Slow log parse performance improvement for splitByColon

[yibin87]

Enhancement

Do cpu profile for query like:

SELECT
  Digest,
  Query,
  Conn_ID,
  (UNIX_TIMESTAMP(Time) + 0E0) AS timestamp,
  Query_time,
  Mem_max,
  Process_keys
FROM
  `INFORMATION_SCHEMA`.`CLUSTER_SLOW_QUERY`
WHERE
  Time BETWEEN FROM_UNIXTIME(?)
  AND FROM_UNIXTIME(?)
ORDER BY
  Query_time DESC
LIMIT 100;

Find the splitByColon takes about 80% cpu times:

The implementation uses regexp to parse key: value strings:

tidb/pkg/executor/slow_query.go

Lines 526 to 531 in f158c65

	// kvSplitRegex: it was just for split "field: value field: value..."
	var kvSplitRegex = regexp.MustCompile(`\w+: `)
	// splitByColon split a line like "field: value field: value..."
	func splitByColon(line string) (fields []string, values []string) {
	matches := kvSplitRegex.FindAllStringIndex(line, -1)

However, in most cases, we can just go through the string, and take string before colon as key, string after colon as value, which seems can improve performance significantly.

[yibin87]

/assign @yibin87

[yibin87]

/remove-label enhancement

[ti-chi-bot]

@yibin87: The label(s) enhancement cannot be applied. These labels are supported: fuzz/sqlancer, challenge-program, compatibility-breaker, first-time-contributor, contribution, good first issue, correctness, duplicate, proposal, security, ok-to-test, needs-ok-to-test, needs-more-info, needs-cherry-pick-release-5.4, needs-cherry-pick-release-6.1, needs-cherry-pick-release-6.5, needs-cherry-pick-release-7.1, needs-cherry-pick-release-7.5, needs-cherry-pick-release-8.1, needs-cherry-pick-release-8.3, affects-5.4, affects-6.1, affects-6.5, affects-7.1, affects-7.5, affects-8.1, affects-8.3, may-affects-5.4, may-affects-6.1, may-affects-6.5, may-affects-7.1, may-affects-7.5, may-affects-8.1.

In response to this:

/remove-label enhancement

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[yibin87]

/type bug

[yibin87]

/label affects-6.5

[yibin87]

/severity major

[yibin87]

/label affects-8.1

[yibin87]

/label affects-7.5

[yibin87]

/label affects-7.1

[yibin87]

/label affects-6.1

[yibin87]

/remove-label may-affects-5.4