Background

The current implementation of Cps Path queries relies on regular expressions in the generated SQL queries.

For example, given this Cps Path:

/bookstore/categories[@code="1"]/books[@title="Matilda"]

the following SQL query is generated:

SELECT
    * 
FROM
    FRAGMENT 
WHERE
    anchor_id = 3
    AND xpath ~ '/bookstore/categories\[@code=''1'']/books(\[@(?!.*\[).*?])?$' 
    AND (
        attributes @> '{"title":"Matilda"}'
    )

The use of regex potentially results in full table scans, severely limiting performance, and causing query time duration to grow linearly with the database size (i.e. queries get slower as the DB gets bigger).

A new algorithm for queries is being proposed, avoiding regex, so that query duration is independent of database size.

Proposal

The new approach involves adding a column to the Fragment table, storing the xpath component.

TODO description of new algorithm

For example, given this Cps Path:

/bookstore/categories[@code="1"]/books[@title="Matilda"]

the following SQL query is generated:

SELECT
    * 
FROM
    fragment 
WHERE
    parent_id IN (
        SELECT
            id 
        FROM
            fragment 
        WHERE
            xpath_component = 'categories[@code=''1'']'
            AND parent_id = (
                SELECT
                    id 
                FROM
                    fragment 
                WHERE
                    xpath_component = 'bookstore'
                    AND anchor_id = 3
                    AND parent_id IS NULL
            )
        ) 
        AND (
            xpath_component = 'books'
            OR xpath_component LIKE 'books[%'
        ) 
        AND (
            attributes @> '{"title":"Matilda"}'
        )

Proof of Concept

A PoC was developed so that performance could be compared against existing Cps Path Query algorithms.

Performance Improvement

As can be seen in the cases below, the existing algorithm using regex has linear time complexity, on the the size of the database. The new algorithm is constant time.

• For querying 1 out of many nodes, existing algorithm is linear
• For querying 1 out of many nodes, existing algorithm is constant
• For querying many out of many nodes, existing algorithm is quadratic
• For querying many out of many nodes, new algorithm is linear

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