[PDFBOX-5602] Consider adding support for PDF files Concatenation in addition to the full Merge

• Type: New Feature
• Status: Closed
• Priority: Major
• Resolution: Won't Do
• Affects Version/s: 3.0.0 PDFBox
• Component/s: Utilities
• Assignee: Unassigned
• Reporter: Zbigniew Minciel
• Created: 12/May/23 06:51
• Updated: 18/May/23 05:41
• Resolved: 18/May/23 05:41

Description

I decided to evaluate pdfbox 3.0.0-alpha3 limits on merging large number of PDF files.

I attempted to merge 7500 mails in separate PDF files on Windows. Given the limitation on the max size of the command line arguments, I was merging subsets of files. I ended up with 5 large PDF files, each around 500-600MBytes. I tried to merge these 5 files but eventually merge failed after running more than 6 hours.  See error log at the bottom. I have large RAM 48GBytes.  PDFBox was using up 13GB of memory max. Usage was changing between 600MB and 13Gb. 

I am wondering whether PDFBox could support Concatenation mode in addition to the full Merge mode.  No need to create index table, etc. It could work as follow I suppose given my total lack of understanding how PDF works:

1. Read first file, process and append to the target PDF file. Delete PDF data and related meta data for this file except perhaps the last page number.
2. Read the second file and process in similar fashion as in the step 1
3. etc

If Concatenation is possible, it would greatly reduce the cpu and memory overhead and reduce processing time.

I admit merging of such large number of PDF files is not typical but the issue is valid.

^CException in thread "main" java.lang.OutOfMemoryError: Java heap space
    at java.base/java.util.Hashtable.rehash(Hashtable.java:419)
    at java.base/java.util.Hashtable.addEntry(Hashtable.java:441)
    at java.base/java.util.Hashtable.put(Hashtable.java:493)
    at org.apache.pdfbox.pdfwriter.COSWriter.doWriteBodyCompressed(COSWriter.java:481)
    at org.apache.pdfbox.pdfwriter.COSWriter.visitFromDocument(COSWriter.java:1260)
    at org.apache.pdfbox.cos.COSDocument.accept(COSDocument.java:402)
    at org.apache.pdfbox.pdfwriter.COSWriter.write(COSWriter.java:1542)
    at org.apache.pdfbox.pdfwriter.COSWriter.write(COSWriter.java:1418)
    at org.apache.pdfbox.pdmodel.PDDocument.save(PDDocument.java:1018)
    at org.apache.pdfbox.pdmodel.PDDocument.save(PDDocument.java:963)
    at org.apache.pdfbox.pdmodel.PDDocument.save(PDDocument.java:982)
    at org.apache.pdfbox.multipdf.PDFMergerUtility.legacyMergeDocuments(PDFMergerUtility.java:476)
    at org.apache.pdfbox.multipdf.PDFMergerUtility.mergeDocuments(PDFMergerUtility.java:355)
    at org.apache.pdfbox.multipdf.PDFMergerUtility.mergeDocuments(PDFMergerUtility.java:339)
    at org.apache.pdfbox.tools.PDFMerger.call(PDFMerger.java:76)
    at org.apache.pdfbox.tools.PDFMerger.call(PDFMerger.java:37)
    at picocli.CommandLine.executeUserObject(CommandLine.java:1953)
    at picocli.CommandLine.access$1300(CommandLine.java:145)
    at picocli.CommandLine$RunLast.executeUserObjectOfLastSubcommandWithSameParent(CommandLine.java:2358)
    at picocli.CommandLine$RunLast.handle(CommandLine.java:2352)
    at picocli.CommandLine$RunLast.handle(CommandLine.java:2314)
    at picocli.CommandLine$AbstractParseResultHandler.execute(CommandLine.java:2179)
    at picocli.CommandLine$RunLast.execute(CommandLine.java:2316)
    at picocli.CommandLine.execute(CommandLine.java:2078)
    at org.apache.pdfbox.tools.PDFBox.main(PDFBox.java:76)

Respectfully,

Zbigniew