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===GUI===
Database locking is currently disabled if the BaseX GUI is used.
==Process Locking==
In order to enable locking on global (process) level, the option <code>[[Options#GLOBALLOCK|GLOBALLOCK]]</code> can be set to {{Code|true}}. This can e.g. be done by editing your {{Code|.basex}} file (see [[Options]] for more details). If process locking is active, a process that performs write operations will queue all other operations.
[[Category:Server]]
[[Category:Internals]]
→Concurrency Control
* Subsequent operations (read or write) will be queued until the updating transaction has completed.
Each database has its own queue: An update on database A will not block operations on database B. This is under the premise that it can be statically determined, i.e., before the transaction is evaluated) , which databases will be accessed by a transaction (see [[#Limitations|below]]). The number of maximum parallel transactions can be adjusted with the [[Options#PARALLEL|PARALLEL]] option. With {{Version|8.6}}, locking has been improved: * Jobs without database access will never be locked. Globally locking jobs can now be executed in parallel with non-locking jobs.* A {{Option|FAIRLOCK}} option has been added: By default, read transactions will now be favored, and transactions that access no databases can be evaluated even if the transactions limit has been reached.
==External Side Effects==
You can consult the query info output (which you find in the [[GUI#Visualizations|Info View]] of the GUI or which you can turn on by setting <code>[[Options#QUERYINFO|QUERYINFO]]</code> to {{Code|true}}) to find out which databases have been locked by a query.
=File-System Locks=
==Database Locks==
To avoid database corruptions that are caused by accidental write operations from different JVMs, a shared lock is requested on the database table file ({{Code|tbl.basex}}) whenever a database is opened. If an update operation is triggered, and if no exclusive lock can be acquired, it will be rejected with the message "Database ... is currently opened by another process.".
Please note that you cannot 100% rely on this mechanism, as it is not possible to synchronize operations across different JVMs. You will be safe when using the client/server or HTTP architecture.
=Changelog=
;Version 8.6
* Updated: New {{Option|FAIRLOCK}} option, improved detection of lock patterns.
;Version 7.8
* Added: Locks can also be acquired on [[Java Bindings#Locking|Java functions]].
;Version 7.6
* Added: database locking introduced, replacing process locking.
;Version 7.2.1
* Updated: pin files replaced with shared/exclusive filesystem locking.
;Version 7.2
* Added: pin files to mark open databases.
;Version 7.1
* Added: update lock files.
