Fix quadratic INSERT INTO ... VALUES sanitisation performance
#33
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unflxw
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INSERT INTO ... VALUES sanitisation performance
Since `#[bench]` is nightly-only, add a simple binary that can be modified to test the performance of specific queries as needed.
Using `Vec::remove(i)` causes the `n` tokens between position `i` and the end of the vector to be shifted, which is an `O(n)` operation. When done in a loop, as it is done in our `INSERT INTO ... VALUES` repeated list sanitisation, it makes the overall performance `O(n^2)`. To avoid using `Vec::remove`, implement a `Token::None` value that represents a "non-token", a gap to be ignored in the token list. Replace calls to `Vec::remove(i)` with replacing the token at position `i` with `Token::None`. Replace calls to `Vec::insert` for the same reason -- luckily, when we insert a token, it's a replacement for a different token, so it's possible to rewrite them in that manner. These are rarely done in a loop, though, so the impact on sanitisation performance is much more limited.
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thijsc
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Dec 20, 2024
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Fixes appsignal/appsignal-elixir#975. I introduced this bug in #32.
Add simple benchmark tool
Since
#[bench]is nightly-only, add a simple binary that can bemodified to test the performance of specific queries as needed.
Avoid
Vec::removewithNonetokenUsing
Vec::remove(i)causes thentokens between positioniandthe end of the vector to be shifted, which is an
O(n)operation.When done in a loop, as it is done in our
INSERT INTO ... VALUESrepeated list sanitisation, it makes the overall performance
O(n^2).To avoid using
Vec::remove, implement aToken::Nonevalue thatrepresents a "non-token", a gap to be ignored in the token list.
Replace calls to
Vec::remove(i)with replacing the token atposition
iwithToken::None.Replace calls to
Vec::insertfor the same reason -- luckily, whenwe insert a token, it's a replacement for a different token, so it's
possible to rewrite them in that manner. These are rarely done in a
loop, though, so the impact on sanitisation performance is much more
limited.