fix SplitTokenExtractor::nextInStringLike skipping tokens

[ozcelgozde]

We are using a lot of like searches with tokenbf index and I was noticing the performance was really bad. After looking through the code and also seeing a few more issues opened here, I noticed SplitTokenExtractor::nextInStringLike skips some crucial tokens. For example if i do a search like this: body like '%test%', test as a token is completely skipped and this becomes a full db scan. Also other issues: 72065 and 68985. Not sure how to proceed from here so some feedback would be appreciated.

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Refactored token extraction logic to ensure valid tokens are not prematurely reset by wildcards (% or _)

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[nikitamikhaylov]

@ozcelgozde A test would be very appreciated. But also these extractors available as functions and I don't see a problem here:

» clickhouse
ClickHouse local version 25.1.1.1.

:) select tokens('%test%')

SELECT tokens('%test%')

Query id: 4586894c-9bd4-4748-b312-a4b35a0522d0

   ┌─tokens('%test%')─┐
1. │ ['test']         │
   └──────────────────┘

1 row in set. Elapsed: 0.002 sec.

And the tests have failed...

[ozcelgozde]

@nikitamikhaylov hey thanks for the reply. This case only happens during bloom filter (tokenbf_v1) index calculation so regular tokens function is not hitting that. I see the tests related to that areas are failing so I will take a look at them.
First failing test is inserting strings like:

hhhhhhhhhhhhhhhhhhhhhhhhhxxxxxxxxxxxxxxxxxxxxxxxxxxxxyyyyyyyyyyyyyyyyyyyyyyyyyy1342957354
hhhhhhhhhhhhhhhhhhhhhhhhhxxxxxxxxxxxxxxxxxxxxxxxxxxxxyyyyyyyyyyyyyyyyyyyyyyyyyy3487425490

then tries to do token search with like '%x%' but since tokens('hhhhhhhhhhhhhhhhhhhhhhhhhxxxxxxxxxxxxxxxxxxxxxxxxxxxxyyyyyyyyyyyyyyyyyyyyyyyyyy1342957354
') does not divide this long string and its a single token, then

SELECT COUNT() FROM indexed_table WHERE log_message like '%x%';

this not returning any value is valid wdyt?

Before this PR this statement:

like '%x%'

was skipping x as a token thats why tests were returning all 1000 values

[alexey-milovidov]

@ozcelgozde Check the tests.

[clickhouse-gh]

Dear @alexey-milovidov, this PR hasn't been updated for a while. You will be unassigned. Will you continue working on it? If so, please feel free to reassign yourself.

[EmeraldShift]

SELECT COUNT() FROM indexed_table WHERE log_message like '%x%'; 

this not returning any value is valid wdyt?

This sounds invalid to me. LIKE is a substring search, not a token search, so I would expect 'axe' LIKE '%x%' to return 1. If the skip index were used to filter only granules with a standalone x token, it would incorrectly skip granules containing x as part of a larger token.

In your original example, a search LIKE '%test%' matches a value like the tests are passing, but restricting only to granules containing token test would skip it incorrectly.

Recently I think there is a new function hasToken that should more accurately map to the queries it sounds like you're expecting.

[alexey-milovidov]

@EmeraldShift, yes, exactly! And we introduced these new functions recently.