Features and Improvements in ArangoDB 3.9

The following list shows in detail which features have been added or improved in ArangoDB 3.9. ArangoDB 3.9 also contains several bug fixes that are not listed here.

(Disjoint) SmartGraphs using SatelliteCollections (Enterprise Edition)

SmartGraphs have been extended with a new option to create SmartGraphs using SatelliteCollections. These SmartGraphs are capable of using SatelliteCollections within their graph definition and therefore can make use of all the benefits of SatelliteCollections.

Edge definitions can now be created between SmartCollections and SatelliteCollections. As SatelliteCollections are globally replicated to each participating DB-Server, regular graph traversals, weighted traversals, shortest path, and k shortest paths queries can partially be executed locally on each DB-Server. This means that query execution can be fully local whenever actual data from the SatelliteCollections is being processed. This can improve data locality and reduce the number of network hops between cluster nodes.

In case you do have collections that are needed in almost every traversal but are small enough to be copied over to every participating DB-Server, SmartGraphs with SatelliteCollections are the perfect fit, as this will increase the amount of local query execution.

SmartGraphs using SatelliteCollections can also be disjoint. A Disjoint SmartGraph prohibits edges connecting different SmartGraph components. The same rule applies to Disjoint SmartGraphs using SatelliteCollections. If your graph does not need edges between vertices with different SmartGraph attribute values, then you should enable this option. This topology restriction allows the query optimizer to improve traversal execution times, because the execution can be pushed down to a single DB-Server in many cases.

SmartGraphs using SatelliteCollections are only available in the Enterprise Edition.

ArangoSearch

Segmentation and Collation Analyzers

The new segmentation Analyzer type allows you to tokenize text in a language-agnostic manner as per Unicode Standard Annex #29, making it suitable for mixed language strings. It can optionally preserve all non-whitespace or all characters instead of keeping alphanumeric characters only, as well as apply case conversion.

The collation Analyzer converts the input into a set of language-specific tokens. This makes comparisons follow the rules of the respective language, most notable in range queries against Views.

See:

• segmentation Analyzer
• collation Analyzer

Analyzer locale normalization

Analyzers with a locale property no longer require that you specify the UTF-8 encoding (.utf-8) that ArangoDB uses for strings.

The syntax for specifying the language, and possibly a country, variant, keywords, is now the same as described in the ICU Documentation. The new collation Analyzer is currently the only Analyzer that supports all four: language[_COUNTRY][_VARIANT][@keywords] (square bracket denote optional parts). The text and norm Analyzers support language[_COUNTRY], the stem Analyzer only language.

The former syntax is still supported but automatically normalized to the new syntax.

ArangoSearch column cache (Enterprise Edition)

Views of the type arangosearch support new caching options.

Introduced in: v3.9.5

• You can enable the new cache option for individual View links or fields to always cache field normalization values in memory. This can improve the performance of scoring and ranking queries.

• You can enable the new cache option in the definition of a storedValues View property to always cache stored values in memory. This can improve the query performance if stored values are involved.

Introduced in: v3.9.6

• You can enable the new primarySortCache View property to always cache the primary sort columns in memory. This can improve the performance of queries that utilize the primary sort order.

• You can enable the new primaryKeyCache View property to always cache the primary key column in memory. This can improve the performance of queries that return many documents.

The cache size can be controlled with the new --arangosearch.columns-cache-limit startup option and monitored via the new arangodb_search_columns_cache_size metric.

ArangoSearch caching is only available in the Enterprise Edition.

See Optimizing View query performance for examples.

UI

Rebalance Shards for all databases in Web UI

The rebalance shards section displays a button for rebalancing shards. In previous versions, this button only appeared for the _system database, but now it appears in user-created databases as well if the user has the write permission for the database.

There is also a new startup option to limit the Maximum number of move shards.

Analyzers in Web Interface

A new menu item ANALYZERS has been added to the side navigation bar of the Web UI. Through this page, you can view existing Analyzers as well create new Analyzers. The UI is full-featured and lets you feed in all parameters and options that you could otherwise input through the HTTP or JavaScript API.

It also lets you copy configuration from an existing Analyzer, allowing for a much quicker workflow when your new Analyzer is very similar to an existing one.

It offers two edit/view modes - a form mode where a standard web form is used to capture user input, and a JSON mode where experienced users can directly write the raw Analyzer configuration in JSON format.

Additional Fields in Views Creation Form

ArangoSearch Views have 6 immutable fields (apart from name and type) that can only be set once at the time of creation. The web interface now includes these fields in the View creation form, so that you can set them when creating Views through the UI:

• primarySort
• primarySortCompression
• storedValues
• writebufferIdle
• writebufferActive
• writebufferSizeMax

Web interface session handling

The previously inactive startup parameter --server.session-timeout was revived and now controls the timeout for web interface sessions (and other sessions that are based on JWTs created by the /_open/auth API).

For security reasons, the default timeout value for web interface sessions has been reduced to one hour, after which a session is ended automatically. Web interface sessions that are active (i.e. that have any user activity) are automatically extended until the user ends the session explicitly or if there is a period of one hour without any user activity.

