On Friday 16 September 2005 15:53, Russell Howe wrote:
> While browsing the SQLite docs, to see how to find out what indices are
> on a table ( the answer is '.schema <tablename>' ), I came across this.
>
> Kern, perhaps this is why SQLite 3.0 seems so slow for you?
>
> PRAGMA synchronous;
> PRAGMA synchronous = FULL; (2)
> PRAGMA synchronous = NORMAL; (1)
> PRAGMA synchronous = OFF; (0)
>
> Query or change the setting of the "synchronous" flag. The first (query)
> form will return the setting as an integer. When synchronous is FULL
> (2), the SQLite database engine will pause at critical moments to make
> sure that data has actually been written to the disk surface before
> continuing. This ensures that if the operating system crashes or if
> there is a power failure, the database will be uncorrupted after
> rebooting. FULL synchronous is very safe, but it is also slow. When
> synchronous is NORMAL, the SQLite database engine will still pause at
> the most critical moments, but less often than in FULL mode. There is a
> very small (though non-zero) chance that a power failure at just the
> wrong time could corrupt the database in NORMAL mode. But in practice,
> you are more likely to suffer a catastrophic disk failure or some other
> unrecoverable hardware fault. With synchronous OFF (0), SQLite continues
> without pausing as soon as it has handed data off to the operating
> system. If the application running SQLite crashes, the data will be
> safe, but the database might become corrupted if the operating system
> crashes or the computer loses power before that data has been written to
> the disk surface. On the other hand, some operations are as much as 50
> or more times faster with synchronous OFF.
>
> In SQLite version 2, the default value is NORMAL. For version 3, the
> default was changed to FULL.
Yes, this would definitely create the slow down problem I saw. I'll run some
timings to confirm it, document it, and probably set the default to NORMAL.
Thanks for the insight.
--
Best regards,
Kern
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