ChangeLog

# 2026-10-15 [version 1.16.3]
## 🐣 New Features
- Add min/max BKey static field in v2 APIs

## ⚙️ Internal Changes
- Move result decoding off the IO thread in v2 APIs
- Add dependabot.yml to check in develop branch
- Enable all ASCII command features when connected to Arcus Proxy

## 🐛 Bug Fixes
- Correct version flag used to build gets operation in v2 APIs
- Verify correct byte length and not expose origin data object in BKey in v2 APIs
- Preserve initial connection observers during `ArcusClient` initialization
- Isolate connection observer exceptions
- Skip remove if nodeSet return null when already node removed by same hash point

## ⬆️ Dependency Upgrades
- Update jackson-databind version to 2.22.1
- Update log4j-api version to 2.25.5

# 2026-08-04 [version 1.16.2]
## 🐣 New Features
- Add beta version of CompletableFuture(v2) APIs
- Add pluggable compression codec support with Snappy algorithm
- Remove deprecated SMGetMode class

## ⚙️ Internal Changes
- Add isForceSerializeForCollection method to Transcoder
- Do not skip decompress even if collection transcoder
- Reuse callback instance for repeated Op creation
- Unify BKey, EFlag naming
- Unify OperationCallback patterns
- Replace assert statements with proper exception handling
- Align code style settings with checkstyle rules
- Updated the devtools/maketags.sh
- Separate CollectionAttributes into CreateAttributes, SetAttributes, ItemAttributes, UpdateAttributes to support long type exptime in v2 apis

## 🐛 Bug Fixes
- Remove Concurrency problem in locator allNodes
- Add null/empty string behavior for the flush prefix argument
- Prevent NoSuchMethodError in TouchOperationImpl

## 📝 Documentation
- Update JDK requirements in README
- Update ConnectionFactoryBuilder docs
- Use correct limit validation for compValue

## ⬆️ Dependency Upgrades
- Update log4j-core version to 2.25.4
- Update jackson-databind version to 2.22.0

# 2026-04-29 [version 1.16.1]
## 🐛 Bug Fixes
  - Use ScramSaslClientFactory only in SASL Authentication

# 2026-02-09 [version 1.16.0]
## 🐣 New Features
  - Support JsonSerializingTranscoder, GenericJsonSerializingTranscoder
  - Support SASL Authentication for ASCII/Binary protocol
  - Support get and touch (GAT) command
  - Support shard key for ketama hashing
  - Add set/get replica methods to distribute read traffic for hot items
  - Removed some deprecated methods. (old smget, asyncSetBulk, ...)
  - Remove timeoutRatioThreshold option.
  - Deprecate `SMGetMode` enum type and `setMaxSMGetKeyChunkSize` method.
## 🔧 Enhancements
  - Enhance version operation logic after connection established
  - Enhance handling InputQ and WriteQ after connection lost when MemcachedNode needs auth process
  - Allow queuing operations on nodes going to immediately reconnect
  - Enhance ConnectionObserver logic
## ⚙️ Internal Changes
  - Add `@Nullable` annotation to `CollectionDelete#getAdditionalArgs()`
  - Use more proper key separator for multi-keyed collection operations
  - Move checkDupKey method into KeyValidator
  - Increase default value of timeoutDurationThreshold from 1000ms to 1600ms
  - Call offer() instead of add() for addedQueue
## 🐛 Bug Fixes
  - Reset the use of mget, mgets, " " separator, version info when connection is lost
  - Check if writeQ is empty before move its operations to reconnectBlocked
  - Remove infinite loop in attemptReconnects()
  - Fix bug for ConnectionObserver
  - Split piped operations into single-key and multi-key to resolve bug during migration
  - Call correct method for overloaded asyncBopUpsert method
## 📝 Documentation
  - Fix docs link references
## ✅ Testing
  - Add printing docker logs on `docker compose up -d` failure
  - Fix example for some APIs
## ⬆️ Dependency Upgrades
  - Upgrade log4j version to 2.25.3.