The timeout value for web interface sessions can be adjusted via the --server.session-timeout startup parameter (in seconds).

Configurable root redirect

Added two options to arangod to allow HTTP redirection customization for root (/) call of the HTTP API:

• --http.permanently-redirect-root: if true (default), use a permanent redirection (use HTTP 301 code), if false fall back to temporary redirection (use HTTP 302 code).

• --http.redirect-root-to: redirect of root URL to a specified path. Redirects to /_admin/aardvark/index.html if not set (default).

These options are useful to override the built-in web interface with some user-defined action.

AQL

Upsert with Index Hint

Added support for the indexHint and forceIndexHint options to the UPSERT operation. It will be used as a hint for the document lookup that is performed as part of the UPSERT operation, and can help in cases such as UPSERT not picking the best index automatically.

UPSERT { a: 1234 }
  INSERT { a: 1234, name: "AB"}
  UPDATE {name: "ABC"} IN myCollection
  OPTIONS { indexHint: "index_name", forceIndexHint: true }

See UPSERT Options

Decay Functions

Added three decay functions to AQL:

• DECAY_EXP()
• DECAY_LINEAR()
• DECAY_GAUSS()

Decay functions calculate a score with a function that decays depending on the distance of a numeric value from a user given origin.

DECAY_GAUSS(41, 40, 5, 5, 0.5) // 1
DECAY_LINEAR(5, 0, 10, 0, 0.2) // 0.6
DECAY_EXP(2, 0, 10, 0, 0.2)    // 0.7247796636776955

Vector Functions

Added three vector functions to AQL for calculating the cosine similarity (COSINE_SIMILARITY), Manhattan distance (named L1_DISTANCE), and Euclidean distance (named L2_DISTANCE):

• COSINE_SIMILARITY()
• L1_DISTANCE()
• L2_DISTANCE()

COSINE_SIMILARITY([0,1], [1,0]) // 0
L1_DISTANCE([-1,-1], [2,2]) // 6
L2_DISTANCE([1,1], [5,2]) // 4.1231056256176606

Traversal filtering optimizations

A post-filter on the vertex and/or edge result of a traversal will now be applied during the traversal to avoid generating the full output for AQL. This will have a positive impact on performance when filtering on the vertex/edge but still returning the path.

Previously all paths were produced even for non-matching vertices/edges. The new optimization now will check on the vertex/edge filter condition first and only produce the remaining paths.

For example, the query

FOR v, e, p IN 10 OUTBOUND @start GRAPH "myGraph"
  FILTER v.isRelevant == true
  RETURN p

can now be optimized, and the traversal statement will only produce paths for which the last vertex satisfies isRelevant == true.

This optimization is now part of the existing optimize-traversals rule and you will see the conditions under Filter / Prune Conditions in the query explain output (FILTER (v.`isRelevant` == true) in this example):

Execution plan:
 Id   NodeType          Est.   Comment
  1   SingletonNode        1   * ROOT
  2   TraversalNode        1     - FOR v  /* vertex */, p  /* paths: vertices, edges */ IN 10..10  /* min..maxPathDepth */ OUTBOUND 'A' /* startnode */  GRAPH 'myGraph'
  3   CalculationNode      1       - LET #5 = (v.`isRelevant` == true)   /* simple expression */
  4   FilterNode           1       - FILTER #5
  5   ReturnNode           1       - RETURN p

Indexes used:
 By   Name   Type   Collection   Unique   Sparse   Selectivity   Fields        Ranges
  2   edge   edge   edge         false    false       100.00 %   [ `_from` ]   base OUTBOUND

Traversals on graphs:
 Id  Depth   Vertex collections  Edge collections  Options                                  Filter / Prune Conditions      
 2   10..10  vert                edge              uniqueVertices: none, uniqueEdges: path  FILTER (v.`isRelevant` == true)

Optimization rules applied:
 Id   RuleName
  1   optimize-traversals

Traversal partial path buildup

There is now a performance optimization for traversals in which the path is returned, but only a specific sub-attribute of the path is used later (e.g. vertices, edges, or weight sub-attribute).

For example, the query

FOR v, e, p IN 1..3 OUTBOUND @start GRAPH "myGraph"
  RETURN p.vertices

only requires the buildup of the vertices sub-attribute of the path result p but not the buildup of the edges sub-attribute. The optimization can be observed in the query explain output:

Execution plan:
 Id   NodeType          Est.   Comment
  1   SingletonNode        1   * ROOT
  2   TraversalNode        1     - FOR v  /* vertex */, p  /* paths: vertices */ IN 1..3  /* min..maxPathDepth */ OUTBOUND 'A' /* startnode */  GRAPH 'myGraph'
  3   CalculationNode      1       - LET #5 = p.`vertices`   /* attribute expression */
  4   ReturnNode           1       - RETURN #5

Indexes used:
 By   Name   Type   Collection   Unique   Sparse   Selectivity   Fields        Ranges
  2   edge   edge   edge         false    false       100.00 %   [ `_from` ]   base OUTBOUND

Traversals on graphs:
 Id  Depth  Vertex collections  Edge collections  Options                                  Filter / Prune Conditions
 2   1..3   vert                edge              uniqueVertices: none, uniqueEdges: path                           

Optimization rules applied:
 Id   RuleName
  1   optimize-traversals
  2   remove-redundant-path-var

The remove-redundant-path-var optimization rule is applied and the TraversalNode’s comment indicates that only the vertices sub-attribute is built up for this query: p /* paths: vertices */

This optimization should have a positive impact on performance for larger traversal result sets.

