Package me.ahoo.cosid.mongo

Class MongoMachineLeaseStore

java.lang.Object
me.ahoo.cosid.mongo.MongoMachineLeaseStore
All Implemented Interfaces:
MachineLeaseStore
public class MongoMachineLeaseStore extends Object implements MachineLeaseStore
MachineLeaseStore on the cosid_machine collection: every claim, renewal and release is one atomic findOneAndUpdate or conditional update.

It uses the same documents as the 3.4 machine id distributor (a released machine id has an empty instanceId), so instances running either one can share a namespace during an upgrade. The server clock is the localTime of the hello command, and every operation has the driver's client-side timeout (timeoutMS). Claims use pipeline updates, which need MongoDB 4.2 or later. On a sharded cluster the server clock is the mongos one, so keep the mongos clocks in sync.

Documents keep the 3.4 fields. The last timestamp stays the expiry check and the version, as in 3.4; it never decreases and is at least every renewal and watermark, so a claim starts after it. A lease still carries its own watermark and renewal time: renewing leaves the watermark alone and reports the store time it renewed at, while the document is written with a last timestamp that covers both. Do not add fields for them: the last timestamp already covers both, since expiry and takeover are anchored on it, and the ZooKeeper store keeps the same model.

Since:
3.4.0

  • Constructor Details

    • MongoMachineLeaseStore

      public MongoMachineLeaseStore(com.mongodb.client.MongoDatabase database, Duration timeout)
      Create a MongoDB lease store.
      Parameters:
      timeout - client-side timeout of each operation, must be positive: the lease adapter holds a lock during each call

  • Method Details

    • claimSelf

      public Optional<Lease> claimSelf(String namespace, InstanceId instanceId, long now)
      Description copied from interface: MachineLeaseStore
      Take back the lease this instance already holds, renewing it to now, whether or not it has expired. The watermark is raised to at least now and the stored renewed at.
      Specified by:
      claimSelf in interface MachineLeaseStore
      Returns:
      the renewed lease, or empty if the instance holds none (it was released or recycled)

    • claimReleased

      public Optional<Lease> claimReleased(String namespace, InstanceId instanceId, int maxMachineId, long now)
      Description copied from interface: MachineLeaseStore
      Take a machine id that a non-stable instance released on shutdown.
      Specified by:
      claimReleased in interface MachineLeaseStore
      maxMachineId - the largest machine id allowed: released ids above it (left over from a larger machine bit) are never returned
      Returns:
      the new lease, or empty if no released machine id up to maxMachineId is left

    • claimExpired

      public Optional<Lease> claimExpired(String namespace, InstanceId instanceId, int maxMachineId, long expiredBefore, long now)
      Description copied from interface: MachineLeaseStore
      Take over a machine id whose owner has not renewed it since expiredBefore. Leases of stable instances are never taken over.
      Specified by:
      claimExpired in interface MachineLeaseStore
      maxMachineId - the largest machine id allowed: expired ids above it are never returned
      expiredBefore - leases renewed at or before this time are expired
      Returns:
      the new lease, or empty if no lease up to maxMachineId has expired

    • claimNew

      public Optional<Lease> claimNew(String namespace, InstanceId instanceId, int maxMachineId, long now)
      Description copied from interface: MachineLeaseStore
      Take the next machine id that was never used in the namespace.
      Specified by:
      claimNew in interface MachineLeaseStore
      maxMachineId - the largest machine id allowed
      Returns:
      the new lease, or empty if every machine id up to maxMachineId is in use

    • renew

      public Optional<Lease> renew(Lease lease, long now)
      Description copied from interface: MachineLeaseStore
      Renew a lease to now if it is still the current version, even when now is before the stored renewed at (the store clock moved back). The watermark is unchanged.
      Specified by:
      renew in interface MachineLeaseStore
      Returns:
      the renewed lease, or empty if the lease was taken over, released or changed since

    • release

      public boolean release(Lease lease, long watermark)
      Description copied from interface: MachineLeaseStore
      Release a lease on shutdown, if it is still the current version. A stable instance keeps its machine id (only the watermark is updated); otherwise the machine id becomes available to MachineLeaseStore.claimReleased(java.lang.String, me.ahoo.cosid.machine.InstanceId, int, long).
      Specified by:
      release in interface MachineLeaseStore
      watermark - the generator's last timestamp: the watermark becomes at least this, so that the next owner waits if its clock is behind
      Returns:
      false if the lease was taken over or changed since

    • serverTime

      public long serverTime()
      The localTime of the server's hello command, or of isMaster on servers before 4.2.10, which have no hello.
      Specified by:
      serverTime in interface MachineLeaseStore