# 2025-09-22 [version 1.15.0]
## 🐣 New Features
  - Add touch command to update item expiration
  - Deprecate CollectionGetBulkFuture#getOperationStatus
  - Deprecate CollectionTranscoder
## 🔧 Enhancements
  - Add try-catch and error logging in callback methods called by ZooKeeper thread
  - Throw IllegalStateException instead of RuntimeException in AuthThread constructor
  - Change auth messages of binary sasl operations
  - Lower log level to info in matchStatus()
  - Make piped insert operations process synchronously
  - Make sure MultiOperationCallback is threadsafe
  - Use direct buffers in TCPMemcachedNodeImpl
  - Make refineTrimmedKeys easier to understand
  - Set OperationStatus even if already CANCELED status exists
  - Throw CancellationException when cancelled
## ⚙️ Internal Changes
  - Use try-with-resources in serialize/deserialize
  - Merge KV and collection transcoders
  - Move exception message logic into each exception class
  - Refactor common constants and methods into TranscoderUtils
  - Extract compression logic from BaseSerializingTranscoder
## 🐛 Bug Fixes
  - Use `conn.getLocator()` instead of `conn.getLocator().getReadonlyCopy()` for `MemcachedClient#getFlushNodes()` method
  - Do not modify UnmodifiableList object while validating replication group addresses
  - Use enabledMGetsOp in asyncGetsBulk method
  - Add new StatusCode `ERR_FAILED_END` and return it when piped collection operation is failed
  - Make matchStatus covers all responses
  - Send ERR_INTERNAL status when pipe error occurred
  - Do not cancel when command is completing in handleLine()
## 📝 Documentation
  - Add description for touch API
  - Add description for `CANCELED` OperationStatus when an operation is cancelled
  - Remove the usage example of deprecated class, CollectionTranscoder
  - Declare version 1.14.1 as unstable to connect to replication server
## ✅ Testing
  - Tidy ConnectionFactoryBuilderTest
  - Use assertInstanceOf in ConnectionFactoryBuilderTest
  - Use ConnectionFactoryBuilder instead of CFB for test code
  - Handle when the state is set after cancellation in CancelFutureTest
  - Assert only if cancel succeed

# 2025-05-09 [version 1.14.1] (Unstable to connect to replication server)
## 🐣 New Features
  - Add node information into OperationException.
  - Add option to disable optimization in CollectionTranscoder.
  - Deprecate old smget API.
  - Make ArcusClientIF extends MemcachedClientIF.
  - Make waitForQueues method into private.
  - Make getApiReadPriority method in ConnectionFactory returns ReadPriority.
  - Override equals and hashCode methods in value classes.
  - Remove deprecated repl setter in ConnectionFactoryBuilder.
  - Return partial result if error or cancel occurred in getSome method.
  - Return CompositeException in get method in BulkGetFuture.
  - Return empty map if response is NOT_FOUND_ELEMENT in BopFindPositionWithGet API.
  - Support custom classloader in transcoder when deserializing.
  - Support JDK 21 by suppressing warnings.
  - Support for checkstyle versions 8.42 and higher.
  - Supports INVALID responses that do not require reconnection.
  - Throw exception when wrong argument came into ConnectionFactoryBuilder.
## 🔧 Enhancements
  - Change cacheList and alterList parsing logic.
  - Change some assert statement into IllegalArgumentException or Assertions methods.
  - Encodes only elements after nextOpIndex, not the entire element.
  - Optimize switch-over and updateReplConnections logics.
  - Optimize variable data types in futures.
## ⚙️ Internal Changes
  - Choose get/mget by version when optimize get commands and limit key count 100.
  - Log unexpected events received from ZooKeeper watcher.
  - Read bytes from ARCUS while PIPE_ERROR received in the pipe operation.
  - Remove wasCancelled() method.
## 🐛 Bug Fixes
  - Apply appropriate synchronization on fields of SMGetResult class.
  - Do not send write op to slave node.
  - Handling various switchover cases.
  - Send flush op to master node only.
  - Set StatusCode in CollectionOperationStatus.
  - Use proper index when lop piped insert.
  - Call receivedStatus callback in OperationImpl#handleError method.
  - Return CANCELED status when getOperationStatus called.
## 📝 Documentation
  - Add backslash before `<`, `>`.
  - Separate front cache docs.
  - Update ChangeLog format to be more readable.
  - Update ConnectionFactoryBuilder docs.
## ✅ Testing
  - Add test case for Pipe API when it's non-piped.
  - Add test case for `MemcachedConnection.handleCacheNodesChange()` method in replication mode.
  - Fix CI test failures.
  - Fix test cases which could be failed sometimes.
  - Update jdk ci version and ubuntu version.
## ⬆️ Dependency Upgrades
  - Upgrade ehcache version to 3.10.8.
  - Upgrade JUnit version to 5.10.2, JMock version to 2.13.1.

