38 lines
2.3 KiB
Markdown
38 lines
2.3 KiB
Markdown
---
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layout: article
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title: Locking Mechanism
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description: Data Controller uses a locking mechanism to handle parallel updates to the same table by different users. This mechanism is also available to non-DC applications.
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og_image: https://docs.datacontroller.io/img/locking-mechanism.drawio.png
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---
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# Locking Mechanism
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In any multi-user application a locking mechanism is necessary to avoid conflicts when the same table is updated by two people or processes. In Data Controller this is handled using the `DCLIB.MPE_LOCKANYTABLE` table, specifically using the [mp_lockanytable](https://core.sasjs.io/mp__lockanytable_8sas.html) macro.
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This macro is invoked whenever a process requires an exclusive lock on a table - first to mark the table as locked, and again to mark it as unlocked. The logic flow is demonstrated below:
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Notice above the red box - this situation can occur in unusual circumstances (such as a system shutdown or OS error). If you are waiting more than a minute or two for a table to be unlocked, then it is advised to follow the process below.
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## Unlock Process
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Before proceeding with an unlock, the first step should be to understand why the process is locked. By opening the [MPE_LOCKANYTABLE](/tables/mpe_lockanytable/) table it will be possible to see which user performed the lock, and when. Simply filter the table where `LOCK_STATUS_CD='LOCKED'`.
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If an unlock is deemed necessary, simply open this table in the EDIT menu, and change the value of `LOCK_STATUS_CD` from `LOCKED` to `UNLOCKED`.
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## Scalability
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This locking mechanism does not scale well if the table remains in SAS dataset (.sas7bdat) form. If you are deploying Data Controller for usage beyond 10-20 users then you are advised to put the control tables (DC library) in a database.
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## Third Party Applications
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Third party SAS apps may also make use of this locking table. This is handled by simply:
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1. Ensuring the DC library is assigned in the Service
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2. Using the [mp_lockanytable](https://core.sasjs.io/mp__lockanytable_8sas.html) macro to perform the lock
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3. Using the [mp_lockanytable](https://core.sasjs.io/mp__lockanytable_8sas.html) macro to perform the unlock
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4. Performing appropriate error handling to ensure an unlock if there are any issues in the service
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