Prune Variable

Added an option to store the PRUNE expression as a variable. Now, the PRUNE condition can be stored in a variable and be used later in the query without having to repeat the PRUNE condition:

FOR v, e, p IN 10 OUTBOUND @start GRAPH "myGraph"
  PRUNE pruneCondition = v.isRelevant == true
  FILTER pruneCondition
  RETURN p

The v.isRelevant == true condition is stored in the pruneCondition variable and used as a condition for FILTER later.

See Pruning.

Warnings on invalid OPTIONS

Invalid use of OPTIONS in AQL queries will now raise a warning when the query is parsed. This is useful to detect misspelled attribute names in OPTIONS, e.g.

INSERT ... INTO collection
  OPTIONS { overwrightMode: 'ignore' } /* should have been 'overwriteMode' */

It is also useful to detect the usage of valid OPTIONS attribute names that are used at a wrong position in the query, e.g.

FOR doc IN collection
  FILTER doc.value == 1234
  INSERT doc INTO other
    OPTIONS { indexHint: 'myIndex' } /* should have been used above for FOR */

In case options are used incorrectly, a warning with code 1575 will be raised during query parsing or optimization. By default, warnings are reported but do not lead to the query being aborted. This can be toggled by the startup option --query.fail-on-warnings or the per-query runtime option failOnWarnings.

Memory usage tracking

The AQL operations K_SHORTEST_PATHS and SHORTEST_PATH are now included in the memory usage tracking performed by AQL, so that memory acquired by these operations will be accounted for and checked against the configured memory limit (options --query.memory-limit and --query.memory-limit-global).

Execution of complex queries

Very large queries (in terms of query execution plan complexity) are now split into multiple segments which are executed using separate stacks. This prevents a potential stack overflow. To configure the number of execution nodes after such a stack splitting is performed, use the --query.max-nodes-per-callstack startup option. The default value is 200 for macOS, and 250 for the other supported platforms. The value can be adjusted per query via the maxNodesPerCallstack query option. Please note that the default values should work and adjusting the option is only useful for testing and debugging.

Query complexity limits

AQL now has some hard-coded query complexity limits, to prevent large programmatically generated queries from causing trouble (too deep recursion, enormous memory usage, long query optimization and distribution passes etc.).

The following limits have been introduced:

• a recursion limit for AQL query expressions. An expression can now be up to 500 levels deep. An example expression is 1 + 2 + 3 + 4, which is 3 levels deep 1 + (2 + (3 + 4)). The expression recursion is limited to 500 levels.
• a limit for the number of execution nodes in the initial query execution plan. The number of execution nodes in the initial query execution plan is limited to 4000. This number includes all execution nodes of the initial execution plan, even if some of them could be optimized away later by the query optimizer during plan optimization.

AQL queries that violate these limits will fail to run, and instead abort with error 1524 (“too much nesting or too many objects”) during setup.

disableIndex hint

Introduced in: v3.9.1

In some rare cases, an AQL query can be executed faster if it ignores indexes. You can force the optimizer not use an index for any given FOR loop by setting the new disableIndex hint to true:

FOR doc IN collection OPTIONS { disableIndex: true }
  FILTER doc.value <= 99
  RETURN doc.other

See the FOR Operation Options for details.

maxProjections hint

Introduced in: v3.9.1

If an AQL query accesses 5 or fewer attributes of a collection in a FOR loop, the query optimizer changes the strategy for retrieving the data from the storage engine. Instead of extracting full documents, only subsets of the documents are fetched.

Such projections are typically faster as long as there are not too many of them but it depends on the number of attributes and their size. The new maxProjections hint lets you adjust the threshold to fine-tune your queries.

FOR doc IN collection OPTIONS { maxProjections: 7 }
  RETURN [ doc.val1, doc.val2, doc.val3, doc.val4, doc.val5, doc.val6, doc.val7 ]

See the FOR Operation Options for details.

RocksDB block cache control

The new query option fillBlockCache can be used to control the population of the RocksDB block cache with data read by the query. The default value for this per-query option is true, which means that any data read by the query will be inserted into the RocksDB block cache if not already present in there. This mimics the previous behavior and is a sensible default.

Setting the option to false allows to not store any data read by the query in the RocksDB block cache. This is useful for queries that read a lot of (cold) data which would lead to the eviction of the hot data from the block cache.

AQL function to return a shard ID for a document

A new AQL function is available which allows you to obtain the responsible shard for any document in a collection by specifying its shard keys.

Improved query explanation for index scans

Introduced in: v3.9.3

The AQL query explainer now displays index scan + document lookup comments for queries that use an index for filtering, but need to fetch more document data from the storage engine.

