Hello, Thank you again for a great library.
We wanted to address one more merge issue in org.apache.pdfbox.multipdf.PDFMergerUtility#mergeDocuments(org.apache.pdfbox.io.MemoryUsageSetting). We need to merge a large number of small files. We use mixed mode, memory and disk for cache. Initially, we would often get "Maximum allowed scratch file memory exceeded.", unless we turned off the check by passing "-1" to org.apache.pdfbox.io.MemoryUsageSetting#MemoryUsageSetting. I believe, this is what the users that opened https://issues.apache.org/jira/browse/PDFBOX-3721 where running into. Our research indicates that the core issue with the memory model is that instead of sharing a single cache, it breaks it up into equal sized fixed partitions based on the number of input + output files being merged. This means that each partition must be big enough to hold the final output file. When 400 1-page files are merged, this creates 401 partitions, but each of which needs to be big enough to hold the final 400 pages. Even worse, the merge algorithm needs to keep all files open until the end. Given this, near the end of the merge, we're actually caching 400 x 1-page input files, and 1 x 400-page output file, or 801 pages. However, with the partitioned cache, we need to declare room for 401 x 400-pages, or 160,400 pages in total when specifying "maxStorageBytes". This would be a very high number, usually in GIGs. Given the current limitation that we need to keep all the input files open until the output file is written (HUGE), we came up with 2 options. 1. Good: Split the cache in ½, give ½ to the output file, and segment the other ½ across the input files. (Still keeping them open until then end). 2. Better: Dynamically allocate in 16 page (64K) chunks from memory or disk on demand, release cache as documents are closed after merge. This is our current implementation till PDFBOX-3999 is addressed. We would like to submit our current implementation as a Patch to 2.0.10, unless this is already addressed. Thank you This email, including attachments, may contain information that is privileged, confidential or is exempt from disclosure under applicable law (including, but not limited to, protected health information). It is not intended for transmission to, or receipt by, any unauthorized persons. If the reader of this message is not the intended recipient, or the employee or agent responsible for delivering the message to the intended recipient, you are hereby notified that any dissemination, distribution or copying of this communication is strictly prohibited. If you believe this email was sent to you in error, do not read it. Please notify the sender immediately informing them of the error and delete all copies and attachments of the message from your system. Thank you.