# 2024-07-31 [version 1.14.0]
## 🐣 New Features
  - Bulk methods using varargs keys are deprecated. Instead, methods using collection keys are still available.
  - ArcusClient factory methods without zookeeper address are deprecated.
  - Provide shutdown(long, TimeUnit) method for ArcusClient.
  - Add auto import setting.
  - Add DNS cache TTL verification.
  - Add ArcusClient factory methods without ConnectionFactoryBuilder.
  - Add async mop upsert method.
## 🔧 Enhancements
  - Add connection information and elapsed time into TimeoutException message.
  - Add all operations at once in broadcast methods.
  - Return GetFuture instead of OperationFuture in asyncGets method.
  - Use GetResult class instead of setting results into future directly in collection get methods.
  - Use List#sublist method instead of using nested collection when split operations in bulk methods.
  - Refactor redundant concurrent data structure and unnecessary modifier.
  - Change the way ArcusClient is named.
  - Change MBean name of ArcusClient to make more readable.
  - Remove Transcoder argument in LocalCacheManager.
  - Remove unused methods/variables and redundant generic type.
  - Remove unused TimeoutException constructors.
  - Remove TranscoderService field in MemcachedClient and BulkService properties in ConnectionFactoryBuilder.
    Decoding value with transcoder will be done in user thread, such as tomcat thread.
## 🐛 Bug Fixes
  - Make different results from InetSocketAddress.toString() same across JDK versions
  - Throw exception when bop get bulk count is lower than 1.
  - Fix invalid isTimeout value when creating BulkGetFuture with another object.
  - Set default value of shouldOptimize to false in DefaultConnectionFactory.
  - Consider optimizedOp when drain all of operations from the writeQ.
  - Make sure to create readonly copy of locator that has same shape with original one.
## 📝 Documentation
  - Fix wrong information.
  - Add DNS cache TTL information.
  - Add mop upsert API description.
## ✅ Testing
  - Upgrade CI setup python version to 2.7.
  - Use docker compose in CI tests.
  - Fix various test cases which could be failed sometimes.
  - Stop CI test when at least one test fails.
## ⬆️ Dependency Upgrades
  - Upgrade Java version to 8.
  - Upgrade log4j version to 2.23.1.
  - Upgrade slf4j version to 2.0.12.

