Resolve todo "Blob pattern search is slow"

[nell-shark]

See Todo

If you would like to save a previous code:

BufferedInputStream in = new BufferedInputStream(value.getInputStream());
IOUtils.skipFully(in, start - 1);
int pos = 0;
int patternPos = 0;
while (true) {
    int x = in.read();
    if (x < 0) {
        break;
    }
    if (x == (pattern[patternPos] & 0xff)) {
        if (patternPos == 0) {
            in.mark(pattern.length);
        }
        if (patternPos == pattern.length) {
            return pos - patternPos;
        }
        patternPos++;
    } else {
        if (patternPos > 0) {
            in.reset();
            pos -= patternPos;
        }
    }
    pos++;
}
return -1;

I think you need to update code as follows:

if (patternPos == (pattern.length -1)) {
  return pos - patternPos;
}

and:

if (patternPos > 0) {
  in.reset();
  pos -= patternPos;
  patternPos = 0;
}

[katzyn]

Thank you for your contribution!

This method is unconditionally disabled in H2, there is no way to use it without recompliation of H2 with modified sources and it seems that nobody cares, this method doesn't look like being really useful.

If you really want to improve it, you also need to remove Constants.BLOB_SEARCH and related conditions and add some real tests for both Blob.position() methods to TestLobApi, including tests with invalid arguments.

ArrayList<Byte> also isn't suitable for efficient implementations.

[nell-shark]

@katzyn, Thank you for your quick feedback