List of Route Handles

AllAsyncRoute

Immediately sends the same request to all child route handles. Does not wait for response. Returns the default reply for the request right away as returned by NullRoute.

Properties:

• children: list of child route handles.

AllFastestRoute

Immediately sends the same request to all child route handles. Returns the first non-error reply to come back, or if all replies are errors, then the last error reply. Other requests complete in the background and their replies are silently ignored.

Properties:

• children: list of child route handles.

AllInitialRoute

Immediately sends the same request to all child route handles. Waits for the reply from first route handle in the children list and returns it. Other requests are completed asynchronously in the background.

Properties:

• children: list of child route handles.

AllMajorityRoute

Immediately sends the same request to all child route handles. Waits for replies until a non-error result appears (half + 1) times (or all replies if that never happens), and then returns the latest reply that it sees (the effect is that typically the reply with the most common result is returned).

Properties:

• children: list of child route handles.

AllSyncRoute

Immediately sends the same request to all child route handles. Collects all replies and responds with the "worst" reply (i.e., the error reply, if any).

Properties:

• children: list of child route handles.

DevNullRoute

Same as NullRoute, but with mcrouter stats reporting. See Stats list.

ErrorRoute

Immediately returns the error reply for each request. You can specify the error value to return: "ErrorRoute|MyErrorValueHere"

FailoverRoute

Sends the request to the first child in the list and waits for the reply. If the reply is a non-error, returns it immediately. Otherwise, depending on the settings, sends the request to the second child, and so on. If all children respond with errors, returns the last error reply. Note: miss (key not found) doesn't count for an error. See MissFailoverRoute to failover misses.

Properties:

• children
  List of child route handles

• failover_errors (object or array, optional, default: all errors)
  This property allows specifying for which errors to failover. If this property is missing, we assume default behavior: failover on every error received, independent of the operation. The following example shows how to failover only on connect_timeout, timeout, connect_error and tko errors (for a full list of errors, refer to Errors List).

  [ "connect_timeout", "timeout", "connect_error", "tko" ]

  The above config is valid for every operation (get, set, delete, ...). It is possible to go further and tweak the failover behavior per operation type:

  {
    "gets": [ "connect_timeout", "timeout", "connect_error", "tko" ],
    "updates": [], // empty array: will not failover.
    // "deletes" is missing, default behavior (all errors) will be assumed.
  }

  To find out more about errors and operations, see Routing.

• failover_limit (object, optional, default: no limit)

  {
    "rate": double, /* 0.0 <= rate <= 1.0 */
    "burst": integer /* 1 <= burst <= 1000000000 */ 
  }

  We rate limit failover requests over normal requests using token bucket algorithm. Rate 0.5 means we'll failover at most 50% of all requests, doesn't matter how many requests we send per second. If we hit the limit, error received from first destination in children list be returned immediately.

FailoverWithExptimeRoute

FailoverRoute with additional settings. Sends request to normal route handle. If it responds with an error, checks settings and failovers to failover if necessary.

Properties:

• normal
  All requests sent here first.
• failover
  List of route handles to which to route in case of error reply from normal.
• failover_exptime (int, optional, default 60)
  TTL (in seconds) for update requests sent to failover. Useful when failing over "sets" to a special pool with a small TTL to protect against temporary outages.
• settings (deprecated, use failover_errors instead)
• failover_errors (object or array, optional, default: all errors)
  Same as in FailoverRoute. This option replaces settings, which is now deprecated.

HashRoute

Routes to the destination based on key hash.

Properties:

• children
  List of child route handles.
• salt (string, optional, default empty)
  Specifies salt to be added to key before hashing
• hash_func (string, optional, default Ch3)
  Which hashing function to use: Ch3, Crc32 or WeightedCh3. More about hash functions see here
• weights (list of doubles, valid only when hash_func is WeightedCh3)
  Weight for each destination. If weights has more elements than children, extra values are ignored. If weights has fewer elements than number of children, missing values are assumed to be 0.5.

HostIdRoute

Routes to one destination chosen based on client host ID.

