds SuperSorter, a user of these concepts, both to
illustrate how they are used, and also because it is going to be useful
in future work.
Central classes:
- ReadableFrameChannel. Implementations include
BlockingQueueFrameChannel (in-memory channel that implements both interfaces),
ReadableFileFrameChannel (file-based channel),
ReadableByteChunksFrameChannel (byte-stream-based channel), and others.
- WritableFrameChannel. Implementations include BlockingQueueFrameChannel
and WritableStreamFrameChannel (byte-stream-based channel).
- ClusterBy, a sorting or partitioning key.
- FrameProcessor, nonblocking processor of frames. Implementations include
FrameChannelBatcher, FrameChannelMerger, and FrameChannelMuxer.
- FrameProcessorExecutor, an executor service that runs FrameProcessors.
- SuperSorter, a class that uses frame channels and processors to
do parallel external merge sort of any amount of data (as long as there
is enough disk space).
* Additional tests, fixes.
* Changes from review.
* Better implementation for ReadableInputStreamFrameChannel.
* Rename getFrameFileReference -> newFrameFileReference.
* Add InterruptedException to runIncrementally; add more tests.
* Cancellation adjustments.
* Review adjustments.
* Refactor BlockingQueueFrameChannel, rename doneReading and doneWriting to close.
* Additional changes from review.
* Additional changes.
* Fix test.
* Adjustments.
* Adjustments.
* Refactor Guice initialization
Builders for various module collections
Revise the extensions loader
Injector builders for server startup
Move Hadoop init to indexer
Clean up server node role filtering
Calcite test injector builder
* Revisions from review comments
* Build fixes
* Revisions from review comments
* Improved Java 17 support and Java runtime docs.
1) Add a "Java runtime" doc page with information about supported
Java versions, garbage collection, and strong encapsulation..
2) Update asm and equalsverifier to versions that support Java 17.
3) Add additional "--add-opens" lines to surefire configuration, so
tests can pass successfully under Java 17.
4) Switch openjdk15 tests to openjdk17.
5) Update FrameFile to specifically mention Java runtime incompatibility
as the cause of not being able to use Memory.map.
6) Update SegmentLoadDropHandler to log an error for Errors too, not
just Exceptions. This is important because an IllegalAccessError is
encountered when the correct "--add-opens" line is not provided,
which would otherwise be silently ignored.
7) Update example configs to use druid.indexer.runner.javaOptsArray
instead of druid.indexer.runner.javaOpts. (The latter is deprecated.)
* Adjustments.
* Use run-java in more places.
* Add run-java.
* Update .gitignore.
* Exclude hadoop-client-api.
Brought in when building on Java 17.
* Swap one more usage of java.
* Fix the run-java script.
* Fix flag.
* Include link to Temurin.
* Spelling.
* Update examples/bin/run-java
Co-authored-by: Xavier Léauté <xl+github@xvrl.net>
Co-authored-by: Xavier Léauté <xl+github@xvrl.net>
Sysmonitor stats (mem, fs, disk, net, cpu, swap, sys, tcp) are reported by all Druid processes, including Peons that are ephemeral in nature. Since Peons always run on the same host as the MiddleManager that spawned them and is unlikely to change, the SyMonitor metrics emitted by Peon are merely duplicates. This is often not a problem except when machines are super-beefy. Imagine a 64-core machine and 32 workers running on this machine. now you will have each Peon reporting metrics for each core. that's an increase of (32 * 64)x in the number of metrics. This leads to a metric explosion.
This PR updates MetricsModule to check node role running while registering SysMonitor and not to load any existing SysMonitor$Stats.
Few indexing tasks register RealtimeMetricsMonitor or TaskRealtimeMetricsMonitor with the process’s MonitorScheduler when they start. These monitors never unregister themselves (they always return true, they'd need to return false to unregister). Each of these monitors emits a set of metrics once every druid.monitoring.emissionPeriod.
As a result, after executing several tasks for a while, Indexer emits metrics of these tasks even after they're long gone.
Proposed Solution
Since one should be able to obtain the last round of ingestion metrics after the task unregisters the monitor, introducing lastRoundMetricsToBePushed variable to keep track of the same and overriding the AbstractMonitor.monitor method in RealtimeMetricsMonitor, TaskRealtimeMetricsMonitor to implement the new logic.