2023-09-25 [version 1.13.4]
	* [FEATURE] shutdown client after all of operations are processed
	* [FEATURE] Prepared the node locator for data migration
	* [FEATURE] Add TCP connection keep-alive option.
	* [ENHANCE] add pool and service code information on timeout message
	* [ENHANCE] Reconnect to ZK when cache_list znode is deleted.
	* [ENHANCE] Enhance MemcachedNode.toString().
	* [ENHANCE] Added a JRE version in client_list znode.
	* [ENHANCE] Optimize groupingKeys() logic
	* [ENHANCE] change put method logic in LocalCacheManager in aysncGet.
	* [ENHANCE] Remove repeating encode logic in CollectionBulkInsert.
	* [ENHANCE] Seperate FrontCacheLogic in asyncGetBulk from MemcachedClient
	            to FrontCacheMemcachedClient.
	* [ENHANCE] Modify decoding logic in collection get api.
	* [ENHANCE] Change decode logic in BTreeGetBulk api.
	* [FIX] get operation can be bulk operation if having multi key.
	* [FIX] removed key field in CollectionBulkInsertOperationImpl.
	* [FIX] Add eflag field in SMGetElement class.
	* [FIX] Fix BTreeSMGetImpl.decodeItemHeader()
	* [FIX] Rollback MultiOperationCallback.
	* [FIX] add pip dependency install
	* [FIX] Add apt-get update command before apt-get install.
	* [FIX] adjust checkstyle to mopDelete()
	* [FIX] Fix buggy code.
	* [FIX] remove duplicate maven dependency caching
	* [FIX] Call Future.get() in test setup.
	* [FIX] Checkstyle violation
	* [FIX] Call Future.get() for fix CI bug.
	* [FIX] Remove unused import.
	* [FIX] Fix operation redirection.
	* [FIX] Not to cancel operations in node that not in cache list but in
	        alter list.
	* [FIX] Fix readQ, writeQ size error.
	* [FIX] Set handling node to print node information in "inactive node"
	        cancel message.
	* [FIX] Fix bug that is occurred when client is attached to Arcus cluster
	        that is doing migration type=LEAVE.
	* [FIX] Modified the count value of CountDownLatch in broadcastOperation.
	* [FIX] Fixed a simple code mistake in processAlterListResult().
	* [FIX] Checked that the new alter node must not be in allNodes.
	* [FIX] Checked that new joining node must not be in allNodes.
	* [FIX] Fixed the logic of locator.getOwnerNode().
	* [FIX] Fix migration JOIN bug.
	* [FIX] Fixed the code of moving the hash range of leaving nodes.
	* [FIX] getVersion method concurrency error.
	* [FIX] size of mergedOpStatus list in pipedCollectionOperation.
	* [FIX] getOperationStatus method in asyncCollectionPipedInsert/Update.
	* [FIX] Element sequence when using asyncLopInsert api.
	* [FIX] Fix isCancelled,cancel method logic in BulkGetFuture.
	* [FIX] change cancel method logic in OperationFuture.
	* [FIX] Change cancel method logic in multi-operation Future.
	* [FIX] Change keyGroup size comparing logic in groupingkeys method.
	* [FIX] Change syncronization tool in getVersion().
	* [FIX] sync problem in BaseOperationImpl cancel and transitionState
	        method.
	* [FIX] Incorrect boolean result in asycn flush() method.
	* [FIX] Infinity waiting with get method in BulkGetFuture.
	* [FIX] getElement logic in BTreeStoreAndGetFuture.
	* [CLEANUP] Added a makeMemcachedNode() called from attachMemcachedNode().
	* [CLEANUP] Added the insertNodeIntoGroup() and removeNodeFromGroup().
	* [CLEANUP] Logged the address of the newly attached alter node.
	* [TEST] Set logger to Log4jLogger when running test.
	* [TEST] Set log level to DEBUG temporarily to dig CI failure issue.
	* [TEST] change python install script in ci.yml.
	* [TEST] fix testcase in PipedBulkInsertSetWithAttrTest.
	* [TEST] Add Socket keepAlive option test.
	* [DOC] Replace "\t" to " ".
	* [DOC] Make example codes more readable.
	* [DOC] fixed the name of async get bulk API in getSome().
	* [DOC] Fixed how to receive the result value of asyncStoreBulk Future.
	* [INTERNAL] Fix compile warnings.
	* [INTERNAL] Prepare BTreeSMGet to clone operations.
	* [INTERNAL] Clone operations to prepare migration.
	* [INTERNAL] add asyncMopDelete method - delete by mkeyList
	* [INTERNAL] add omitted parameter methods - list/set/map
	* [INTERNAL] separate usage of subkey and bkey/mkey
	* [INTERNAL] add omitted parameter method - asyncBopGet()
	* [INTERNAL] Prepare SetPipedExist to redirect in migration.
	* [INTERNAL] Prepare NodeLocator to redirect in migration.
	* [INTERNAL] Redirect to prepare migration.
	* [INTERNAL] Disabled auto join completion and auto leave abort.
	* [INTERNAL] Enhance compile options.
	* [INTERNAL] Remove DEBUG level log for #534
	* [INTERNAL] Prepare to migration.
	* [INTERNAL] Change CI command to detect Checkstyle violation.
	* [INTERNAL] Wait a second before reinit CacheMonitor or MigrationMonitor.
	* [INTERNAL] Reset the continuous timeout if any among piped ops succeeds
	* [INTERNAL] Use last nodes change.
	* [INTERNAL] Overriding idDone() in BulkOperationFuture
	* [INTERNAL] Upgrade ZK Client dependency version from 3.4.14 to 3.5.9
	* [INTERNAL] Add comment in collection get apis.

