LOCK BUCKETS

Description

Bucket-based lock.

Precautions

It can be called only during hash bucket scaling out.

LOCK BUCKETS is useless outside a transaction block: the lock would remain held only to the completion of the statement. If LOCK BUCKETS is out of any transaction block, an error is reported.

Syntax

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LOCK BUCKETS (bucketlist) IN {ACCESS SHARE|ACCESS EXCLUSIVE} MODE [CANCELABLE];

Parameters

Parameters of LOCK BUCKETS are as follows:

• bucketlist

  Specifies the list of buckets to be locked.

  Value range: For each bucket, the value range is [0,1023].

• ACCESS SHARE

  Allows only read operations on a bucket.

• ACCESS EXCLUSIVE

  Guarantees that the holder is the only transaction accessing the bucket in any way.

• CANCELABLE

  Allows the waiting thread to send CANCEL signals to the holding threads and waiting threads.

Examples

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gaussdb=# START TRANSACTION;

gaussdb=# LOCK BUCKETS (0,1,2,3) IN ACCESS EXCLUSIVE MODE;

gaussdb=# COMMIT;