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71 lines
3.0 KiB
Markdown
71 lines
3.0 KiB
Markdown
---
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layout: article
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title: CAS Tables
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description: Dealing with CAS (in-memory) Tables in Data Controller
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og_image: /img/SAS-Viya-and-CAS-300x249.png
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---
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!!! warning
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Work in Progress!
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# CAS Tables
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CAS Tables require special consideration in Data Controller with regards to the following topics:
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- System Account
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- Loading
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- Unloading
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- Special Variables
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## System Account
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Despite having a shared SYSUSERID, the SPRE session will (by default) authenticate using the logged-in user credentials. To get around this, it is necessary to set up the CAS connection in the autoexec - ie, before the user takes over the session. The code snippet will be:
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```sas
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%let _CASHOST_ = <your-host>;
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%let _CASPORT_ = 5570;
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cas dcsession authdomain="<your-domain>" sessopts=(caslib=casuser);
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```
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The credentials need to be first placed in the viya credentials service as described [here](https://go.documentation.sas.com/doc/en/pgmsascdc/v_073/casref/n0z3r80fjqpobvn1lvegno9gefni.htm#p11ynzjbz96oq1n17rgt2utv6swj).
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Another approach can be to use the `AUTHINFO="authentication-file" option, as described [here](https://go.documentation.sas.com/doc/en/pgmsascdc/v_073/casref/n0z3r80fjqpobvn1lvegno9gefni.htm#n174yddgn85756n1v5q4yb881xa0).
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Note that since the CAS connection is using a shared account, the CASUSER library is never shown in the DC interface.
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## Loading
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It can happen that a CAS table is configured in Data Controller but not loaded into memory. In this case, when a user selects the table, it will be automatically loaded.
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### REPLACE Load Type
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The REPLACE load type is fully supported on CAS tables. When a REPLACE load is applied to a CAS target, Data Controller:
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1. Casts any fixed-length character variables in the staging table to varchar (matching the target table structure), since fixed char variables cannot be appended to CAS varchar columns.
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2. Truncates the target CAS table in-place using `proc cas; table.deleteRows` (CAS tables do not support SQL deletes).
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3. Appends the staged data via a data step with `sessref=dcsession`.
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The truncate is deliberately the last step before the append, to minimise the time in which the target table is empty. See [MPE_TABLES](/dcc-tables/#loadtype) for general REPLACE documentation.
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## Unloading
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After an approval, the in-memory version of the CAS Table will be updated. To apply this to the underlying file on disk, the following code must be executed (eg in a POST APPROVE HOOK):
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```sas
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proc casutil;
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save casdata="mytable" incaslib="mycaslib"
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casout="mytable" outcaslib="mycaslib"
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replace;
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quit;
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```
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## Special Variables
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Processing of data in Data Controller is performed in SPRE with SAS datasets - and as such, it is not possible to process character variables longer than 32k or other CAS specific data types.
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## Temporary Table Cleanup
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Temporary `casuser` tables created during loading (eg the REPLACE cast-and-append step above) are cleaned up correctly, including in error conditions. If a load is aborted before completion, any temp tables created mid-process are dropped before the lock is released.
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