Ben Manes created PDFBOX-4668:
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Summary: Add ResourceCacheFactory as global setting
Key: PDFBOX-4668
URL: https://issues.apache.org/jira/browse/PDFBOX-4668
Project: PDFBox
Issue Type: Task
Components: Rendering
Reporter: Ben Manes
Attachments: memory.png, threads.png
Image rendering is cached by {{DefaultResourceCache}} per-document using soft
references. As described in the [FAQ|https://pdfbox.apache.org/2.0/faq.html],
this can lead to an {{OutOfMemoryError}} when processing, e.g. many documents
in parallel. The configuration of this cache is per-document and it is
initialized with the default.
{code}
// document-wide cached resources
private ResourceCache resourceCache = new DefaultResourceCache();
{code}
This requires all call sites be modified to disable it, some of which may be in
3rd party code. The ask is to static factory to configure the default globally,
which would return a new {{DefaultResourceCache}} when called. This would let a
user specify a new static factory, e.g. one that returns a custom cache or
{{null}} if disabled.
Soft references are a problematic caching scheme, which degrades poorly. It is
very likely that the many and large image fragments causes GC promotion
(eden=>young=>old) which requires a full GC to collect. Under memory/cpu
pressure, the GC can devolve into a death spiral of collecting the minimal heap
space to match its pause time constraints, leading to repeated GCs due to soft
reference pollutions and an eventual OOME. If caching was set, it might be
preferable to be size-based (by rough byte-size) and perhaps tied into
{{MemoryUsageSetting}} main memory configuration.
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