Handling XSL:FO’s memory issue with large page counts
Formatting Object (FO) processors (FOP, in particular) often fail with memory errors when processing very large documents for PDF output. Typically in XSL:FO, the body of a document is contained in a single fo:page-sequence element. When FO documents are converted to PDF output, the FO processor holds an entire fo:page-sequence in memory to perform pagination adjustments over the span of the sequence. Very large page counts can result in memory overflows or Java heap space errors. Reducing page count in a document is not usually an option.
You can set up processing to divide the document into multiple fo:page sequences to avoid memory problems. The granularity of the content of each fo:page-sequence does not matter. Each fo:page-sequence could contain a chapter, a sub-chapter, a section, and so on. For a DITA implementation, each DITA topic could be placed in its own page sequence. The key is to place elements in a flat sequence of fo:page-sequences.
Flattening the hierarchy is challenging. The examples in this document will explain the approach.
| NOTE: | This document assumes basic familiarity with XSL, XSL:FO, DITA, and the DITA Open Toolkit. |
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Considerations in
creating multiple page sequences