 FOR doc IN coll
   FILTER doc.attr == 42 // indexed attribute
   RETURN doc

Execution plan:
 Id   NodeType        Est.   Comment
  1   SingletonNode      1   * ROOT
  6   IndexNode          1     - FOR doc IN coll   /* persistent index scan, index scan + document lookup */    
  5   ReturnNode         1       - RETURN doc

Previously, it was labeled as index scan only, obfuscating the fact that there are document lookups needed. Covering index queries are still labeled index scan, index only as before.

Number of cluster requests in profiling output

Introduced in: v3.9.5

The query profiling output in the web interface and arangosh now shows the number of HTTP Requests for queries that you run against cluster deployments in the Query Statistics:

Query String (33 chars, cacheable: false):
 FOR doc IN coll
   RETURN doc._key

Execution plan:
 Id   NodeType          Site  Calls   Items   Filtered   Runtime [s]   Comment
  1   SingletonNode     DBS       3       3          0       0.00024   * ROOT
  9   IndexNode         DBS       3       0          0       0.00060     - FOR doc IN coll   /* primary index scan, index only (projections: `_key`), 3 shard(s) */    
  3   CalculationNode   DBS       3       0          0       0.00025       - LET #1 = doc.`_key`   /* attribute expression */   /* collections used: doc : coll */
  7   RemoteNode        COOR      6       0          0       0.00227       - REMOTE
  8   GatherNode        COOR      2       0          0       0.00209       - GATHER   /* parallel, unsorted */
  4   ReturnNode        COOR      2       0          0       0.00008       - RETURN #1

Indexes used:
 By   Name      Type      Collection   Unique   Sparse   Cache   Selectivity   Fields       Stored values   Ranges
  9   primary   primary   coll         true     false    false      100.00 %   [ `_key` ]   [  ]            *

Optimization rules applied:
 Id   RuleName
  1   scatter-in-cluster
  2   distribute-filtercalc-to-cluster
  3   remove-unnecessary-remote-scatter
  4   reduce-extraction-to-projection
  5   parallelize-gather

Query Statistics:
 Writes Exec   Writes Ign   Scan Full   Scan Index   Cache Hits/Misses   Filtered   Requests   Peak Mem [b]   Exec Time [s]
           0            0           0            0               0 / 0          0          9          32768         0.00564

Edge cache refilling (experimental)

Introduced in: v3.9.6

A new feature to automatically refill the in-memory edge cache is available. When edges are added, modified, or removed, these changes are tracked and a background thread tries to update the edge cache accordingly if the feature is enabled, by adding new, updating existing, or deleting and refilling cache entries.

You can enable it for individual INSERT, UPDATE, REPLACE, and REMOVE operations in AQL queries (using OPTIONS { refillIndexCaches: true }), for individual document API requests that insert, update, replace, or remove single or multiple edge documents (by setting refillIndexCaches=true as query parameter), as well as enable it by default using the new --rocksdb.auto-refill-index-caches-on-modify startup option.

The new --rocksdb.auto-refill-index-caches-queue-capacity startup option restricts how many edge cache entries the background thread can queue at most. This limits the memory usage for the case of the background thread being slower than other operations that invalidate edge cache entries.

The background refilling is done on a best-effort basis and not guaranteed to succeed, for example, if there is no memory available for the cache subsystem, or during cache grow/shrink operations. A background thread is used so that foreground write operations are not slowed down by a lot. It may still cause additional I/O activity to look up data from the storage engine to repopulate the cache.

In addition to refilling the edge cache, the cache can also automatically be seeded on server startup. Use the new --rocksdb.auto-fill-index-caches-on-startup startup option to enable this feature. It may cause additional CPU and I/O load. You can limit how many index filling operations can execute concurrently with the --rocksdb.max-concurrent-index-fill-tasks option. The lower this number, the lower the impact of the cache filling, but the longer it takes to complete.

The following metrics are available:

This feature is experimental.

Also see:

• AQL INSERT operation
• AQL UPDATE operation
• AQL REPLACE operation
• AQL REMOVE operation
• Document HTTP API
• Edge cache refill options

Multi-dimensional Indexes (experimental)

ArangoDB 3.9 features a new index type zkd. It can be created like other indexes on collections. In contrast to the persistent index type (same for hash and skiplist, which today are just aliases for persistent), it lifts the following restriction.

A persistent index can only be used with query filters where a conjunction of equalities on a prefix of indexed fields covers the filter. For example, given a collection with a persistent index on the fields ["a", "b"]. Then the following filters can be satisfied by the index:

• FILTER doc.a == @a
• FILTER doc.a == @a && doc.b == @b
• FILTER doc.a == @a && @bl <= doc.b && doc.b <= @bu

While the following filters cannot, or only partially, be satisfied by a persistent index:

• FILTER doc.b == @b
• FILTER @bl <= doc.b && doc.b <= @bu
• FILTER @al <= doc.a && doc.a <= @au && @bl <= doc.b && doc.b <= @bu

A zkd index can be used to satisfy them all. An example where this is useful are documents with an assigned time interval, where a query should find all documents that contain a given time point, or overlap with some time interval.