Properties:

• children: list of child route handles.
• salt (string, optional): if present, mcrouter will use hash(salt, client host ID) instead of client host ID.

LatestRoute

Attempts to "behave well" in how many new targets it connects to. Creates a FailoverRoute with at-most failover_count child handles chosen pseudo-randomly based on client host ID.

Properties:

• children
  List of child route handles.
• failover_count (int, optional, default 5)
  Number of route handles to route to.
• failover_errors (object or array, optional, default: all errors)
  Same as described in FailoverRoute.
• salt (string, optional): if present, mcrouter will use hash(salt, client host ID) instead of client host ID.

LoadBalancerRoute

Load balances to a destination from a list of children. The two supported load balancing algorithms are “weighted-hashing” and “two-random-choices”.

In weighted-hashing, requests are hashed between the children taking into account a cached server load for each child.

In two-random-choices, two children are chosen at random and the child with the lowest load is selected.

In both algorithms, the load for each child is cached from a previous response and has a configurable expiry time. On expiry it will be reset to the configured default server load.

Properties:

• children List of child route handles.
• salt (string, optional, default empty) Specifies salt to be added to key before hashing
• load_ttl_ms (int, optional, default 100ms) Expiration time in ms before a childs cached server load will be reset to default_server_load_percent
• default_server_load_percent (int, optional, default 50) Default server load of each child
• failover_count (int, optional, default 1) Number of times to route the request. This is currently only supported in weighted-hashing.
• algorithm (string, optional, default weighted-hashing) Algorithm that will be used to load balance. Supports “weighted-hashing” and “two-random-choices”.

MigrateRoute

This route handle changes behavior based on Migration mode.

1. Before migration starts, sends all requests to from route handle.
2. Between start_time and (start_time + interval), sends all requests except deletes to from route handle, sends all delete requests to both from and to route handle. For delete requests, returns reply from worst of two replies (i.e., any error reply).
3. Between (start_time + interval) and (start_time + 2*interval), sends all requests except deletes to to route handle and sends all delete requests to both from and to route handle. For delete requests, returns reply from worst among two replies.
4. After (start_time + 2*interval), sends all requests to to route handle.

Properties:

• from
  Route handle that routes to destination from which we are migrating.
• to
  Route handle that routes to destination to which we are migrating.
• start_time (int)
  Time in seconds from epoch when migration starts.
• interval (int, options, default 3600)
  Duration of migration (in seconds)

MissFailoverRoute

For get-like requests, sends the same request sequentially to each route handle in the list, in order, until the first hit reply. If all replies result in errors/misses, returns the reply from the last destination in the list.

Properties:

• children: list of child route handles.
• return_best_on_error (optional, default is false): if true, returns the "best" reply if all replies are errors/misses (e.g. miss is better than error), instead of returning the reply from the last destination.

ModifyExptimeRoute

Modifies exptime (TTL) for all requests.

Properties:

• target: child route handle.
• exptime (int)
  New TTL (in seconds) for requests.
• action (optional, default is set) Valid options: set or min. If action is set, always uses new exptime. If action is min, uses new exptime only if it's lower than one specified in request.

NullRoute

Returns the default reply for each request right away. Default replies are:

• delete - not found
• get - not found
• set - not stored

No properties.

PrefixSelectorRoute

Sends to different targets based on specified key prefixes.

Properties:

• wildcard
  Default route handle if the key prefix does not match any other specified policies.

• policies
  Object, with operation name as key and route handle for specified operation as value. Example:

"route": {
       "type": "PrefixSelectorRoute",
       "policies": {
         "shr": "PoolRoute|shared_pool"
       },
       "wildcard": "PoolRoute|local_pool_in_second_cluster"
     }

See Prefix routing setup for a more detailed example.

Note: PrefixSelectorRoute can be only used as a topmost route handle in config tree. It's the only route handle with such restriction.

PoolRoute

Route handle that routes to a pool. With different settings, it provides the same functionality as HashRoute, but also allows rate limiting, shadowing, et cetera.

