Your guess is wrong.

"pragma cache_size=2000" will limit the internal page cache to 2000 PAGES (of 
whatever page size the db file has) PER OPEN FILE. To set a limit of 2000kBytes 
PER OPEN FILE, use "pragma cache_size=-2000". The page cache is process private 
memory. Whatever portion is actually loaded into main memory (the RSS) counts 
towards PSS.

"pragma mmap_size=N" will limit the number of bytes that will be mapped into 
memory PER OPEN FILE. Memory mapped files may be shared between processes. Note 
that each process gets to determine which part(s) of a file it wants to map. 
Whatever portion of the file is actually loaded into main memory (the RSS) 
counts towards the PSS of all connected processes, divided by the number of 
processes sharing that specific page (on a page per page basis).

If you are running only 1 process AND it has page faulted the whole mmap 
segment into main memory, all of that counts towards PSS.
If you are running 2 processes AND they have mmaped the same region of the same 
file AND they have page faulted the whole segment into main memory, each 
process is held accountable for HALF of that size.

Reducing PSS via mmap is only possible if you are runnning multiple copies of 
the same application against the same db file.

There is no way to directly influence the PSS of a process, since that partly 
depends on ALL of the other processes.

-----Urspr√ľngliche Nachricht-----
Von: sqlite-users [mailto:sqlite-users-boun...@mailinglists.sqlite.org] Im 
Auftrag von Nick
Gesendet: Mittwoch, 11. April 2018 08:52
An: sqlite-users@mailinglists.sqlite.org
Betreff: [EXTERNAL] [sqlite] Does mmap increase PSS?

Hi,
I guess that "cache_size=2000" means PSS of my process will always less than 2M.
But, when I use PRAMGA mmap_size to enable mmap, I found the PSS of my process 
will almost the same as my db.
Is that correct?



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___________________________________________
 Gunter Hick | Software Engineer | Scientific Games International GmbH | 
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