There are also drawbacks in comparison with persistent indexes. For one, the zkd index is not sorted. Secondly, it has a significantly higher overhead, and the emerging performance is much more dependent on the distribution of the dataset, making it less predictable. A third limitation is that zkd indexes can only be created for index values which are IEEE 754 doubles.

Multi-dimensional Indexes are an experimental feature.

Server options

Maximum number of move shards

The --cluster.max-number-of-move-shards startup option limits the maximum number of move shards operations that can be made when the Rebalance Shards button is clicked in the Web UI. For backwards compatibility purposes, the default value is 10. If the value is 0, then the tab containing this button will be inactive and the button cannot be clicked.

Extended naming convention for databases

There is a new startup option --database.extended-names-databases to allow database names to contain most UTF-8 characters. This feature is experimental in ArangoDB 3.9, but will become the norm in a future version.

Running the server with the option enabled provides support for database names that are not comprised within the ASCII table, such as Japanese or Arabic letters, emojis, letters with accentuation. Also, many ASCII characters that were formerly banned in the traditional naming convention are now accepted.

Example database names that can be used with the new naming convention: "España", "😀", "犬", "كلب", "@abc123", "København", "München", "Россия", "abc? <> 123!"

The ArangoDB client tools arangobench, arangodump, arangoexport, arangoimport, arangorestore, and arangosh ship with full support for the extended database naming convention.

Note that the default value for --database.extended-names-databases is false for compatibility with existing client drivers and applications that only support ASCII names according to the traditional database naming convention used in previous ArangoDB versions. Enabling the feature may lead to incompatibilities up to the ArangoDB instance becoming inaccessible for such drivers and client applications.

Please be aware that dumps containing extended database names cannot be restored into older versions that only support the traditional naming convention. In a cluster setup, it is required to use the same database naming convention for all Coordinators and DB-Servers of the cluster. Otherwise the startup will be refused. In DC2DC setups it is also required to use the same database naming convention for both datacenters to avoid incompatibilities.

Also see Database names.

ICU Language

Introduced in: v3.9.1

A new server startup option for setting the language was added. The new --icu-language option will replace the existing --default-language option, and only one of the two can be set.

Also see ArangoDB Server General Options.

Logging

The server now has two flags for retaining or escaping control and Unicode characters in the log. The flag --log.escape is now deprecated and, instead, the new flags --log.escape-control-chars and --log.escape-unicode-chars should be used.

• --log.escape-control-chars:

  This flag applies to the control characters, that have hex codes below \x20, and also the character DEL with hex code \x7f.

  When the flag value is set to false, control characters will be retained when they have a visible representation, and replaced with a space character in case they do not have a visible representation. For example, the control character \n is visible, so a \n will be displayed in the log. Contrary, the control character BEL is not visible, so a space will be displayed instead.

  When the flag value is set to true, the hex code for the character is displayed, for example, the BEL character will be displayed as its hex code, \x07.

  The default value for this flag is true to ensure compatibility with previous versions.

• --log.escape-unicode-chars:

  If its value is set to false, Unicode characters will be retained and written to the log as-is. For example, 犬 will be logged as 犬. If the flag value is set to true, any Unicode characters are escaped, and the hex codes for all Unicode characters are logged instead. For example, 犬 would be logged as its hex code, \u72AC.

  The default value for this flag is set to false for compatibility with previous versions.

Also see Logging.

Version information

The arangod server now provides a command --version-json to print version information in JSON format. This output can be used by tools that need to programmatically inspect an arangod executable.

A pseudo log topic "all" was added. Setting the log level for the “all” log topic will adjust the log level for all existing log topics. For example, --log.level all=debug will set all log topics to log level “debug”.

Cluster option for shard synchronization timeout

Introduced in: v3.9.2

A --cluster.shard-synchronization-attempt-timeout startup option has been added, letting you limit the amount of time to spend in shard synchronization attempts (in seconds).

The default timeout value is 20 minutes. Running into the timeout does not lead to a synchronization failure, but continues the synchronization shortly after. Setting a timeout can help to split the synchronization of large shards into smaller chunks and release snapshots and archived WAL files on the leader earlier.

This change also introduces a new arangodb_sync_timeouts_total metric that counts the number of timed-out shard synchronization attempts.

RocksDB range delete operations in cluster

Introduced in: v3.9.3

The new --rocksdb.use-range-delete-in-wal startup option controls whether the collection truncate operation in a cluster can use RangeDelete operations in RocksDB. Using RangeDeletes is fast and reduces the algorithmic complexity of the truncate operation to O(1), compared to O(n) when this option is turned off (with n being the number of documents in the collection/shard).

Previous versions of ArangoDB used RangeDeletes only on a single server, but never in a cluster.

The default value for this startup option is true, and the option should only be changed in case of emergency. This option is only honored in the cluster. Single server and Active Failover deployments use RangeDeletes regardless of the value of this option.

Note that it is not guaranteed that all truncate operations use a RangeDelete operation. For collections containing a low number of documents, the O(n) truncate method may still be used.

