You can use Structured Query Language (SQL)
functions for direct access to an SQL database, instead of
accessing the database as a Device. Using direct database access
can provide greater flexibility. The SQL functions provide access
to SQL databases through any ODBC-compatible database driver, for
example MS Access, FoxPro, Paradox, etc.
The SQL library used inCitectSCADA has a number of limitation
and these are documented in our Knowledge Base (article Q4014).
This library was not designed to handle large scale SQL data
transactions. For large volumes of data it is recommended that
(CitectHistorian) be used.
If you intend to use the embedded SQL library
in CitectSCADA, consider
Use "Simple" model for a SQL
database to limit transaction information logging to transaction
Use the fixed size of transaction
log to restrict the log file growing.
Back up the database regularly to
keep the transaction log size under control. When SQL Server
finishes backing up a database or its transaction log, it
automatically truncates the inactive portion of the transaction
log. If the transaction log file is full, your database
transactions will cease.
Keep working tables as small as
possible. When CitectSCADA
SQL adds or appends a new row to data table, it uses SELECT * first
to get column information. If there are hundred and thousand of
records in the table, this action will certainly hinder the
performance and may cause lock ups as these SQL Cicode functions
are block functions.
Use SQL Server trigger to remove
records from the working tables to the permanent tables. In this
way, sizes of the working tables that are directly interfaced with
Citect are not growing unrestricted.
Do NOT run SQL Cicode functions
on a critical CitectSCADA
machine. As SQL Cicode functions are block functions and running in
the main thread, #COM or trend miss samples are likely to occur
when SQL functions are executed on IO or trend. Similarly, an alarm
may miss a scan or a report may miss a trigger if the functions are
running on an alarm or report server.