Array Library

The array library offers easy allocation of large memory mapped files with less performance overhead than the traditional buffers[i].get(j)-style constructions java often leads to given its suffocating 2 Gb ByteBuffer size limitation.

It accomplishes this by delegating block oerations down to the appropriate page. If the operation crosses a page boundary, it is not delegated and a bit slower.

It's a very C++-style library that does unidiomatic things with interface default functions to get diamond inheritance.

Quick demo:

var array = LongArray.mmapForWriting(Path.of("/tmp/test"), 1<<16);

array.transformEach(50, 1000, (pos, val) -> Long.hashCode(pos));
array.quickSort(50, 1000);
if (array.binarySearch(array.get(100), 50, 1000) >= 0) {
    System.out.println("Nevermind, I found it!");
}

array.range(50, 1000).fill(0, 950, 1);
array.forEach(0, 100, (pos, val) -> {
    System.out.println(pos + ":" + val);
});

Query Buffers

The library offers many operations for sorting and dealing with sorted data. The classes IntQueryBuffer and LongQueryBuffer are used heavily in the search engine's query processing.

They are dual-pointer buffers that offer tools for filtering data.

LongQueryBuffer buffer = new LongQueryBuffer(1000);

fillBuffer(buffer);

// A typical filtering operation may look like this:
        
while (buffer.hasMore()) { // read < end
    if (someCondition(buffer.currentValue())) {
        // copy the value pointed to by the read
        // pointer to the read pointer, and
        // advance both
        buffer.retainAndAdvance();
    }
    else {
        // advance the read pointer
        buffer.rejectAndAdvance();
    }
}

// set the read pointer to the read pointer
// after this we can filter again

buffer.finalizeFiltering();

Especially noteworthy are the operations retain() and reject() in IntArraySearch and LongArraySearch. They keep or remove all items in the buffer that exist in the range. These are used to offer an intersection operation for the B-Tree that has in practice sub-linear run time.

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Array Library

Quick demo:

Query Buffers

2.4 KiB

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