Chapter 15. Full text search 341
The maximum file size that can be processed is a function of the heap size. When you set the 
maximum heap size to a value greater than 2 GB, the file size limits for text, XML, and binary 
documents must be increased for new collections. For each 8.3 MB of heap memory over 
2 GB, the values of the file size limits (60 MB by default) must be increased by 1 MB (up to 
400 MB), as demonstrated by the following formula:
Max file size = 60 MB + (heap memory - 2 GB) / 8.3
For example, a 2 GB maximum heap size results in 60 MB as the maximum size of a file that 
can be processed.
15.3.6  Index considerations
The most significant sizing option for the FTS Server system is the hard disk requirements for 
the full text index. The FTS Server requires a fast disk subsystem. Because the textual 
representation of each indexed document is stored in the disk subsystem, a considerable 
amount of disk space might be needed.
Index size calculation
Although the disk space usage depends on the text in each document, this usage is linear to 
the original size of the indexed data. Typically, the size of the index on the disk is 50% - 150% 
of the original text size as illustrated in the following formulas:
minimum disk space = Number of documents x document size x 50% 
maximum disk space required = Number of documents x document size x 150%
The actual percentage, 50% through 150%, is data-dependent. So, an exact number can be 
obtained only by testing with your data. 
For example, 100,000 documents of 20 KB each can require about 1500 MB (100,000 x 
20 KB x 75%) of disk space. 
The size of the index is not limited. However, when data is added to or removed from a text 
index, the text index structure is merged to improve query performance. The required 
processing time to complete the merger depends on several factors, such as index size and 
absolute throughput (which in turn depends on the data type and index format). These factors 
result in practical limits on the total text index size.
For query performance, the biggest impact is the number of matching results, not the size of 
the text index.
Temporary disk storage
During the indexing process, the server requires additional disk space for temporary storage. 
The maximum required disk space is approximately four times the total size of the text of the 
documents that are indexed.
Index location
The full text index is stored within the installation directories of the FTS Server. The default 
directory is shown:
<FTS_Home>/config/collections/<collection_name>/data/text
Tip: To determine the text size for AFP and Line Data documents, extract a sample 
document and use the arsview server command to determine the text size.