RocksDB periodic compaction TTL

Introduced in: v3.9.3

A --rocksdb.periodic-compaction-ttl startup option has been added to control the time-to-live (in seconds) for periodic compaction of .sst files in RocksDB, based on the .sst file age.

The default value from RocksDB is ~30 days. You can set the option to 0 to avoid periodic auto-compaction.

Option for file copying method on Linux

Introduced in: v3.9.4

A Linux-specific --use-splice-syscall startup option has been added to control whether the Linux-specific splice() syscall should be used for copying file contents. Set it to false to use a less efficient, but more portable user-space file copying method, which should work on all file systems.

See ArangoDB Server Options for details.

AQL query logging

Introduced in: v3.9.5

There are three new startup options to configure how AQL queries are logged:

• --query.log-failed for logging all failed AQL queries, to be used during development or to catch unexpected failed queries in production (off by default)
• --query.log-memory-usage-threshold to define a peak memory threshold from which on a warning is logged for AQL queries that exceed it (default: 4 GB)
• --query.max-artifact-log-length for controlling the length of logged query strings and bind parameter values. Both are truncated to 4096 bytes by default.

ArangoSearch column cache limit

Introduced in: v3.9.5

The new --arangosearch.columns-cache-limit startup option lets you control how much memory (in bytes) the ArangoSearch column cache is allowed to use.

Cluster supervision options

Introduced in: v3.9.6

The following new options allow you to delay supervision actions for a configurable amount of time. This is desirable in case DB-Servers are restarted or fail and come back quickly because it gives the cluster a chance to get in sync and fully resilient without deploying additional shard replicas and thus without causing any data imbalance:

• --agency.supervision-delay-add-follower: The delay in supervision, before an AddFollower job is executed (in seconds).

• --agency.supervision-delay-failed-follower: The delay in supervision, before a FailedFollower job is executed (in seconds).

Edge cache refill options

Introduced in: v3.9.6

• --rocksdb.auto-refill-index-caches-on-modify: Whether to automatically (re-)fill in-memory edge cache entries on insert/update/replace operations by default. Default: false.
• --rocksdb.auto-refill-index-caches-queue-capacity: How many changes can be queued at most for automatically refilling the edge cache. Default: 131072.
• --rocksdb.auto-fill-index-caches-on-startup: Whether to automatically fill the in-memory edge cache with entries on server startup. Default: false.
• --rocksdb.max-concurrent-index-fill-tasks: The maximum number of index fill tasks that can run concurrently on server startup. Default: the number of cores divided by 8, but at least 1.

Introduced in: v3.9.10

• --rocksdb.auto-refill-index-caches-on-followers: Control whether automatic refilling of in-memory caches should happen on followers or only leaders. The default value is true, i.e. refilling happens on followers, too.

Agency option to control whether a failed leader adds a shard follower

Introduced in: v3.9.7

A --agency.supervision-failed-leader-adds-follower startup option has been added with a default of true (behavior as before). If you set this option to false, a FailedLeader job does not automatically configure a new shard follower, thereby preventing unnecessary network traffic, CPU load, and I/O load for the case that the server comes back quickly. If the server has permanently failed, an AddFollower job is created anyway eventually.

RocksDB auto-flushing

Introduced in: v3.9.10

A new feature for automatically flushing RocksDB Write-Ahead Log (WAL) files and in-memory column family data has been added.

An auto-flush occurs if the number of live WAL files exceeds a certain threshold. This ensures that WAL files are moved to the archive when there are a lot of live WAL files present, for example, after a restart. In this case, RocksDB does not count any previously existing WAL files when calculating the size of WAL files and comparing its max_total_wal_size. Auto-flushing fixes this problem, but may prevent WAL files from being moved to the archive quickly.

You can configure the feature via the following new startup options:

• --rocksdb.auto-flush-min-live-wal-files: The minimum number of live WAL files that triggers an auto-flush. Defaults to 10.
• --rocksdb.auto-flush-check-interval: The interval (in seconds) in which auto-flushes are executed. Defaults to 3600. Note that an auto-flush is only executed if the number of live WAL files exceeds the configured threshold and the last auto-flush is longer ago than the configured auto-flush check interval. This avoids too frequent auto-flushes.

Overload control

Starting with version 3.9.0, ArangoDB returns an x-arango-queue-time-seconds HTTP header with all responses. This header contains the most recent request queueing/dequeuing time (in seconds) as tracked by the server’s scheduler. This value can be used by client applications and drivers to detect server overload and react on it.

The arangod startup option --http.return-queue-time-header can be set to false to suppress these headers in responses sent by arangod.

In a cluster, the value returned in the x-arango-queue-time-seconds header is the most recent queueing/dequeuing request time of the Coordinator the request was sent to, except if the request is forwarded by the Coordinator to another Coordinator. In that case, the value will indicate the current queueing/dequeuing time of the forwarded-to Coordinator.

