* allow to access last operation tick of the transaction
* modify IResearchLink to rely on last commtted tick
* get rid of writing arangosearch markers to WAL
* further implementation
* local changes in iresearch
* add recovery states
* properly handle link creation during recovery
* adjust test cases
* properly handle nested transactions
* ungreylist recovery tests
* add more recovery tests
* do not use transaction to pass recovery tick
* do not store recoveryTick in MMFilesRecoveryState
* adjust tests
* fix mmfiles
* cleanup
* add context validity check
* fix tests
* fix more tests
* ensure subscription is not being released during commit
* address review comment
* final cleanup
* fix crash
* fix tests
* address test failures
* address review comments
* address review comments
* properly set recovery tick even if no recovery happened
* issue 526.3: update analyzer feature to store analyzer definitions in per-vocbase system collections
* address merge issues
* address another merge issue
* issue 511.4: ensure IResearchLink can be initialized without view as required for db-server, minor code fixes and cleanup
* remove unnessesary checks
* revert last change due to test failures
* fix typo in change revert
* try to address random test failures
* issue 381.4.1: create a separate IResearchLink implementation for use with ClusterEngine
* backport: ensure StorageEngineMock assigns unique transaction ids
* delegate index normalization on the ClusterEngine to the 'actualEngine'
* add initial implementation of scatter view rule and node
* add tests for `IResearchViewNode` and `IResearchViewScatterNode`
* add missing check
* modify IResearch execution nodes to use references instead of pointers
* use view id in searialized `ExecutionNode` representation instead of the name
* add cluster mode stubs and checks
* very first attempt to distribute IResearchViewNode
* further implementation of cluster-wide arangosearch views
* fix invalid json format
* add tests for coordinator iresearch view
* allow to retrieve a list of existing views on a coordinator
* more tests for coordinator iresearch view
* some fixes to enable query explanation
* remove Collection dependency from RemoteNode
* remove unnecessary remote ArangoSearch view scatter
* fix explanation appearance
* add some assertions
* minor fixes
* implement IResearchViewCoordinator::updateProperties
* fix view DDL issues
* handle link modifications in DDL operations
* add coordinator implementation of iresearch view links
* fix tests
* further coordinator based view DDL implementation
* further IResearchViewCoordinator implementation
* add initial implementation of AgencyMock
* fix some tests
* code cleanup
* extend test + some fixes
* more tests for IResearchViewCoordinator
* fix tests for IResearchLinkCoordinator
* some fixes after merge
* fix tests
* remove declaration of nonexistent (previously removed) method
* some fixes after review
* remove string duplication
* more tests and fixes
* more fixes and tests
* more tests
* one more test
* fix 'use-after-free' asan error
* fix non-enterprise tests issues