Support for creating index with text_pattern_ops

[ebner]

We are using text pattern indexes in jsonb like this:

CREATE INDEX ON data_29cca9f2 ((data->>'json123') text_pattern_ops)

I already found #9682 that tracks support for expression-based index columns, but I failed to find an issue for support of text_pattern_ops. Are there any plans for supporting any of the *_pattern_ops available in PostgreSQL?

Jira issue: CRDB-2839

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[RaduBerinde]

Can you explain why you need text_pattern_ops and what doesn't work if you don't use it? I may be wrong, but I think CRDB's indexes on string work character by character, so you might not need it. CC @jordanlewis who might know more.

[ebner]

We use text_pattern_ops to index arbitrary text values of JSON objects (jsonb type) in order to improve query performance (regex-based queries may happen). In fact, the lack of text_pattern_ops is only one showstopper, we also need the index to be expression-based which is another showstopper. We'd have to work around #9682 by using stored generated columns for every JSON property.

[jordanlewis]

@ebner, would you be able to offer an example query that is only satisfiable with text_pattern_ops? It would help us understand your use case better.

Expression-based indexes are likely to be released in our next major release, this Spring.

[ebner]

The queries are not different from any queries against an index without opclass and our application would not break if we removed the text_pattern_ops, but we want to achieve the best possible performance with our queries. An example query using a regex (data is of type jsonb) is as follows:

SELECT data FROM data_25275cd3 WHERE data->>'prop1' ~ '^För.*'

We chose the opclass because of the statement "The difference from the default operator classes is that the values are compared strictly character by character rather than according to the locale-specific collation rules. This makes these operator classes suitable for use by queries involving pattern matching expressions (LIKE or POSIX regular expressions) when the database does not use the standard “C” locale." in the PostgreSQL documentation on Operator Classes. We do not use the standard C locale and we use regular expressions.

Glad to hear about the upcoming expression-based indexes!

[jordanlewis]

Got it. We will support this kind of query with and without text_pattern_ops once #50345 is finished. Today, we still don't support regex or like matches on inverted indexes, though our index structure supports them.

[ebner]

Great, thanks for the pointer to #50345!

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