Add a test

tests/queries/0_stateless/02458_relax_too_many_parts.reference

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+4	8000000

tests/queries/0_stateless/02458_relax_too_many_parts.sql

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+-- Check that max_parts_to_throw_insert limit work
+
+DROP TABLE IF EXISTS test;
+CREATE TABLE test (x UInt64, s String) ENGINE = MergeTree ORDER BY tuple() SETTINGS parts_to_throw_insert = 3;
+
+-- The "too many parts" threshold works:
+SET max_block_size = 1, min_insert_block_size_rows = 1, min_insert_block_size_bytes = 1;
+SYSTEM STOP MERGES test;
+INSERT INTO test VALUES (1, 'a');
+INSERT INTO test VALUES (2, 'a');
+INSERT INTO test VALUES (3, 'a');
+INSERT INTO test VALUES (4, 'a'); -- { serverError TOO_MANY_PARTS }
+
+-- But it can be relaxed with a setting:
+ALTER TABLE test MODIFY SETTING max_avg_part_size_for_too_many_parts = '1M';
+
+-- It works in the same way if parts are small:
+SYSTEM START MERGES test;
+OPTIMIZE TABLE test FINAL;
+SYSTEM STOP MERGES test;
+
+INSERT INTO test VALUES (5, 'a');
+INSERT INTO test VALUES (6, 'a');
+INSERT INTO test VALUES (7, 'a'); -- { serverError TOO_MANY_PARTS }
+
+-- But it allows having more parts if their average size is large:
+SYSTEM START MERGES test;
+OPTIMIZE TABLE test FINAL;
+SYSTEM STOP MERGES test;
+
+SET max_block_size = 65000, min_insert_block_size_rows = 65000, min_insert_block_size_bytes = '1M';
+INSERT INTO test SELECT number, randomString(1000) FROM numbers(0, 10000);
+INSERT INTO test SELECT number, randomString(1000) FROM numbers(10000, 10000);
+INSERT INTO test SELECT number, randomString(1000) FROM numbers(20000, 10000);
+
+SELECT count(), round(avg(bytes), -6) FROM system.parts WHERE database = currentDatabase() AND table = 'test' AND active;
+
+DROP TABLE test;