Documentum Fulltext Indexing Internals – High Availability

January 20, 2011 at 4:03 pm | Posted in Architecture, Performance | 2 Comments
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The installation of FAST Search in high availability mode is pretty well covered in the Installation and Administration documentation (see Powerlink for the documentation). However the details of administration tasks for HA setups is not so good and it is easy to mess up an installation if you are not careful. It helps to have some understanding of the configuration objects involved.

When you install the basic FAST setup, assuming for the sake of simplicity that we are only indexing 1 repository, you will have a machine containing an Index Server and an Index Agent. The Index Agent is the component that communicates with the Content Server to retrieve content that needs to be indexed. The Index Agent passes indexable content to the Index Server; the Index Server actually builds and maintains the indexes and responds to search requests.

After running the Index Server installation and Index Agent configuration for a repository you have an Index Server and Index Agent installed and running on the indexing machine and 3 configuration objects in the repository. The 3 objects represent the Index, the Index Server and the Index Agent respectively and are related as shown in the diagram.

The 3 objects are created every time the index configuration program is run. In particular the following attributes are always set as follows:

Object Attribute Value
dm_fulltext_index index_name repository_ftindex_01
dm_fulltext_index is_standby 0
dm_ftindex_agent_config index_name repository_ftindex_01
dm_ftindex_agent_config queue_user dm_fulltext_index_user
dm_ftengine_config object_name FAST Fulltext Engine Configuration

In a high availailability configuration you have another machine with an installed Index Server and Index Agent configuration. There will also be another 3 objects that define the second Index Server/Agent configuration. So how does the installation of a secondary index work?

Before running the 2nd Index Server install/Index Agent configuration program you need to run the HAPreInstall script. The script has the following effect on the 3 existing configuration objects:

Now the Index Server install/Index Agent configuration can be run on the 2nd machine resulting in 3 new objects (the original 3 objects are shown as shaded objects). Note that the 3 new objects have exactly the same attributes as for a ‘Basic’ installation. The Index Agent configuration program seems to have no ‘knowledge’ of whether it is running Basic or HA setup, it simply creates the same objects each time. The HAPreInstall and HAPostInstall scripts have the ‘intelligence’ to adjust the various configuration objects.

Finally you need to run the HAPostInstall script which makes the following changes:

Click on the table below to see the key attributes on these objects and how they appear in Basic and HA modes:

Basic and HA Fulltext attributes

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