Calibre :
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Version : 1.21.0 (newest as in 21/01/2014)
OS :
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http://imgur.com/DhISPKb
RAM : 4 GBs
Windows 7 64-bit
Library :
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Amount : ~21000 books
Formats : PDF, DJVU, CHM
Problem :
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http://imgur.com/lZtAHQd
368Mbs of RAM used
So, is this normal memory consumption for this amount of books ???
Even when opening, 368Mbs are consumed.