* fix bug in ObjectFlatteners.toMap which caused null values in avro-stream/avro-ocf/parquet/orc to be converted to {} instead of null
* fix parquet test that expected wrong behavior, my bad heh
* Frame format for data transfer and short-term storage.
As we move towards query execution plans that involve more transfer
of data between servers, it's important to have a data format that
provides for doing this more efficiently than the options available to
us today.
This patch adds:
- Columnar frames, which support fast querying.
- Row-based frames, which support fast sorting via memory comparison
and fast whole-row copies via memory copying.
- Frame files, a container format that can be stored on disk or
transferred between servers.
The idea is we should use row-based frames when data is expected to
be sorted, and columnar frames when data is expected to be queried.
The code in this patch is not used in production yet. Therefore, the
patch involves minimal changes outside of the org.apache.druid.frame
package. The main ones are adjustments to SqlBenchmark to add benchmarks
for queries on frames, and the addition of a "forEach" method to Sequence.
* Fixes based on tests, static analysis.
* Additional fixes.
* Skip DS mapping tests on JDK 14+
* Better JDK checking in tests.
* Fix imports.
* Additional comment.
* Adjustments from code review.
* Update test case.
* jvm gc to mxbeans
* add zgc and shenandoah #12476
* remove tryCreateGcCounter
* separate the space collector
* blend GcGenerationCollector into GcCollector
* add jdk surefire argLine
* Add EIGHT_HOUR into possible list of Granularities.
* Add the missing definition.
* fix test.
* Fix another test.
* Stylecheck finally passed.
Co-authored-by: Didip Kerabat <didip@apple.com>
* Mid-level service client and updated high-level clients.
Our servers talk to each other over HTTP. We have a low-level HTTP
client (HttpClient) that is super-asynchronous and super-customizable
through its handlers. It's also proven to be quite robust: we use it
for Broker -> Historical communication over the wide variety of query
types and workloads we support.
But the low-level client has no facilities for service location or
retries, which means we have a variety of high-level clients that
implement these in their own ways. Some high-level clients do a better
job than others. This patch adds a mid-level ServiceClient that makes
it easier for high-level clients to be built correctly and harmoniously,
and migrates some of the high-level logic to use ServiceClients.
Main changes:
1) Add ServiceClient org.apache.druid.rpc package. That package also
contains supporting stuff like ServiceLocator and RetryPolicy
interfaces, and a DiscoveryServiceLocator based on
DruidNodeDiscoveryProvider.
2) Add high-level OverlordClient in org.apache.druid.rpc.indexing.
3) Indexing task client creator in TaskServiceClients. It uses
SpecificTaskServiceLocator to find the tasks. This improves on
ClientInfoTaskProvider by caching task locations for up to 30 seconds
across calls, reducing load on the Overlord.
4) Rework ParallelIndexSupervisorTaskClient to use a ServiceClient
instead of extending IndexTaskClient.
5) Rework RemoteTaskActionClient to use a ServiceClient instead of
DruidLeaderClient.
6) Rework LocalIntermediaryDataManager, TaskMonitor, and
ParallelIndexSupervisorTask. As a result, MiddleManager, Peon, and
Overlord no longer need IndexingServiceClient (which internally used
DruidLeaderClient).
There are some concrete benefits over the prior logic, namely:
- DruidLeaderClient does retries in its "go" method, but only retries
exactly 5 times, does not sleep between retries, and does not retry
retryable HTTP codes like 502, 503, 504. (It only retries IOExceptions.)
ServiceClient handles retries in a more reasonable way.
- DruidLeaderClient's methods are all synchronous, whereas ServiceClient
methods are asynchronous. This is used in one place so far: the
SpecificTaskServiceLocator, so we don't need to block a thread trying
to locate a task. It can be used in other places in the future.
- HttpIndexingServiceClient does not properly handle all server errors.
In some cases, it tries to parse a server error as a successful
response (for example: in getTaskStatus).
- IndexTaskClient currently makes an Overlord call on every task-to-task
HTTP request, as a way to find where the target task is. ServiceClient,
through SpecificTaskServiceLocator, caches these target locations
for a period of time.