2022-04-26 [version 1.13.3]
	* [FEATURE] print select delay in case of too many empty selected keys.
	* [FEATURE] shutdown client more gracefully.
	* [FEATURE] add closeChannel interface in MemcachedNode.
	* [FEATURE] apply Github-CI to test client.
	* [FEATURE] return true from isPipeOperation() of
	            CollectionBulkInsertOperationImpl.
	* [FEATURE] add timeout duration threshold.
	* [FEATURE] use System.nanoTime() instead of System.currentTimeMillis()
	            in MemcachedConnection.
	* [FEATURE] prevent duplicate nodes from being added into the reconnect queue.
	* [FEATURE] delayed switchover task from switchover event of zookeeper.
	* [FEATURE] add isIdempotentOperation in Operation interface.
	* [FEATURE] block to use redistribute failure mode in ArcusClient.
	* [FEATURE] add bkey validation.
	* [FEATURE] upgrade log4j version for security vulnerabilities.
	* [FEATURE] support cancel failure mode in mget, mgets operation.
	* [FEATURE] support expanded replication group.
	* [FEATURE] add node version statistics for monitoring mbean
	* [FEATURE] update node statistics when the cache list changes.
	* [FEATURE] throw exception if memcached nodes do not exist at first.
	* [ENHANCE] do switchover task immediately if readQ is empty or
	            node is going to be reconnected.
	* [ENHANCE] Enhance timeout exception message.
	* [ENHANCE] Remove getRepresentKey() and add getMemcachedNode() to
	            BTreeSMGet to skip key iteration for searching MemcachedNode.
	* [ENHANCE] filter duplicated operation from not writeQ but readQ.
	* [ENHANCE] do not rearrange list when removing addresses of changed
	            replicaion groups.
	* [ENHANCE] add the TimeoutException message to broad casting operation.
	* [FIX] set channel to node first before connecting  it in assertion mode.
	* [FIX] change the fast shutdown time.
	* [FIX] fix ConcurrentModificationException in removing entry of reconnect map.
	* [FIX] removed prevAddrMap field to update cachelist correctly.
	* [FIX] resolve ConcurrentModificationException occurs in handleNodesToRemove.
	* [FIX] reset operation state in resend.
	* [FIX] change the order of moveOperation and ChangeRole on switchover.
	* [FIX] remove unnecessary String.valueOf in ArcusClient.asyncMopUpdate.
	* [FIX] CollectionOperationImpl command buffer.
	* [FIX] update node name when switchover.
	* [FIX] fixed long type string to unsigned long type string on bkey.
	* [FIX] Operation command buffer size.
	* [FIX] reset operation state in writing state when moving operations to
	        new master node.
	* [FIX] fixed parsing only one result after switchover in pipe operation.
	* [FIX] add null check in attachment removal of selection key.
	* [FIX] do not create connection pool array if node address is empty.
	* [FIX] on the bulk operation only the timed out operation set the timed out.
	* [CLEANUP] remove socket channel argument in MemcachedNode constructor.
	* [CLEANUP] remove createKeyIfNotExist field and duplicate codes in
	            collection insert classes.
	* [CLEANUP] refactored ReconnectQueue of MemcachedConnection.
	* [CLEANUP] add comment about avoiding ConcurrentModificationException.
	* [CLEANUP] refactored CollectionGet.
	* [CLEANUP] refactored updateReplConnections in MemcachedConnection.
	* [CLEANUP] separate constructor for searching condition.
	* [CLEANUP] refactored bkey.
	* [CLEANUP] isDebugEnabled and isInfoEnabled flag to print debug log.
	* [CLEANUP] refactored get exist bkey.
	* [CLEANUP] fixed the code indentation.
	* [CLEANUP] refactored the method for validating replication group.
	* [CLEANUP] refactored the method to checking switchover.
	* [CLEANUP] refactored the cache list update functions of replication cluster.
	* [CLEANUP] return immutable collection of node and groups.
	* [CLEANUP] re-naming variables and methods in MemcachedConnection more clearly.
	* [CLEANUP] removed readBufferSize argument in MemcachedConnection().
	* [CLEANUP] refactor ArcusClient initialization codes.
	* [CLEANUP] incorrect indentation.
	* [CLEANUP] removed hashAlgorithm argument from ArcusKetamaLocator constructor.
	* [CLEANUP] removed unnecessary log warn message in getAllOperations().
	* [TEST] fix build error in ClientBaseCase test class.
	* [TEST] use assertEquals to check unexpected value from get operation in
	         BulkStoreTest.
	* [DOC] update btree api doc.
	* [DOC] add ci and license badge.
	* [DOC] fixed percent encoding
	* [DOC] add description of collection attribute.
	* [DOC] add the precaution about character encoding.
	* [DOC] Update docs (fix typo, fix outdated code sample). 
	* [DOC] add jdk requirements to README.md.
	* [DOC] fix invalid javadoc param.

2021-05-08 [version 1.13.2]
	* [FIX] do not use default transcoder.

