On 12/22/15, ??? <2004wqg2008 at 163.com> wrote: > What do you mean of "render the mmap_size mote "?
The "PRAGMA mmap_size" command sets the operating-system interface into a mode so that at calls mmap() to read content from disk rather than calling read(). It is often faster to use mmap() because that avoids having to copy content from kernel space into user space. However, mmap() mode only works if the database is reading exactly the same content as is present on disk. In the case of ZIPVFS, the content on disk is compressed and encryption. The content on disk is different from the content used by the database engine. The content has to be converted when moving from disk into the application and when moving from the application to the disk. Because the content in the application is different from the content on disk, mmap() won't work. And so when using ZIPVFS, the "PRAGMA mmap_size=NNN" command is a no-op. -- D. Richard Hipp drh at sqlite.org