* Style adjustments.
* For the coverage.
* Adjustments.
* Better behaviors.
* Fixes.
* Poison StupidPool and fix resource leaks
There are various resource leaks from test setup as well as some
corners in query processing. We poison the StupidPool to start failing
tests when the leaks come and fix any issues uncovered from that so
that we can start from a clean baseline.
Unfortunately, because of how poisoning works,
we can only fail future checkouts from the same pool,
which means that there is a natural race between a
leak happening -> GC occurs -> leak detected -> pool poisoned.
This race means that, depending on interleaving of tests,
if the very last time that an object is checked out
from the pool leaks, then it won't get caught.
At some point in the future, something will catch it,
however and from that point on it will be deterministic.
* Remove various things left over from iterations
* Clean up FilterAnalysis and add javadoc on StupidPool
* Revert changes to .idea/misc.xml that accidentally got pushed
* Style and test branches
* Stylistic woes
In a heterogeneous environment, sometimes you don't have control over the input folder. Upstream can put any folder they want. In this situation the S3InputSource.java is unusable.
Most people like me solved it by using Airflow to fetch the full list of parquet files and pass it over to Druid. But doing this explodes the JSON spec. We had a situation where 1 of the JSON spec is 16MB and that's simply too much for Overlord.
This patch allows users to pass {"filter": "*.parquet"} and let Druid performs the filtering of the input files.
I am using the glob notation to be consistent with the LocalFirehose syntax.
This commit contains the cleanup needed for the new integration test framework.
Changes:
- Fix log lines, misspellings, docs, etc.
- Allow the use of some of Druid's "JSON config" objects in tests
- Fix minor bug in `BaseNodeRoleWatcher`
* Remove null and empty fields from native queries
* Test fixes
* Attempted IT fix.
* Revisions from review comments
* Build fixes resulting from changes suggested by reviews
* IT fix for changed segment size
The web-console (indirectly) calls the Overlord’s GET tasks API to fetch the tasks' summary which in turn queries the metadata tasks table. This query tries to fetch several columns, including payload, of all the rows at once. This introduces a significant memory overhead and can cause unresponsiveness or overlord failure when the ingestion tab is opened multiple times (due to several parallel calls to this API)
Another thing to note is that the task table (the payload column in particular) can be very large. Extracting large payloads from such tables can be very slow, leading to slow UI. While we are fixing the memory pressure in the overlord, we can also fix the slowness in UI caused by fetching large payloads from the table. Fetching large payloads also puts pressure on the metadata store as reported in the community (Metadata store query performance degrades as the tasks in druid_tasks table grows · Issue #12318 · apache/druid )
The task summaries returned as a response for the API are several times smaller and can fit comfortably in memory. So, there is an opportunity here to fix the memory usage, slow ingestion, and under-pressure metadata store by removing the need to handle large payloads in every layer we can. Of course, the solution becomes complex as we try to fix more layers. With that in mind, this page captures two approaches. They vary in complexity and also in the degree to which they fix the aforementioned problems.
The "exceptionCaught" handler may get called multiple times. We should
only return the channel to the pool the first time. Returning it more
than once leads to a warning like "Resource at key[%s] was returned
multiple times?"
* Direct UTF-8 access for "in" filters.
Directly related:
1) InDimFilter: Store stored Strings (in ValuesSet) plus sorted UTF-8
ByteBuffers (in valuesUtf8). Use valuesUtf8 whenever possible. If
necessary, the input set is copied into a ValuesSet. Much logic is
simplified, because we always know what type the values set will be.
I think that there won't even be an efficiency loss in most cases.
InDimFilter is most frequently created by deserialization, and this
patch updates the JsonCreator constructor to deserialize
directly into a ValuesSet.
2) Add Utf8ValueSetIndex, which InDimFilter uses to avoid UTF-8 decodes
during index lookups.
3) Add unsigned comparator to ByteBufferUtils and use it in
GenericIndexed.BYTE_BUFFER_STRATEGY. This is important because UTF-8
bytes can be compared as bytes if, and only if, the comparison
is unsigned.
4) Add specialization to GenericIndexed.singleThreaded().indexOf that
avoids needless ByteBuffer allocations.