Properties:

• pool (string or object)
  If it is a string, routes to the pool with the specified name. If it is an object, creates a pool on the fly. This object has the same format as item of the pools property described earlier, but with additional name property. Example:

 {
   "type": "PoolRoute",
   "pool": {
     "name": "MyPool",
     "servers": [ /* pool hosts here */ ]
   }
 }

• shadows (optional, default empty)
  List of objects that define additional route handles to which mcrouter should duplicate routed data (shadow). Each object in shadows has following properties:

  • target
    Route handle for shadow requests.
  • index_range (array of two integers, both in [0, number of servers in pool - 1])
    Only requests sent to servers from index_range will be sent to target,
  • key_fraction_range (array of two doubles, both in [0, 1])
    Only requests with key hash from key_fraction_range will be sent to target. The hash used for this purpose is SpookyHashV2.

• hash (optional, default Ch3)
  String or object that defines hash function, same as in HashRoute.

• rates (optional, default no rate limiting)
  If set, enables rate limiting requests to prevent server overload. The object that defines rate and burst are parameters of a token bucket algorithm:

 {
   "type": "PoolRoute",
   "pool": "MyPool",
   "rates": {
     "gets_rate": double (optional)
     "gets_burst": double (optional)
     "sets_rate": double (optional)
     "sets_burst": double (optional)
     "deletes_rate": double (optional)
     "deletes_burst": double (optional)
   }
 }

• slow_warmup (optional, default empty)
  Enables slow warm up for this pool. If enabled, as soon the hit rate of a server in this pool drops bellow a certain threshold, a percentile of the requests will be sent to failoverTarget straight away.
  The slow warmup route has the following properties:
  • failoverTarget
    Route handle for requests when the server is cold.
  • settings (optional)
    Settings allow customization of slow warm up logic. It has the following properties:
    • enable_threshold (number between 0.0 and 1.0)
      Slow warm up will be enabled as soon as the hit rate of the server drops bellow this threshold.
    • disable_threshold (number between 0.0 and 1.0, must be greater than enable_threshold)
      Slow warm up will be disabled as soon as the hit rate of the server goes above this threshold.
    • start (optional, default 0.1, must be a number between 0.0 and 1.0)
      Fraction of requests to send to the server being warmed up when its hit rate is 0.
    • step (optional, default 1.0, must be a number between 0.0 and 100.0)
      Step by which the percentage of requests sent to the server should be incremented when its hit rate increases.
    • min_requests (optional, default 100)
      Minimum number of requests necessary to start calculating the hit rate. Before this number is reached, the server is considered warm.

OperationSelectorRoute (previously: PrefixPolicyRoute)

Sends to different targets based on specified operations.

Properties:

• default_policy
  Default route handle.
• operation_policies
  Object, with operation name as key and route handle for specified operation as value. Example:

 {
   "type": "OperationSelectorRoute",
   "default_policy": "PoolRoute|A",
   "operation_policies": {
     "delete": {
       "type": "AllSyncRoute",
       "children": [ "PoolRoute|A", "PoolRoute|B" ]
     }
   }
 }

Sends gets and sets to pool A, sends deletes to pool A and pool B. Valid operations are 'add', 'get', 'set', 'delete', 'incr', 'decr'. Route handles for operation_policies are parsed in alphabetical order (delete, get, set).

RandomRoute

Routes to one random destination from list of children.

Properties:

• children: list of child route handles.

WarmUpRoute

Allows for substantial changes to the number of boxes in a pool without increasing the miss rate and, consequently, to the load on the underlying storage or service.

All sets and deletes go to the target ("cold") route handle. Gets are attempted on the "cold" route handle and, in case of a miss, data is fetched from the "warm" route handle (where the request is likely to result in a cache hit). If "warm" returns a hit, the response is forwarded to the client and an asynchronous request, with the configured expiration time, updates the value in the "cold" route handle.

Properties:

• cold
  Route handle that routes to "cold" destination (with empty cache).
• warm
  Route handle that routes to "warm" destination (with filled cache).
• exptime (int, optional, in seconds)
  Expiration time for warm up requests.