In addition, client applications and drivers can optionally augment the requests they send to arangod with the header x-arango-queue-time-seconds. If set, the value of the header should contain the maximum server-side queuing time (in seconds) that the client application is willing to accept. If the header is set in an incoming request, arangod will compare the current dequeuing time from its scheduler with the maximum queue time value contained in the request header. If the current queueing time exceeds the value set in the header, arangod will reject the request and return HTTP 412 (precondition failed) with the error code 21004 (queue time violated). In a cluster, the x-arango-queue-time-seconds request header will be checked on the receiving Coordinator, before any request forwarding.

Support info API

A new HTTP REST API endpoint GET /_admin/support-info was added for retrieving deployment information for support purposes. The endpoint returns data about the ArangoDB version used, the host (operating system, server ID, CPU and storage capacity, current utilization, a few metrics) and the other servers in the deployment (in case of active failover or cluster deployments).

As this API may reveal sensitive data about the deployment, it can only be accessed from inside the _system database. In addition, there is a policy control startup option --server.support-info-api that controls if and to whom the API is made available. This option can have the following values:

• disabled: support info API is disabled.
• jwt: support info API can only be accessed via superuser JWT.
• hardened (default): if --server.harden is set, the support info API can only be accessed via superuser JWT. Otherwise it can be accessed by admin users only.
• public: everyone with access to the _system database can access the support info API.

License Management (Enterprise Edition)

The Enterprise Edition of ArangoDB requires a license to activate it. ArangoDB 3.9 comes with a new license management that lets you test ArangoDB for three hours before requiring a license key to keep the Enterprise Edition features activated.

There is a new JavaScript API for querying the license status and to set a license key (typically run in arangosh):

db._getLicense();
db._setLicense("<license-string>");

There are two new REST API routes to do the same, GET /_admin/license and PUT /_admin/license.

See License Management and the License Management HTTP API. Miscellaneous changes ---------------------

Collection statuses

The previously existing collection statuses “new born”, “loading”, “unloading” and “unloaded” were removed, as they weren’t actively used in arangod.

These statuses were last relevant with the MMFiles storage engine, when it was important to differentiate which collections were present in main memory and which weren’t. With the RocksDB storage engine, all that is automatically handled anyway, and the mentioned statuses are not important anymore.

The “Load” and “Unload” buttons for collections have also been removed from the web interface. This change also obsoletes the load() and unload() calls for collections as well as their HTTP API equivalents. The APIs will remain in place for now for downwards-compatibility but have been changed to no-ops. They will eventually be removed in a future version of ArangoDB.

Cluster-internal timeouts

The internal timeouts for inactive cluster transactions on DB-Servers was increased from 3 to 5 minutes.

Previously transactions on DB-Servers could expire quickly, which led to spurious “query ID not found” or “transaction ID not found” errors on DB servers for multi-server queries/transactions with unbalanced access patterns for the different participating DB-Servers.

Transaction timeouts on Coordinators remain unchanged, so any queries/transactions that are abandoned will be aborted there, which will also be propagated to DB-Servers.

Deployment mode “leader-follower” no longer supported

The Leader/Follower deployment mode in which two single servers were set up as a leader and follower pair (without any kind of automatic failover) was deprecated and removed from the documentation.

Recommended alternatives are the Active Failover deployment option and the OneShard feature in a cluster.

Traffic accounting metrics

Introduced in: v3.8.9, v3.9.6

The following metrics for traffic accounting were added:

I/O heartbeat

Introduced in: v3.8.7, v3.9.2

An I/O heartbeat has been added which checks that the underlying volume is writable with reasonable performance. The test is done every 15 seconds and can be switched off.

Use the accompanying new metrics to check for test failures:

These metrics are only populated if the new --database.io-heartbeat startup option is set to true (which is the default).

Lock stripes option for RocksDB transactions

Introduced in: v3.9.2

The new --rocksdb.transaction-lock-stripes option controls the number of lock stripes to use for RocksDB’s transaction lock manager. Higher values can be used to reduce a potential contention in the lock manager.

The option defaults to the number of available cores, but is increased to a value of 16 if the number of cores is lower.

Configurable CACHE_OBLIVIOUS option for jemalloc

Introduced in: v3.9.7

The jemalloc memory allocator supports an option to toggle cache-oblivious large allocation alignment. It is enabled by default, but disabling it helps to save 4096 bytes of memory for every allocation which is at least 16384 bytes large. This is particularly beneficial for the RocksDB buffer cache.

You can now configure the option by setting a CACHE_OBLIVIOUS environment variable to the string true or false before starting ArangoDB.

See ArangoDB Server environment variables for details.

WAL file tracking metrics

Introduced in: v3.9.10

The following metrics for write-ahead log (WAL) file tracking have been added:

Client tools

Increased default number of threads

The default value for the --threads startup parameter was changed from 2 to the maximum of 2 and the number of available CPU cores for the following client tools:

• arangodump
• arangoimport
• arangorestore

The --threads option works dynamically, its value depends on the number of available CPU cores. If the amount of available CPU cores is less than 3, a threads value of 2 is used. Otherwise the value of threads is set to the number of available CPU cores.

