Julian Hyde created CALCITE-5914:
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Summary: Cache compiled regular expressions in SQL function runtime
Key: CALCITE-5914
URL: https://issues.apache.org/jira/browse/CALCITE-5914
Project: Calcite
Issue Type: Bug
Reporter: Julian Hyde
Cache compiled regular expressions (and other amortized work) in SQL function
runtime.
Consider the following query:
{code}
SELECT ename, job, RLIKE(ename, 'A.*'), RLIKE(ename, job || '.*')
FROM emp
{code}
The first regular expression, {{A.*}}, is constant and can be compiled at
prepare time or at the start of execution; the second regular expression '{{job
|| '.*'}}' might vary from one row to the next. However if the {{job}} column
has a small number of values it still might be beneficial to cache the compiled
regular expression.
If {{SqlFunctions.rlike}} could use a cache (mapping from {{String}} to
{{java.util.regex.Pattern}}) then it would achieve benefits in both the
constant and non-constant cases.
The cache needs to:
* be thread-safe (in case queries are executing using multiple threads),
* return thread-safe objects (as is {{Pattern}}),
* have bounded space (so that a query doesn't blow memory with 1 million
distinct regular expressions),
* disposed after the query has terminated,
* (ideally) share with regexes of the same language in the same query,
* not conflict with regexes of different languages in the same query.
One possibility is to add an {{interface FunctionState}}, with subclasses
including {{class RegexpCache}}, and if argument 1 of a function is a subclass
of {{FunctionState}} the compiler would initialize the state in the generated
code. The function can rely on the state argument being initialized, and being
the same object from one call to the next. Example:
{code}
interface FunctionState {
}
class RegexpCache implements FunctionState {
final Cache<String, Pattern> cache = ...;
}
{code}
This change should install the cache for all applicable functions, including
LIKE, ILIKE, RLIKE, SIMILAR, posix regex, REGEXP_CONTAINS, REGEXP_REPLACE,
other REGEXP_ functions, PARSE_URL.
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