Shard
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Defined in: src/cluster/sharding/Shard.ts:63
One shard of a sharded type — child of its ShardRegion, parent of the
entities whose id hashes into it. Its entire job is the entity
lifecycle: spawn, watch, stop, and buffer traffic for an entity that is
on its way out.
Routing, buffering and coordinator bookkeeping stay in the region; the
policy decisions about when to passivate stay there too (the region sees
every message on this node, a single shard only sees its own slice). The
shard just executes PassivateEntity. Keeping it that thin is what
lets maxEntities go on meaning “per node” rather than silently becoming
“per shard”.
Being a real actor is the point: a shard now has a path
(/system/cluster/sharding/region-<type>/shard-<n>), so it is addressable
from anywhere in
the cluster, it shows up in the actor tree, and handoff is simply “stop the
shard” — the runtime terminates the entities underneath and only then
reports back.
Extends
Section titled “Extends”Actor<ShardInbox>
Constructors
Section titled “Constructors”Constructor
Section titled “Constructor”new Shard(
config):Shard
Defined in: src/cluster/sharding/Shard.ts:79
Parameters
Section titled “Parameters”config
Section titled “config”Returns
Section titled “Returns”Shard
Overrides
Section titled “Overrides”Properties
Section titled “Properties”config
Section titled “config”
readonlyconfig:ShardConfig
Defined in: src/cluster/sharding/Shard.ts:79
Accessors
Section titled “Accessors”entityCount
Section titled “entityCount”Get Signature
Section titled “Get Signature”get entityCount():
number
Defined in: src/cluster/sharding/Shard.ts:99
Number of live entities — the region mirrors this for its stats replies.
Returns
Section titled “Returns”number
Methods
Section titled “Methods”displayName()
Section titled “displayName()”displayName():
string
Defined in: src/Actor.ts:192
Human-readable name for this actor in log lines and in the DevTools actor tree (#891). Defaults to the full path — which is already the log source, so an actor that doesn’t override this logs exactly as it did before.
override displayName(): string { return `User(${this.entityId})`; }Purely cosmetic. The path stays the identity everywhere that routes,
correlates or aggregates — metric labels, tracing attributes, dead
letters, ActorRef.toString(), every wire identifier — so a display
name is free to be ambiguous, unstable, or shared between actors.
Resolved on every record, not captured once. Two consequences:
keep it cheap and side-effect free, and expect it to be called before
preStart (hence the optional chain — the context is attached after
construction). In exchange a name may be derived from state, and it
updates when that state does. Throwing, or returning anything but a
non-empty string, falls back to the path and warns once: a naming
hook must not be able to take a log line down with it.
ActorOptions.withDisplayName(...) outranks this, for the same reason
withSupervisorStrategy(...) outranks supervisorStrategy
— the spawn site is the more specific statement. It has to: every
Behaviors actor is a TypedActor that inherits this default, so a
method that won would silently swallow the spawn-site value for exactly
the actors that have no subclass to override. For a name that only
becomes known at runtime, this.context.setDisplayName(...) outranks
both.
Returns
Section titled “Returns”string
Inherited from
Section titled “Inherited from”onReceive()
Section titled “onReceive()”onReceive(
message):void
Defined in: src/cluster/sharding/Shard.ts:86
Arm order is deliberate: every message to an entity lands here, and the
two instanceOf checks are the expensive ones — putting the envelope
first keeps the hot path a single string comparison.
Parameters
Section titled “Parameters”message
Section titled “message”ShardInbox
Returns
Section titled “Returns”void
Overrides
Section titled “Overrides”postRestart()
Section titled “postRestart()”postRestart(
_reason):void|Promise<void>
Defined in: src/Actor.ts:152
Called on the fresh instance after a restart. Default: call preStart().
Parameters
Section titled “Parameters”_reason
Section titled “_reason”Error
Returns
Section titled “Returns”void | Promise<void>
Inherited from
Section titled “Inherited from”postStop()
Section titled “postStop()”postStop():
void|Promise<void>
Defined in: src/Actor.ts:103
Called after the actor has been terminated. Children are already stopped.
Returns
Section titled “Returns”void | Promise<void>
Inherited from
Section titled “Inherited from”preRestart()
Section titled “preRestart()”preRestart(
_reason,_message?):void|Promise<void>
Defined in: src/Actor.ts:119
Called before a restart, on the instance about to be thrown away.
The default calls postStop() and nothing else.
Override to release what the instance holds outside itself — a file handle, an open socket, a broker connection — or to do something other than drop the message that failed.
Stopping this actor’s children is not done here: the framework tears
them down after this hook returns and waits for them before building the
replacement, because postRestart re-runs preStart and a named child
needs its name back. To keep the children instead, see
Actor.stopChildrenOnRestart.
Parameters
Section titled “Parameters”_reason
Section titled “_reason”Error
_message?
Section titled “_message?”ShardInbox
Returns
Section titled “Returns”void | Promise<void>
Inherited from
Section titled “Inherited from”preStart()
Section titled “preStart()”preStart():
void|Promise<void>
Defined in: src/Actor.ts:100
Called after construction and before the first message is processed.
Returns
Section titled “Returns”void | Promise<void>
Inherited from
Section titled “Inherited from”stopChildrenOnRestart()
Section titled “stopChildrenOnRestart()”stopChildrenOnRestart():
boolean
Defined in: src/Actor.ts:149
Whether a restart tears this actor’s children down before rebuilding it.
Default: true.
A restart replaces the Actor instance while the cell — and therefore
the child map — survives. Keeping the children was the old behaviour and
it made an ordinary pattern impossible: postRestart re-runs preStart,
so an actor that spawns a named child there hit Child name … is not unique on its first restart and never recovered (#634).
Override to false when the children are expensive to rebuild, hold
state the parent cannot restore, or are supervised independently — a
connection pool, say. They then outlive the restart exactly as before,
and it is on you to make preStart idempotent — by adopting the survivor
from the cell, this.child = this.context.child('name').toNullable() ?? this.context.spawn(Child, 'name'), or with context.spawnAnonymous.
An instance field cannot do it: preStart runs on a fresh instance
after every restart, so this.child ??= … is always unset and re-spawns
into the name the surviving child still holds, which fails the spawn and
restarts the actor again.
This is a separate hook rather than a preRestart override because the
teardown has to be awaited: the new instance cannot be built until the
old children are actually gone, and preRestart has no way to tell the
cell that it started something worth waiting for.
Returns
Section titled “Returns”boolean
Inherited from
Section titled “Inherited from”supervisorStrategy()
Section titled “supervisorStrategy()”supervisorStrategy():
SupervisorStrategy
Defined in: src/Actor.ts:160
Supervisor strategy for this actor’s children. Defaults to restart, up to 10 times per minute, then stop.