Lock-free Backups

However, ALTER DATABASE and SNAPSHOT commands will not run while there is a backup job active on the relevant database. There is no difference between lock-free backup and the original locking backup with respect to the cluster operations lock. The backup takes the cluster operations lock for the entirety of the backup.

Lock-free backups are enabled when the lockfree_backup engine variable is set to ON and the disable_update_delete_distributed_transactions engine variable is set to OFF. The default values of lockfree_backup and disable_update_delete_distributed_transactions are ON and OFF, respectively.

Note

Lock-free backups cannot be made using BACKUP DATABASE ... WITH SPLIT PARTITIONS ....

Locking that Occurs if Lock-free Backups are Disabled

If lock-free backups are disabled and BACKUP DATABASE is run, the following applies before the backup starts:

The aggregator briefly blocks new queries from running across the cluster.
If there is a long-running write query executing, BACKUP DATABASE waits for the query to complete.

Once BACKUP DATABASE is running, queries against the cluster can proceed normally.

Commands Blocked by the BACKUP Process

ALTER DATABASE
DROP DATABASE
SNAPSHOT DATABASE

Commands Not Blocked by the BACKUP Process

CREATE TABLE (columnstore and rowstore)
ALTER TABLE (columnstore and rowstore)
DROP TABLE (columnstore and rowstore)
DELETE TABLE
INSERT TABLE
TRUNCATE TABLE (columnstore and rowstore)
CREATE INDEX
DROP INDEX (columnstore and rowstore)
CREATE VIEW
DROP VIEW
ANALYZE TABLE (columnstore and rowstore)
OPTIMIZE COLUMNSTORE TABLE
SHOW TABLE STATUS
SHOW DATABASE STATUS
OPTIMIZE ROWSTORE TABLE

Lock-free Backups

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Locking that Occurs if Lock-free Backups are Disabled

Commands Blocked by the BACKUP Process

Commands Not Blocked by the BACKUP Process

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