Fast scan of a vector of properties of consecutive node IDs in columns

[semihsalihoglu-uw]

At the time of writing our main column scan operator uses the following function from column.cpp:

void Column::readValues(
    const shared_ptr<ValueVector>& nodeIDVector, const shared_ptr<ValueVector>& valueVector) {
    assert(nodeIDVector->dataType.typeID == NODE);
    if (nodeIDVector->state->isFlat()) {
        auto pos = nodeIDVector->state->getPositionOfCurrIdx();
        readForSingleNodeIDPosition(pos, nodeIDVector, valueVector);
    } else {
        for (auto i = 0ul; i < nodeIDVector->state->selectedSize; i++) {
            auto pos = nodeIDVector->state->selectedPositions[i];
            readForSingleNodeIDPosition(pos, nodeIDVector, valueVector);
        }
    }
}

void Column::readForSingleNodeIDPosition(uint32_t pos, const shared_ptr<ValueVector>& nodeIDVector,
    const shared_ptr<ValueVector>& resultVector) {
    if (nodeIDVector->isNull(pos)) {
        resultVector->setNull(pos, true);
        return;
    }
    auto pageCursor = PageUtils::getPageElementCursorForOffset(
        nodeIDVector->readNodeOffset(pos), numElementsPerPage);
    auto frame = bufferManager.pin(fileHandle, pageCursor.idx);
    memcpy(resultVector->values + pos * elementSize,
        frame + mapElementPosToByteOffset(pageCursor.pos), elementSize);
    setNULLBitsForAPos(resultVector, frame, pageCursor.pos, pos);
    bufferManager.unpin(fileHandle, pageCursor.idx);
}

That is, for each node in the vector, we read it's value, which attempts to pin a page through the BM, so acquires a lock etc. This is quite inefficient for the case when the given nodeIDs are consecutive and many of them can be scanned in chunks. We need a fast path to be able to perform these fast scans.

[andyfengHKU]

Fixed in PR #627