Improve performance of regexp matching in the sqlite adapter

CHANGELOG

@@ -24,6 +24,8 @@
 
 * Add auto_cast_date_and_time extension, for casting date and time values using SQL standard functions (jeremyevans)
 
+* Cache regexp objects in the sqlite adapter to improve performance (paddor)
+
 === 5.75.0 (2023-12-01)
 
 * Make any_not_empty? extension support passing pattern argument to any? (jeremyevans) (#2100)

doc/opening_databases.rdoc

@@ -388,8 +388,8 @@ The following additional options are supported:
 :readonly :: open database in read-only mode
 :timeout :: the busy timeout to use in milliseconds (default: 5000).
 :setup_regexp_function :: Whether to setup a REGEXP function in the underlying SQLite3::Database object. Doing so
-                          allows you to use regexp support in dataset expressions.  Note that this creates a new
-                          Regexp object per call to the function, so it is not an efficient implementation.
+                          allows you to use regexp support in dataset expressions.  Note that this caches each
+                          unique regex in the database instance.
 
 Note that SQLite memory databases are restricted to a single connection by
 default.  This is because SQLite does not allow multiple connections to

lib/sequel/adapters/sqlite.rb

@@ -126,8 +126,9 @@ def connect(server)
         connection_pragmas.each{|s| log_connection_yield(s, db){db.execute_batch(s)}}
 
         if typecast_value_boolean(opts[:setup_regexp_function])
+          @regexp_cache = Hash.new{|h,k| h[k] = Regexp.new(k)}
           db.create_function("regexp", 2) do |func, regexp_str, string|
-            func.result = Regexp.new(regexp_str).match(string) ? 1 : 0
+            func.result = @regexp_cache[regexp_str].match(string) ? 1 : 0
           end
         end