This change can help to improve performance of imports, dumps or restore processes on machines with multiple cores in case the --threads parameter was not previously used. As a trade-off, the change may lead to an increased load on servers, so any scripted imports, dumps or restore processes that want to keep the server load under control should set the number of client threads explicitly when invoking any of the above client tools.

arangoimport

arangoimport received a new startup option --merge-attributes that allows you to create additional attributes in CSV/TSV imports based on other attribute values and hard-coded string literals/separators.

The following example would add a new attribute named fullName that consists of the values of the firstName and lastName columns, separated by a colon character :, as well as as an additional attribute nameAndId that builds on the new fullName attribute and concatenates it with a hyphen - and the value of the id column:

arangoimport \
  --merge-attributes fullName=[firstName]:[lastName] \
  --merge-attributes nameAndId=[fullName]-[id] \
  ...

Also see Merging Attributes.

arangoimport also provides a new --datatype startup option, in order to fix the datatypes for certain attributes in CSV/TSV imports. For example, in the the following CSV input file, it is unclear if the numeric values should be imported as numbers or as stringified numbers for the individual attributes:

key,price,weight,fk
123456,200,5,585852
864924,120,10,9998242
9949,70,11.5,499494
6939926,2130,5,96962612

To determine the datatypes for the individual columns, arangoimport can be invoked with the --datatype startup option, once for each attribute:

--datatype key=string
--datatype price=number
--datatype weight=number
--datatype fk=string

This will turn the numeric-looking values in the key attribute into strings but treat the attributes price and weight as numbers. Finally, the values in attribute fk will be treated as strings again.

See Overriding data types per attribute.

arangobench

Histogram is now switched off by default (the --histogram.generate flag set to false). To display it, set the flag to true. If this option is disabled, but other histogram flags are addressed, e.g. --histogram.interval-size 500, everything will still run normally, but a warning message will be displayed saying that the histogram is switched off and using that flag has no effect.

arangobench now prints a short description of the test case started, so it is easier to figure out what operations are carried out by a test case. Several test cases in arangobench have been deprecated because they do not target real world use cases but were rather writing for some internal testing. The deprecated test cases will be removed in a future version to clear up the list of test cases.

arangobench now supports multiple Coordinators. The flag --server.endpoint can be specified multiple times, as in the example below:

arangobench \
  --server.endpoint tcp://[::1]::8529 \
  --server.endpoint tcp://[::1]::8530 \
  --server.endpoint tcp://[::1]::8531 \
  ...

This does not compromise the use of the other client tools, that preserve the behavior of having one Coordinator and one endpoint.

Also see arangobench Options

arangodump

arangodump now supports multiple Coordinators. The flag --server.endpoint can be used multiple times, as in the example below:

arangodump \
  --server.endpoint tcp://[::1]::8529 \
  --server.endpoint tcp://[::1]::8530 \
  --server.endpoint tcp://[::1]::8531 \
  ...

This does not compromise the use of the other client tools that preserve the behavior of having one Coordinator and one endpoint.

Also see arangodump examples

arangorestore

arangorestore now supports multiple Coordinators. The flag --server.endpoint can be used multiple times, as in the example below:

arangorestore \
  --server.endpoint tcp://[::1]::8529 \
  --server.endpoint tcp://[::1]::8530 \
  --server.endpoint tcp://[::1]::8531 \
  ...

This does not compromise the use of the other client tools that preserve the behavior of having one Coordinator and one endpoint.

Introduced in: v3.8.7, v3.9.2

A new --enable-revision-trees option has been added to arangorestore, which adds the syncByRevision and usesRevisionsAsDocumentIds attributes to the collection structure if they are missing. As a consequence, these collections created by arangorestore are able to use revision trees and a faster getting-in-sync procedure after a restart.

The option defaults to true, meaning that the attributes are added if they are missing. If you set the option to false, the attributes are not added to the collection structure. If the attributes are already present in the dump data, they are not modified by arangorestore, irrespective of the setting of this option.

Also see arangorestore examples.

arangovpack

The arangovpack utility supports more input and output formats (JSON and VelocyPack, plain or hex-encoded). The former options --json and --pretty have been removed and have been replaced with separate options for specifying the input and output types:

• --input-type (json, json-hex, vpack, vpack-hex)
• --output-type (json, json-pretty, vpack, vpack-hex)

The former option --print-non-json has been replaced with the new option --fail-on-non-json which makes arangovpack fail when trying to emit non-JSON types to JSON output.

Internal changes

The compiler version used to build the ArangoDB Linux executables has been upgraded from g++ 9.3.0 to g++ 10.2.1. g++ 10 is also the expected version of g++ when compiling ArangoDB from source.

The bundled version of the Snappy compression library has been upgraded from version 1.1.8 to version 1.1.9.

The bundled version of the RocksDB library has been upgraded from 6.8 to 6.27.

For ArangoDB 3.9, the bundled version of rclone is 1.51.0.

The minimum architecture requirements have been raised from the Westmere architecture to the Sandy Bridge architecture. 256-bit AVX instructions are now expected to be present on all targets that run ArangoDB 3.9 executables. If a target does not support AVX instructions, it may fail with SIGILL at runtime.