Hi Noel,
Thanks for the suggestion to increase page size. Something I'll consider.
I took another look at code I asked about. It seems to me this is what
happens:
1) load first 16 bytes of a data page from disk
2) if the first of those 16 loaded bytes is not 0, then zero the entire
page, as follows: (comments are mine)
// move to start of page i
file.seek((long) i << pageSizeShift);
// zero out entire contents of page i
file.write(empty, 0, pageSize);
Experience has taught me that sections of code like this usually have a
very good reason. Alas, I can't work out that reason yet.
Thomas, can you illuminate?
Regards
Steve
On Tuesday, 3 April 2012 13:45:34 UTC+2, Noel Grandin wrote:
>
> I can't be sure, but it looks like it's zero-ing out the header of a
> page, so I would assume that it's a little necessary.
>
> you could try increasing the page size of your database, that might
> speed up this operation.
>
>
> On 2012-04-02 17:15, Steve McLeod wrote:
> > Hi Thomas,
> >
> > When running TRUNCATE TABLE on a large table, it is time-consuming.
> > I've done some profiling of the H2 source, and found that a step in
> > PageStore.checkpoint() that consumes one-third of the time needed for
> > TRUNCATE TABLE. In my specific case it uses 69 seconds out of seconds
> > for the whole TRUNCATE execution.
> >
> > This line is the one consuming the time:
> >
> > file.readFully(test, 0, 16);
> >
> > which is org.h2.store.PageStore.java: line 451 in the current SVN trunk.
> >
> > It is part of a process of zeroing freed pages on disk. I'm wondering
> > if zeroing is an important part of the workings of the PageStore. Or
> > is it for security reasons? If so, is this step something I could
> > potentially make optional by introducing a "INSECURE_FREE" database
> > option?
> >
> > I'm running on Mac OS X Lion, using an SSD drive.
> >
> > Regards,
> >
> > Steve McLeod
> >
> >
> >
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