On 09/26/2012 05:48 AM, Simon Slavin wrote:
On 25 Sep 2012, at 10:54pm, David Barrett<dbarr...@expensify.com>
wrote:
If my database is X GB, and the WAL file is Y GB, how much total
disk space is required to:
1) Checkpoint the database
I think it's a maximum of X+Y+Y (including the existing X+Y) plus or
minus a page or two.
2) Vacuum the database
I think it's a maximum of 3*(X+Y) (including the existing X+Y) plus
or minus a page or two. It might be 2*(X+Y). I'm not certain how of
how checkingpointing is done. Both of those answers are dependent on
the database not being corrupt, and SQLite being in a proper working
state.
Additionally, if there are any temporary files created, where do
they exist? We've done some poking around and are having some
crazy theory about a temporary file being created inside /tmp, but
in a *deleted* state.
As far as I know, SQLite does not intentionally play tricks like
that. Your OS may report the length of a temporary file as zero
because it's still open, but SQLite is just using the normal file
writing calls.
Actually it might. On unix, if you unlink a file while one or more
clients have it open, the clients can keep reading and writing the
file descriptor. No other can open the file though (as it is not
linked into the file-system). So when SQLite requires a temporary
file, it normally creates and opens a file with a randomized name
in /tmp then calls unlink() on it immediately - before it starts
using the file.
Dan.
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