5) Clarify that objects returned by ColumnIndexSupplier.as are not
thread-safe. DictionaryEncodedStringIndexSupplier now calls
singleThreaded() on all relevant GenericIndexed objects, saving
a ByteBuffer allocation per access.
Also:
1) Fix performance regression in LikeFilter: since #12315, it applied
the suffix matcher to all values in range even for type MATCH_ALL.
2) Add ObjectStrategy.canCompare() method. This fixes LikeFilterBenchmark,
which was broken due to calls to strategy.compare in
GenericIndexed.fromIterable.
* Add like-filter implementation tests.
* Add in-filter implementation tests.
* Add tests, fix issues.
* Fix style.
* Adjustments from review.
* Ensure ByteBuffers allocated in tests get freed.
Many tests had problems where a direct ByteBuffer would be allocated
and then not freed. This is bad because it causes flaky tests.
To fix this:
1) Add ByteBufferUtils.allocateDirect(size), which returns a ResourceHolder.
This makes it easy to free the direct buffer. Currently, it's only used
in tests, because production code seems OK.
2) Update all usages of ByteBuffer.allocateDirect (off-heap) in tests either
to ByteBuffer.allocate (on-heap, which are garbaged collected), or to
ByteBufferUtils.allocateDirect (wherever it seemed like there was a good
reason for the buffer to be off-heap). Make sure to close all direct
holders when done.
* Changes based on CI results.
* A different approach.
* Roll back BitmapOperationTest stuff.
* Try additional surefire memory.
* Revert "Roll back BitmapOperationTest stuff."
This reverts commit 49f846d9e3.
* Add TestBufferPool.
* Revert Xmx change in tests.
* Better behaved NestedQueryPushDownTest. Exit tests on OOME.
* Fix TestBufferPool.
* Remove T1C from ARM tests.
* Somewhat safer.
* Fix tests.
* Fix style stuff.
* Additional debugging.
* Reset null / expr configs better.
* ExpressionLambdaAggregatorFactory thread-safety.
* Alter forkNode to try to get better info when a JVM crashes.
* Fix buffer retention in ExpressionLambdaAggregatorFactory.
* Remove unused import.
Allow a Druid cluster to kill segments whose interval_end is a date in the future. This can be done by setting druid.coordinator.kill.durationToRetain to a negative period. For example PT-24H would allow segments to be killed if their interval_end date was 24 hours or less into the future at the time that the kill task is generated by the system.
A cluster operator can also disregard the druid.coordinator.kill.durationToRetain entirely by setting a new configuration, druid.coordinator.kill.ignoreDurationToRetain=true. This ignores interval_end date when looking for segments to kill, and instead is capable of killing any segment marked unused. This new configuration is off by default, and a cluster operator should fully understand and accept the risks if they enable it.
* GroupBy: Reduce allocations by reusing entry and key holders.
Two main changes:
1) Reuse Entry objects returned by various implementations of
Grouper.iterator.
2) Reuse key objects contained within those Entry objects.
This is allowed by the contract, which states that entries must be
processed and immediately discarded. However, not all call sites
respected this, so this patch also updates those call sites.
One particularly sneaky way that the old code retained entries too long
is due to Guava's MergingIterator and CombiningIterator. Internally,
these both advance to the next value prior to returning the current
value. So, this patch addresses that in two ways:
1) For merging, we have our own implementation MergeIterator already,
although it had the same problem. So, this patch updates our
implementation to return the current item prior to advancing to the
next item. It also adds a forbidden-api entry to ensure that this
safer implementation is used instead of Guava's.
2) For combining, we address the problem in a different way: by copying
the key when creating the new, combined entry.
* Attempt to fix test.
* Remove unused import.
* DimensionRangeShardSpec speed boost.
Calling isEmpty() and equals() on RangeSets is expensive, because these
fall back on default implementations that call size(). And size() is
_also_ a default implementation that iterates the entire collection.
* Fix and test from code review.
* Reduce allocations due to Jackson serialization.
