Hi,
Thank for your help! I will have a look how this can be improved.
Maybe it makes sense to use int or byte, but I want to make sure it
does in fact get faster so I will need to write some benchmarks as
well.
Regards,
Thomas
On Sat, Oct 11, 2008 at 12:00 AM, Alex <[EMAIL PROTECTED]> wrote:
>
> We were looking at some profiles running on large databases and
> noticed that under some circumstances BitField operations are taking a
> large percentage of time when opening the database.
>
> Particularly the BitField class is implemented using "long" data type
> for bit storage. However when it gets used from the DiskFile class
> getSummary() and initFromSummary() methods they are using bytes. The
> code there basically moves the data from the longs into the bytes bit
> by bit which is very inefficient. It would be very easy to modify the
> BitField class to utilize the byte[] for storage and use this byte[]
> directly to store/restore the allocation table.
>
> We also noticed that sometimes the BitField.setRange method is also
> taking considerable time.
> I guess there should be a way to optimize it as well using byte/long
> operations rather than iterating the range bit by bit.
>
> Below are the code snippets in question:
>
> initFromSummary:
> ======================================================
> for (int i = 0, x = 0; i < b2 / 8; i++) {
> int mask = in.read();
> if (init) {
> for (int j = 0; j < 8; j++, x++) {
> if (used.get(x) != ((mask & (1 << j)) !=
> 0)) {
> throw Message.getInternalError("Redo
> failure, block: " + x + " expected in-use bit: " + used.get(x));
> }
> }
> } else {
> for (int j = 0; j < 8; j++, x++) {
> if ((mask & (1 << j)) != 0) {
> used.set(x);
> }
> }
> }
> }
> ======================================================
>
> getSummary()
>
> ======================================================
> for (int i = 0, x = 0; i < blocks / 8; i++) {
> int mask = 0;
> for (int j = 0; j < 8; j++) {
> if (used.get(x)) {
> mask |= 1 << j;
> }
> x++;
> }
> out.write(mask);
> }
> ====================================================
>
> >
>
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