Support for VictoriaMetrics extensions

[vthriller]

See:

• https://github.com/VictoriaMetrics/VictoriaMetrics/wiki/MetricsQL
• https://github.com/VictoriaMetrics/VictoriaMetrics/wiki/PromQLExtensions
• https://github.com/VictoriaMetrics/metricsql
• https://play.victoriametrics.com/promql/expand-with-exprs

[vthriller]

In short, skipping all new functions that are of no interest to us:

• aggr. op limits: sum(x) by (y) limit 10
  • why not expand that to vectors as well?
• escape chars in vector and label names: foo\-bar{baz\=aa="b"}, f\x6f\x6f = foo
• intervals measured in multiples of &step=s (think grafana's $__interval): rate(metric[10i] offset 5i)
• fractional intervals: rate(node_network_receive_bytes_total[1.5m] offset 0.5d)
• non-vector offsets: sum(foo) offset 24h
  • probably best to implement as a Node::Offset
  • funny that I sometimes wish I could stick ranges in arbitrary places, not offsets: avg_over_time(rate(foo [1m]) [5m])
• negative offsets: q offset -1h
• new operators: q1 default q2, q1 if q2, q1 ifnot q2
  • how hard would it be to allow arbitrary user-supplied operators?..
  • precedence, associativity?
• trailing commas: m{foo="bar",}, f(a, b,), WITH (x=y,) x
• string literal concatenation (useful in WITH stmts): {__name__=commonPrefix+"suffix1"}
• comments: up # this is a comment

WITH templates:

# Calculate network utilization
WITH (
    maxRate = 1e9 / 8, # Gigabit network
    commonFilters = {instance=~"$node:$port",job=~"$job"},
    networkUtilization(bytesTotal, maxRate) = ru(maxRate - rate(bytesTotal{commonFilters}[5m]), maxRate)
) networkUtilization(node_network_receive_bytes_total, maxRate)

WITH (
    f(a, b) = WITH (
        f1(x) = b-x,
        f2(x) = x+x
    ) f1(a)*f2(b)
) f(foo, with(x=bar) x)

[vthriller]

funny that I sometimes wish I could stick ranges in arbitrary places

Turns out subqueries are now a thing

[vthriller]

Comments are also supported by Prometheus 2.14 (#3).

[vthriller]

It seems VM also accepts period as valid vector name character (see also #1):

• https://github.com/VictoriaMetrics/metricsql/blob/6c5bef8a3d2cf50b14061a0806035955c01f3074/lexer.go#L478-L483
• https://github.com/VictoriaMetrics/metricsql/blob/6c5bef8a3d2cf50b14061a0806035955c01f3074/lexer_test.go#L22
• https://github.com/VictoriaMetrics/metricsql/blob/6c5bef8a3d2cf50b14061a0806035955c01f3074/lexer_test.go#L52

Prometheus though still rejects foo.bar: https://github.com/prometheus/prometheus/blob/1f69c38ba4c104520732d416de2894052806cea7/promql/parser/lex.go#L756