Gary Potagal created PDFBOX-4188:
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Summary: "Maximum allowed scratch file memory exceeded."
Exception when merging large number of small PDFs
Key: PDFBOX-4188
URL: https://issues.apache.org/jira/browse/PDFBOX-4188
Project: PDFBox
Issue Type: Improvement
Affects Versions: 2.0.9
Reporter: Gary Potagal
I have been running some tests trying to merge large amounts (2618) of small
pdf documents, between 100kb and 130kb, into a single large pdf (288.433kb)
Memory consumption seems to be the main limitation.
ScratchFileBuffer seems to consume the majority of the memory usage.
(see screenshot from mat in attachment)
(I would include the hprof in attachment so you can analyze yourselves but it's
rather large)
Note that it seems impossible to generate a large pdf using a small memory
footprint.
I personally thought that using MemorySettings with temporary file only would
allow me to generate arbitrarily large pdf files but it doesn't seem to help.
I've run the mergeDocuments with memory settings:
* MemoryUsageSetting.setupMixed(1024L * 1024L, 1024L * 1024L * 1024L * 1024L *
1024L)
* MemoryUsageSetting.setupTempFileOnly()
Refactored version completes with *4GB* heap:
with temp file only completes 2618 documents in 1.760 min
*VS*
*8GB* heap:
with temp file only completes 2618 documents in 2.0 min
Heaps of 6gb or less result in OOM. (Didn't try different sizes between 6GB and
8GB)
It looks like the loop in the mergeDocuments accumulates PDDocument objects in
a list which are closed after the merge is completed.
Refactoring the code to close these as they are used, instead of accumulating
them and closing all at the end, improves memory usage considerably.(although
doesn't seem to be eliminated completed based on mat analysis.)
Another change I've implemented is to only create the inputstream when the file
needs to be read and to close it alongside the PDDocument.
(Some inputstreams contain buffers and depending on the size of the buffers and
or the stream type accumulating all the streams is a potential memory-hog.)
These changes seems to have a beneficial improvement in the sense that I can
process the same amount of pdfs with about half the memory.
I'd appreciate it if you could roll these changes into the main codebase.
(I've respected java 6 compatibility.)
I've included in attachment the java files of the new implementation:
* Suppliers
* Supplier
* PDFMergerUtilityUsingSupplier
PDFMergerUtilityUsingSupplier can replace the previous version. No signature
changes only internal code changes. (just rename the class to PDFMergerUtility
if you decide to implemented the changes.)
In attachment you can also find some screenshots from visualvm showing the
memory usage of the original version and the refactored version as well as some
info produced by mat after analysing the heap.
If you know of any other means, without running into memory issues, to merge
large sets of pdf files into a large single pdf I'd love to hear about it!
I'd also suggest that there should be further improvements made in memory usage
in general as pdfbox seems to consumer a lot of memory in general.
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