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[KB488]Changing the HDS tables

Tags: HDS

Historical data
15 years ago
By RM
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Applies to:

PcVue version 8.10 onwards.
Summary:

This article explains how a manual modification of the tables created by the HDS can cause certain errors and in particular memory leaks.
Solution:

The problem arises from the structure of HDS tables. If these are modified outside of PcVue, the behavior of the PcVue application can change completely. We strongly advise against making changes to those structures.

  1. Examples of potential problems
    1. If primary keys are deleted from the log and trend tables, doubloons (duplicate entries) may occur. That is because without primary key control, PcVue and the HDS cannot handle instances of doubloons. So there is a high risk of the HDS or PcVue crashing at any time.
    2. If the indexes created by PcVue have been partially changed to adapt them for a client application using those tables, the PcVue’s performance in reading/writing can be severely affected. You must then reconstruct the original indexes to restore adequate performance.
    3. If an extra column has been added to a table’s structure, for example to facilitate data extraction by a third-party tool, this can in some cases cause memory leaks.
      So it is vital not to change the structure of the HDS tables.
  2. Corrections to apply & potential work-arounds
    1. Close PcVue, delete the existing tables and restart PcVue to recreate a standard table structure. The data for the client application should have been saved previously so as to be re-imported to the database.
    2. If an extra column is required for the client application, it is essential that that application uses a SQL View (to be created) that encapsulates the Log and Trend tables plus the extra column.

Created on: 02 Sep 2011 Last update: 13 May 2024