2021-05-04 [version 1.13.1]
	* [FIX] support library backward compatibility for arcus-spring
	* [FIX] fix compatibility with Java 6, 7, 8 for ByteBuffer
	* [TEST] fix sleep time for item to be expired

2021-03-17 [version 1.13.0]
	* [FEATURE] support mgets command.
	* [FEATURE] change return type of kv API. (Future => OperationFuture)
	* [FEATURE] set the max key size to 4000.
	* [FIX] invalid key length in bop mget, smget command.
	* [FIX] cancel sync operations when an exception occurred.
	* [ENHANCE] add node information to the cancellation message.
	* [ENHANCE] add the specific TimeoutException message.
	* [ENHANCE] do not check the op existence in readQ when writing it.
	* [ENHANCE] do not cancel the operations if it is first connecting.
	* [ENHANCE] reflected only the changed groups in hash ring.
	* [CLEANUP] apply whitespace checkstyle.
	* [TEST] bump junit from 4.4 to 4.13.1.
	* [DOC] add the description of future api.
	* [DOC] change the description of the max item size.
	* [DOC] adjust some format to improve doc readability.

2020-08-04 [version 1.12.1]
	* [FEATURE] asyncDeleteBulk
	* [FEATURE] add maven plugin of checkstyle
	* [FEATURE] apply checkstyle
	* [CLEANUP] apply Indentation checkstyle
	* [CLEANUP] apply LineLength checkstyle
	* [CLEANUP] reduce line length in test sources
	* [CLEANUP] reduce line length in client sources
	* [CLEANUP] apply Import checkstyle
	* [CLEANUP] replace tab charcter to space
	* [CLEANUP] remove nested block
	* [CLEANUP] prevent instantiation of utility classes
	* [CLEANUP] remove duplicate code for parsing response of
	            BTreeGetBulkOperation
	* [CLEANUP] merged CollectionUpsertOperation to CollectionStoreOperation
	* [CLEANUP] solve hash point collision with comparison socket address of
	            node
	* [CLEANUP] renamed store to insert of collection
	* [CLEANUP] update comment for collection response format
	* [CLEANUP] change some javadoc comments to use code tag
	* [CLEANUP] don't occur switchover in sop exist operation.
	* [CLEANUP] remove non-javadoc comments
	* [CLEANUP] refactor asyncSetBulk, asyncDeleteBulk
	* [CLEANUP] deprecate bulkService API
	* [CLEANUP] refactored the constructor functions of KetamaNodeLocator.
	* [CLEANUP] refactor the parts that use socketChannel API
	* [CLEANUP] remove the authentication failure log when OperationException
	            occurs
	* [CLEANUP] refactored the handleNodeManageQueue() method
	* [CLEANUP] refactored the attemptReconnects() method
	* [CLEANUP] refactored the ENABLE_REPLICATION code tag
	* [CLEANUP] refactered the updateConnections() method
	* [CLEANUP] separated the updateReplConnections() from the
	            updateConnections()
	* [CLEANUP] moved the selector wakeup code into putMemcachedQueue()
	* [FIX] Canceling the operations if input queue of node is full when moving
	        operations
	* [ENHANCE] destroy read queue of removed node
	* [ENHANCE] do not cancel the operation twice when using authentication in
	            setupResend of TCPMemcachedNodeImpl
	* [TEST] refactor test codes related setUp and tearDown

2020-03-16 [version 1.12.0]
	* [FEATURE] change max element bytes
	* [FIX] ConcurrentModificationException in foreach loop of
	        SelectionKey in handleIO
	* [FIX] May produce NullPointerException when checking
	        the operation has been canceled
	* [ENHANCE] Skip the cancelled operation has not been
	            written to buffer
	* [CLEANUP] convert log4j configuration file format from
	            properties to xml
	* [CLEANUP] convert tab to space in pom.xml
	* [CLEANUP] remove readQ overflow
	* [CLEANUP] refactor version operation handling
	* [CLEANUP] edit getMaxReconnectDelay method comment
	* [TEST] fix travis failed test case when USE_ZK is true
	* [TEST] ignore ConsistentHashingTest
	* [DOC] fix broken link of flush in other API
	* [DOC] update description of logging
	* [DOC] remove bold on link in btree API
	* [OTHER] upgrade log4j version for security vulnerabilities
	* [OTHER] upgrade zookeeper version 3.4.5=>3.4.14

2019-06-05 [version 1.11.5]
	* [FIX] asyncBopIncr,asyncBopDecr command initial range problem
	* [CLEANUP] remove TIMEDOUT state of operation
	* [CLEANUP] remove the limitation of bopGetBulk key size
	* [DOC] Changed ATTR_MISMATCH response description
			according to spec change of 'bop smget'

