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How Unions work

Learn about how Unions work in Index Manager Enterprise and how you can make best use of them.

What unions are for 

If you are running Index Manager Enterprise, you have the possibility to configure Unions. Unions offer the possibility for users to search and access files from several different indexed archives through a single entry point. The indexes connected in a union can either be local or on another Index Manager server in the network.

Unions can also be used to provide a backup index server in the event of server failure or if the primary server is down for maintenance reasons. The server that controls the union will then shift all search requests to the backup server until the main server comes back on line again. In total there are three ways to utilize backup servers in a union:

  1. To take over automatically in case the primary union member fails.
  2. To maximize performance when many clients search a primary union member.
  3. To reduce the load on the main union member by having the union server distribute search requests evenly between the main and the backup union member. (Also known as Round Robin search distribution.)

Other benefits of using a union

Unions offer the possibility to combine indexes from one or more Index Managers without having to reindex the archives (perform “double indexing”) several times. If, for instance, you have two indexed archives, you don’t have to create a whole new index to combine these two. Instead, they can be combined in a union to appear as a single index. The client’s user experience is the same and you are free to combine archives the way you see fit to create a large collection comprising several archives.

Things to consider when setting up a union

Unions provide a convenient way to combine several smaller archives into a larger one, and this functionality will often be utilized on a single Index Manager Enterprise server. However, when it comes to setting up unions to provide backup search servers, there are a few things to consider:

As explained above, unions can be used to configure backup indexes that take over in the event that the primary index is down, for instance if the server has been taken offline for maintenance or experiences a malfunction. In this case, if the Index Manager server that controls the unions is the same as the one that hosts the primary union members, taking down this server will cause the entire search functionality to fail, since there is no longer an active union server to distribute client searches. Hence, in environments where search availability is critical it makes sense to configure a separate union server that communicates with a primary and a backup server on the network - that is, three Index Manager servers in total. The Index Manager servers that host the primary and backup indexes do not have to be Enterprise versions, but naturally the Union server must be. (Unions are only available in Index Manager Enterprise.) You will naturally also have to consider availability solutions for your file servers.

Unions and FotoWeb

When Index Manager serves FotoWeb, it must push its metadata to the MongoDB instance controlled by FotoWeb. In a union comprising several Index Manager servers, all servers must be configured to push data to that database instance. All Index Manager servers must be the exact same version and build number.

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