This patch attacks two sources of allocations during Jackson
serialization:
1) ObjectMapper.writeValue and JsonGenerator.writeObject create a new
DefaultSerializerProvider instance for each call. It has lots of
fields and creates pressure on the garbage collector. So, this patch
adds helper functions in JacksonUtils that enable reuse of
SerializerProvider objects and updates various call sites to make
use of this.
2) GroupByQueryToolChest copies the ObjectMapper for every query to
install a special module that supports backwards compatibility with
map-based rows. This isn't needed if resultAsArray is set and
all servers are running Druid 0.16.0 or later. This release was a
while ago. So, this patch disables backwards compatibility by default,
which eliminates the need to copy the heavyweight ObjectMapper. The
patch also introduces a configuration option that allows admins to
explicitly enable backwards compatibility.
* Add test.
* Update additional call sites and add to forbidden APIs.
* JvmMonitor: Handle more generation and collector scenarios.
ZGC on Java 11 only has a generation 1 (there is no 0). This causes
a NullPointerException when trying to extract the spacesCount for
generation 0. In addition, ZGC on Java 15 has a collector number 2
but no spaces in generation 2, which breaks the assumption that
collectors always have same-numbered spaces.
This patch adjusts things to be more robust, enabling the JvmMonitor
to work properly for ZGC on both Java 11 and 15.
* Test adjustments.
* Improve surefire arglines.
* Need a placeholder
This PR enables ARM builds on Travis. I've ported over the changes from @martin-g on reducing heap requirements for some of the tests to ensure they run well on Travis arm instances.
GCP allows bucket names to contain underscores. When a location in such a bucket
is mapped to `java.net.URI`, `URI.getHost()` returns null. `URI.getHost()` is used as
the bucket name in `CloudObjectLocation`, leading to an NPE.
This commit uses `URI.getAuthority()` as the bucket name if `URI.getHost()` is null.
* Make tombstones ingestible by having them return an empty result set.
* Spotbug
* Coverage
* Coverage
* Remove unnecessary exception (checkstyle)
* Fix integration test and add one more to test dropExisting set to false over tombstones
* Force dropExisting to true in auto-compaction when the interval contains only tombstones
* Checkstyle, fix unit test
* Changed flag by mistake, fixing it
* Remove method from interface since this method is specific to only DruidSegmentInputentity
* Fix typo
* Adapt to latest code
* Update comments when only tombstones to compact
* Move empty iterator to a new DruidTombstoneSegmentReader
* Code review feedback
* Checkstyle
* Review feedback
* Coverage
If there are many shards, mapper of IndexGeneratorJob seems to spend a lot of time in calling
DimensionRangeShardSpec.isInChunk to lookup target shard. This can be significantly improved
by using binary search instead of comparing an input row to every shardSpec.
Changes:
* Add `BaseDimensionRangeShardSpec` which provides a binary-search-based
implementation for `createLookup`
* `DimensionRangeShardSpec`, `SingleDimensionShardSpec`, and
`DimensionRangeBucketShardSpec` now extend `BaseDimensionRangeShardSpec`
* add impl
* add impl
* fix checkstyle
* add impl
* add unit test
* fix stuff
* fix stuff
* fix stuff
* add unit test
* add more unit tests
* add more unit tests
* add IT
* add IT
* add IT
* add IT
* add ITs
* address comments
* fix test
* fix test
* fix test
* address comments
* address comments
* address comments
* fix conflict
* fix checkstyle
* address comments
* fix test
* fix checkstyle
* fix test
* fix test
* fix IT
* Counting nulls in String cardinality with a config
* Adding tests for the new config
* Wrapping the vectorize part to allow backward compatibility
* Adding different tests, cleaning the code and putting the check at the proper position, handling hasRow() and hasValue() changes
* Updating testcase and code
* Adding null handling test to improve coverage
* Checkstyle fix
* Adding 1 more change in docs
* Making docs clearer
Gian Merlino
Karan Kumar
Paul Rogers
Clint Wylie
Tejaswini Bandlamudi
Maytas Monsereenusorn
Frank Chen
Jianhuan Liu
Didip Kerabat
imply-cheddar
Rui Chen
AmatyaAvadhanula
Lucas Capistrant
Gian Merlino
Frank Chen
Abhishek Agarwal
Will Xu
Agustin Gonzalez
hqx871
Jihoon Son
somu-imply