2018-11-08 [version 1.11.4]
	* [FIX] change FAKE_SERVER_NODE check method
	* [FIX] do not cancel an operation already canceled in setupResend

2018-09-28 [version 1.11.3]
	* [FEATURE] Adding support for SLF4J logging
	* [FIX] Set next operation index of pipedUpdateOp during switchover
	* [ENHANCE] CacheManager thread do not stop until shutdown is requested
	* [TEST] Check unit test exception handling
	* [TEST] Smget test modification for subversion

2018-06-26 [version 1.11.2]
	* [Fix] bulk and pipe operation buffer overhead changed from 64 to 128
	* [Fix] Select separator depending on node version.
	* [ENHANCE] Gen client info string even if an exception occur.
	* [ENHANCE] Print current cache list when reconnect to ZK.
	* [TEST] Fix travis-ci test error due to memcached port conflict.

2018-06-08 [version 1.11.1]
	* [Fix] CacheManager shutdown by exceptions while reconnect ZooKeeper.
	* [FIX] ZkInitLatch countDown bug when reconnect with ZK session timeout.
	* [Fix] Instance version comparsion bug for using MGetOperation.
	* [Fix] ClassCastException error when optimize the new mget operation.
	* [Fix] flush_by_prefix method return false when prefix does not exist.
	* [ENHANCE] throw exception when can't create the znode of client info.
	* [DOC] Describe the differences of old and new smget API.
	* [DOC] Describe that the frontcache is not deleted by the flush command.
	* [OTHER] Adjust code indentation.

2017-09-23 [version 1.11.0] UNSTABLE
	* [Feature] Support long key. MAX_KEY_LENGTH(250 => 32000).
	* [Fix]     Fix the trimmed/duplicated bugs of bop smget.
	* [Enhance] Use space separated keys instead of comma separated keys.
	* [Enhance] Use new mget command of arcus-memcached in asyncGetBulk().
	   - Choose the old get command or the new mget command
	     after checking the version of the connected arcus-memcached server.
	* [Enhance] Divide the getBulk operation by N(=200) keys per node.
	* [UNSTABLE] See the below issues
	   - Issue in version checking mget is compatible with arcus-memcached.
	     - The version check is OK for arcus-memcacehd version 1.10.X.
	     - The version check is preblematic for version 1.9 and below.
	   - ClassCastException error when optimize the new mget operation.
	   - CacheManager stops by reconnect timeout after ZK sesssion timeout.

2017-07-28 [version 1.10.1] UNSTABLE
	* [Fix] Fix connection latch count calculation mistake.
	* [Fix] Fix the asyncBopDecr mistake of ArcusClientPool.
	* [Fix] Add the missed response handling in asyncBopExtendedGet.
	   - Add default handling for error response such as OUT_OF_RANGE.
	* [Feature] Add the validation checking on prefix string.
	* [Enhance] Add the time unit in operation timeout messages.
	* [UNSTABLE] See the below issues
	   - CacheManager stops by reconnect timeout after ZK sesssion timeout.

2017-03-24 [version 1.10.0] UNSTABLE
	* [Feature] Add a map collection type.
	* [Cleanup] Separate CacheMonitor ZK watcher from CacheManager.
	* [Cleanup] Refactor method call of updateConnection to task execution.
	* [Cleanup] Combine timeout tests into a single test.
	* [Cleanup] Remove duplicate test codes.
	* [Test] Add unit tests for SMGet with ElementMultiFlagsFilter.
	* [UNSTABLE] See the below issues
	   - CacheManager stops by reconnect timeout after ZK sesssion timeout.

2017-03-24 [version 1.9.8] UNSTABLE
	* [Fix] Add bad command log message
	* [Fix] Add local cache hit debug log message
	* [UNSTABLE] See the below issues
	   - CacheManager stops by reconnect timeout after ZK sesssion timeout.

2017-02-27 [version 1.9.7] UNSTABLE
	* [Fix] Fix bopGetBulk reverse scan bug.
	* [Feature] Deprecate repl setting methods of cfb.
	   - Replication cloud is internally determined by checking
	     ZK directories for the given service code.
	   - The service code must be unique in each ZK ensemble.
	* [UNSTABLE] See the below issues
	   - CacheManager stops by reconnect timeout after ZK sesssion timeout.

