On 28 May 2018, at 7:56pm, Torsten Curdt <[email protected]> wrote:
> Just to clarify: I have a single thread - so intermixing the stepping
> through a resultset and doing an update requires WAL mode but should be
> fine. Correct?
Yes, this should work fine. Obviously, one thread is not going to be trying to
do two database accesses at the same time, especially since your software
design uses the result from one SELECT row in order to figure out what UPDATE
to issue.
You could, course, build up an array of pairs in memory while doing the SELECT,
then consult the array to create all the UPDATE commands once you have
finalized the SELECT. If you do do this don't forget to surround the UPDATE
commands with BEGIN;...COMMIT; .
One technique I have used in a similar situation was to write all my UPDATE
commands to a long text buffer. This was in an unusual situation where I
needed to get the SELECT done as quickly as possible to avoid locking up lab
equipment. So the software figured out all the UPDATE commands and
concatenated them in a text variable:
UPDATE for_row_1;UPDATE for_row_2;UPDATE for_row_3;...
The buffer could get as big as half a megabyte or so. Then I sqlite3_reset()
the SELECT command. Then I submit the entire piece of text as one long
parameter to sqlite3_exec(). Worked perfectly, very quickly, and didn't take
up much more memory than storing the parameters in an array.
Simon.
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