Hi,
I had a look at the BitField class as well. I still use a long array
for getLastSetBit(), nextSetBit(), nextClearBit(). But set and get a
byte at a time. My tests shows it's about 8 time faster. This will be
included in the next release. If you want, you can already test it,
the source code is in subversion at
http://code.google.com/p/h2database/source/checkout
Of course you can also send your version, it's always interesting to
compare two approaches.
Regards,
Thomas
On Tue, Oct 14, 2008 at 3:30 PM, Alex <[EMAIL PROTECTED]> wrote:
>
> Hello Thomas,
>
> I could send you my quick and dirty version of the BitField class. In
> our initial tests with large databases (300+ MB) the BitField
> operations were taking 70% of the Database.open time.
> The actual file IO was not even on the picture. When we used the
> modified BitField ( and a couple of small changes to the DiskFile
> class) the file IO came up and became the slowest operation.
>
> Alex
>
>
> On Oct 13, 3:19 pm, "Thomas Mueller" <[EMAIL PROTECTED]>
> wrote:
>> 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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