2016-12-09 [version 1.9.6] UNSTABLE
	* [Fix] Fix bopGetBulk deserialization bug.
	* [UNSTABLE] See the below issues
	   - CacheManager stops by reconnect timeout after ZK sesssion timeout.

2016-08-31 [version 1.9.5] stable
	* [Fix] Add overflowAction availability check logic to collection APIs.
	* [Fix] Add overflowAction / readable options to collection store APIs.
	* [Fix] Remove unnecessary log messages.
	* [Fix] Refactor unit tests.
	* [Doc] Fix wrong comments about dropIfEmpty options in ArcusClientIf.
	* [Other] Update maven surefire plugin version to 2.19.
	* [Other] Apply CI tool (Travis-CI).

2016-07-08 [version 1.9.4] stable (but, verbose messages)
	* [Feature] bop incr/decr with initial value.
	* [Feature] CopyOnRead / CopyOnWrite to ARCUS front cache.
	* [Feature] Support replication.
	  - It can co-work with replication enabled cache cluster.
	* [Fix] Several minor mistakes in using elementFlag.
	* [Fix] Added null key checking logic to aysncSetBulk.
	* [Fix] Added arguments check logic to BulkWorker and its subclasses.
	* [Other] Followings are modified to get additional arguments.
	   - CollectionDelete, CollectionExist, SetExit
	   - CollecitionGet and its subclasses
	* [Other] Extensive code refactoring

2016-02-04 [version 1.9.3] stable (but, verbose messages)
	* Add cancel message to detect the cancel cause.
	* More correct error handling in getting/creating the client_info znode.
	* Fix a bug in getting socket address after DNS reverse lookup.
	* Cancel all operations given on the memcached node that leave from cluster.
	* Calculate the length of key string after translate it to byte array.
	* Add immediate reconnect for OperationException (delay=0).
	* Apply SPY-162 patch that "Also respect nagle setting on reconnect".

2015-11-09 [version 1.9.2] stable
	* Fix a mistake in compareTo of SMGetElement and SMGetTrimKey.
	* Fix a bug in sort-merge logic when unique bkeys are requested.

2015-11-03 [version 1.9.1] unstable
	* Restore the old smget interface to ensure backward compatibility.
	  So, both(the old one and the new one added since 1.9.0) smget
	  intefaces are supported.

2015-10-26 [version 1.9.0] stable
	* Add API type on operation objects.
	* Fix some mistakes in handling command pipeline response.
	* Treat EXISTS response as failure when create a collection.
	* Fix bug in getting null element flag by hexadecimal. 
	* Return DUPLICATED_TRIMMED
	  if smget response has both DUPLICATED and TRIMMED.
	* New smget interface - refer to Changelog of arcus-memcached.
	  - Continue smget even if some bkeys of a key are trimmed in bkey range.
	    - Missed keys are returned with the cause.
		  (NOT_FOUND, UNREADABLE, OUT_OF_RANGE).
	    - Trimmed keys are returned with the last bkey before trim.
	  - Support unique smget that remove duplicate bkeys as a option.
	  - Internally enhanced sort-merge implementation.
	* Throw exception if duplicate keys exist in multiple keys operation.
	* Some minor bug fixes.

2015-07-31 [version 1.8.2] stable
	* Change ZK_CONNECT_TIMEOUT from 5 to SESSION_TIMEOUT seconds.
	* Decrease default operation timeout - 1000 => 700 ms.
	* Add OperationType in all operation classes.
	* Fix CASMutator expiration issue (SPY-69 patch)
	* Cancel all WRITING operations in setupResend()
	  if failure mode is cancel.
	* Do not reset continous timeout when operation is cancelled.
	* Add timeout ratio threshold
	* Internal code optimization and code refactoring.

2015-01-13 [version 1.8.1] stable
	* Throw AdminConnectTimeoutException
	  if connecting to arcus admin timed out.
	* Increase ZK_CONNECT_TIMEOUT (2000 => 5000 ms)

2014-12-30 [version 1.8.0] stable
	* Add asyncBopFindPositionWithGet API.
	* Optimize the performance in finding the memcached node for a key. 
	* Add "# of operations added to memcached node"
	  in operation timeout message.
	* Add arcus java user guide document.
	* Fix - parse bkey string with long type, instead of int type.

2014-05-15 
	* arcus-java-client 1.7.0 is opened. (Apache License 2.0)