----- Original Message -----
From: "Simon Slavin" <slav...@bigfraud.org>
To: <phi...@blastbay.com>; "General Discussion of SQLite Database"
<sqlite-users@sqlite.org>
Sent: Thursday, June 06, 2013 12:15 AM
Subject: Re: [sqlite] Serialize an in-memory database
On 5 Jun 2013, at 8:38pm, Philip Bennefall <phi...@blastbay.com> wrote:
On 5 Jun 2013, at 8:32pm, Petite Abeille <petite.abei...@gmail.com> wrote:
write to tmpfs… read the file into byte[]… do what you meant to do… to
reload… write byte[] do tmpfs… open db… and be merry… or something along
these lines...
I don't want it in a file, however. I want it in a memory block.
That's why you read from tmpfs (or any other file stored in any other file
system) into byte[]. Once your data is in byte[] you will have entire
SQLite database in one run of memory.
You can't usefully store a memory database of SQLite because SQLite's data
in memory isn't all in one big run of memory. The data is stored in various
little chunks, some here, some there. If you tried to read the data directly
out of those chunks you would have to read lots of little chunks, not one
big run of continuous memory. And you'd be storing lots of pointers to
various locations in memory. When you 'restore' the data back into memory
you're not going to be allocated the same locations in memory so those
pointers won't mean anything any more.
A database stored in a file, however, has pointers to locations in that file
instead of pointers to locations in memory. If you save and restore the
whole file in one big run, those pointers will become valid again: the same
bits of data will be at the same offsets of the file.
Doesn't have to be tmpfs. You can use any file system that SQLite thinks is
file storage rather than memory storage.
Simon.
Hi Simon,
Since I don't believe that Windows for example has tmpfs (seems to be a Unix
thing), would the idea of constructing a vfs that just reads and writes a
huge memory block be doable? If so, how difficult of a task do you estimate
that this might be? I want to reuse as much of the existing vfs code as
possible (e.g. I don't want to reimplement randomness, date etc). Could you
possibly give me some pointers? I read the chapter about the virtual file
systems, but it seems incomplete.
Kind regards,
Philip Bennefall
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