PromQL Error Recovery Guide

When validate_promql.py or Cloud Monitoring query execution reports a syntax or type error, use this reference to diagnose and fix the query before repeating the validation loop.

Table of Contents

• Common Error Diagnoses & Solutions (~Line 24)
  • Range Vector vs. Instant Vector Type Mismatch (~Line 26)
  • Invalid Grouping Clause Placement (by / without) (~Line 45)
  • Histogram Quantile Bucket & Label Mismatch (~Line 63)
  • Vector Matching & Binary Operator Collision (~Line 81)
  • Unquoted Literals & Equality Operators (~Line 99)
  • Trailing Comments or Multiline Collisions (~Line 115)

Common Error Diagnoses & Solutions

Range Vector vs. Instant Vector Type Mismatch

• Error: expected type range vector in call to function "rate", got instant vector (or irate, increase).

• Cause: Calling rate() without a time duration window (such as rate(metric)), or placing an aggregation operator inside the rate (such as rate(sum(metric)[5m])). In PromQL, functions like sum() or avg() return an instant vector, which cannot be passed to rate().

• Fix: Ensure rate(), irate(), and increase() wrap the raw metric with a duration window, and place aggregation operators on the outside:

  # Wrong
  rate(sum(compute_googleapis_com:instance_network_sent_bytes_count)[5m])
  
  # Correct
  sum(rate(compute_googleapis_com:instance_network_sent_bytes_count[5m]))
  

Invalid Grouping Clause Placement (by / without)

• Error: syntax error: unexpected BY or invalid label grouping.

• Cause: Attaching a grouping clause directly to a raw metric selector or rate function. In PromQL, by (...) and without (...) can only attach to aggregation operators (sum, avg, min, max, count, topk, bottomk, quantile, stddev, stdvar).

• Fix: Move the grouping clause to attach directly to the aggregation operator:

  # Wrong
  rate(bigtable_googleapis_com:server_read_count[5m]) by (table_id)
  
  # Correct
  sum(rate(bigtable_googleapis_com:server_read_count[5m])) by (table_id)
  

Histogram Quantile Bucket & Label Mismatch

• Error: histogram_quantile requires a "le" label in the input vector or empty/NaN distribution calculation.

• Cause: Using histogram_quantile() without grouping by the le (less-than-or-equal) bucket boundary label, or forgetting to append the _bucket suffix to the distribution metric name.

• Fix: Append _bucket to the metric name and ensure le is included in the by (...) clause alongside any target instance labels:

  # Wrong
  histogram_quantile(0.95, sum(rate(cloudfunctions_googleapis_com:function_execution_times[5m])) by (function_name))
  
  # Correct
  histogram_quantile(0.95, sum(rate(cloudfunctions_googleapis_com:function_execution_times_bucket[5m])) by (le, function_name))
  

Vector Matching & Binary Operator Collision

• Error: multiple matches for labels: many-to-one matching must be explicit (group_left/group_right).

• Cause: Performing arithmetic between two different time series (for example, dividing the error count by the total request count) when the label sets do not match 1-to-1 across both sides of the operator.

• Fix: Use ignoring(...) or on(...) to specify the exact label subset for matching, and append group_left or group_right for many-to-one or one-to-many ratios:

  # Correcting a many-to-one ratio
  sum(rate(error_metric[5m])) by (method, service)
    / on (service) group_left(method)
    sum(rate(total_requests[5m])) by (service)
  

Unquoted Literals & Equality Operators

• Error: unexpected identifier or invalid label matcher.

• Cause: Using unquoted strings in label selectors, or using a single = instead of == for boolean comparisons outside label selectors.

• Fix: Quote all string literals inside label matchers, and use double equals == for value comparisons:

  # Wrong
  http_requests_total{environment=prod} = 0
  
  # Correct
  http_requests_total{environment="prod"} == 0
  

Trailing Comments or Multiline Collisions

• Error: Silently ignored filters, syntax errors at the end of the query, or unexpected end of input.
• Cause: Including comments (# ...) or line breaks when transmitting queries to single-line Cloud Monitoring translation APIs. Cloud Monitoring's parser collapses whitespace and treats everything after # on the same line as a comment.
• Fix: Strip all markdown formatting, line breaks, and # comments before passing the string to validation or execution.