Full Text Search Error: Exception of type 'System.OutOfMemoryException' was thrown. (4262235)

AfterMail.Default: System.OutOfMemoryException: Exception of type 'System.OutOfMemoryException' was thrown.
at Lucene.Net.Index.SegmentReader.Norm.Bytes()
at Lucene.Net.Index.SegmentReader.GetNorms(String field)
at Lucene.Net.Index.SegmentReader.Norms(String field)
at Lucene.Net.Search.TermQuery.TermWeight.Scorer(IndexReader reader, Boolean scoreDocsInOrder, Boolean topScorer)
at Lucene.Net.Search.IndexSearcher.Search(Weight weight, Filter filter, Collector collector)
at Lucene.Net.Search.IndexSearcher.Search(Weight weight, Filter filter, Int32 nDocs)
at Lucene.Net.Search.Searcher.Search(Query query, Filter filter, Int32 n)
at Lucene.Net.Search.Searcher.Search(Query query, Int32 n)
at AfterMail.BusinessLayer.AMIndexSearcherFactory.WarmupSearcher(AMIndexSearcher searcher)
at AfterMail.BusinessLayer.AMIndexSearcherFactory.Monitor()

With large Full Text Indexes (of over 100GB, for example) it is possible that an "Out of Memory" error will be logged when the Full Text Search Service attempts to reload a copy of the index into memory.

The initial loading of an index into memory when the service restarts works as expected and users are able to search, but then after approximately an hour the Full Text Search Service will attempt to reload the index into memory in order to make recently indexed data available in users searches.

1) Optimising the index does mitigate the problem but unfortunately does not resolve it in all cases.

2) Modify the duration at which the FTS reloads the index using the following Archive Manager Configuration Editor entry:

3) Create a batch file to restart the Full Text Search Service and schedule it to repeatedly run before the time specified in the value for the Full Text Searcher Cache Time Hours timer. For example, schedule the batch file to restart the FTS service once an hour if the value of Full Text Searcher Cache Time Hours is the default 1 hour.

4) Moving the Full Text Search Service to a dedicated 64-bit machine where more memory is available has resolved this issue for some customers. This would require Archive Manager v4.5 or higher.

Resolved on version 4.5