sql: logic_test/crdb_internal: add missing comments

pkg/sql/logictest/testdata/logic_test/crdb_internal

@@ -435,18 +435,31 @@ subtest max_retry_counter
 statement ok
 SET application_name = 'test_max_retry'
 
+# Make the statement retry, to ensure max_retries increases to
+# become different from 0.
+# The delay is chosen identically to the value in the `txn`
+# logic tests introduced in #16719. It is long enough
+# to ensure max_retries increases, even under stress,
+# but short enough to be negligible compared to the
+# overall test suite.
 statement OK
 SELECT crdb_internal.force_retry('50ms'::INTERVAL)
 
 statement OK
 RESET application_name
 
-# Note: two rows of output are expected: one for the statement that
-# failed with a retry error, and one for the final retry attempt that
-# succeeded without an error.
-# We also expect the RESET statement to not have any retry.
-# This tests that the retry counter is properly reset to 0
-# between statements.
+# Note: in the following test, three rows of output are expected:
+# - one for the SELECT statements that failed with a retry error,
+# - one for the final SELECT retry attempt that succeeded without an error,
+# - one for the RESET statement.
+#
+# We expect the first two entries to have max_retries > 0 because
+# auto-retries are expected by the server.
+# We also expect the RESET statement to have max_retries = 0, because
+# RESET never retries. This tests that the retry counter is properly
+# reset to 0 between statements - a naive implementation could make
+# the counter increase forever, even between statements.
+#
 query TBB
 SELECT key, (max_retries > 0), flags LIKE '!%' AS f
   FROM crdb_internal.node_statement_statistics