Package me.ahoo.cosid.jdbc

Class JdbcMachineLeaseStore

java.lang.Object

me.ahoo.cosid.jdbc.JdbcMachineLeaseStore

All Implemented Interfaces:

MachineLeaseStore

public class JdbcMachineLeaseStore
extends Object
implements MachineLeaseStore

MachineLeaseStore on the cosid_machine table, with conditional updates on (instance_id, last_timestamp) as the compare-and-set.

It uses the same rows as the 3.4 machine id distributor (a released machine id has an empty instance_id), so instances running either one, and 3.4 instances, can share a namespace during an upgrade. The lease keeps its renewal time, watermark and version in the renew_time, watermark and lease_version columns, and last_timestamp holds a value that is at least all of them and strictly increases, which 3.4 reads as its last timestamp and which is the lease version. lease_version equals last_timestamp when this store wrote the row last; otherwise a 3.4 instance did, and last_timestamp stands for the renewal time and the watermark. A 3.4 instance can write back the same last_timestamp (a host clock behind it), so handing a machine id to someone else never relies on the lease columns alone: expiry is judged on last_timestamp, exactly as 3.4 judges it, and a new owner starts after it. The table needs the stable column (ADD_STABLE_COLUMN_SQL) and the lease columns (ADD_LEASE_COLUMNS_SQL, PostgreSqlDialect.ADD_LEASE_COLUMNS_SQL): the constructor fails naming the statement when they are missing. The server clock is read with serverTimeSql: MYSQL_SERVER_TIME_SQL by default, PostgreSqlDialect.SERVER_TIME_SQL for PostgreSQL. Every statement has the query timeout, and writes are committed when the connection is not in auto-commit mode.

Since:

3.4.0

Field Summary

Fields

Modifier and Type	Field	Description
static final String	ADD_LEASE_COLUMNS_SQL	Migration of a cosid_machine table created before 4.0 (MySQL syntax).
static final String	ADD_STABLE_COLUMN_SQL	Migration of a table created before the stable column existed (MySQL syntax).
static final String	MYSQL_SERVER_TIME_SQL	Current time of a MySQL server in milliseconds.

Constructor Summary

Constructors

Constructor	Description
JdbcMachineLeaseStore(DataSource dataSource)
JdbcMachineLeaseStore(DataSource dataSource, Duration queryTimeout, String serverTimeSql)	Create a JDBC lease store.

Method Summary

Modifier and Type	Method	Description
Optional<Lease>	claimExpired(String namespace, InstanceId instanceId, int maxMachineId, long expiredBefore, long now)	Take over a machine id whose owner has not renewed it since expiredBefore.
Optional<Lease>	claimNew(String namespace, InstanceId instanceId, int maxMachineId, long now)	Take the next machine id that was never used in the namespace.
Optional<Lease>	claimReleased(String namespace, InstanceId instanceId, int maxMachineId, long now)	Take a machine id that a non-stable instance released on shutdown.
Optional<Lease>	claimSelf(String namespace, InstanceId instanceId, long now)	Take back the lease this instance already holds, renewing it to now, whether or not it has expired.
boolean	release(Lease lease, long watermark)	Release a lease on shutdown, if it is still the current version.
Optional<Lease>	renew(Lease lease, long now)	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).
long	serverTime()	The database server's clock, read with serverTimeSql.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

MYSQL_SERVER_TIME_SQL

public static final String MYSQL_SERVER_TIME_SQL

Current time of a MySQL server in milliseconds.

unix_timestamp() without an argument does not go through the session time zone: unix_timestamp(now(3)) does, and returns a time one hour too low during the repeated hour at the end of daylight saving time.

See Also:

• Constant Field Values

ADD_STABLE_COLUMN_SQL

public static final String ADD_STABLE_COLUMN_SQL

Migration of a table created before the stable column existed (MySQL syntax).

See Also:

• Constant Field Values

ADD_LEASE_COLUMNS_SQL

public static final String ADD_LEASE_COLUMNS_SQL

Migration of a cosid_machine table created before 4.0 (MySQL syntax).

See Also:

• Constant Field Values

Constructor Details

JdbcMachineLeaseStore

public JdbcMachineLeaseStore(DataSource dataSource)

JdbcMachineLeaseStore

public JdbcMachineLeaseStore(DataSource dataSource,
 Duration queryTimeout,
 String serverTimeSql)

Create a JDBC lease store.

Parameters:

queryTimeout - timeout applied to each statement, null or zero means no timeout

serverTimeSql - a query returning the database server's current time in milliseconds

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 database server's clock, read with serverTimeSql.

Specified by:

serverTime in interface MachineLeaseStore