Class: PgCanary::Rules::UnindexedOrderByWithLimit

Inherits:
Base
  • Object
show all
Includes:
IndexPredicates
Defined in:
lib/pg_canary/rules/definitions/unindexed_order_by_with_limit.rb

Overview

ORDER BY x LIMIT n without an index led by x forces a full sort before the limit can apply. Size-dependent, so disabled by default.

Constant Summary

Constants included from IndexPredicates

IndexPredicates::TRGM_ACCESS_METHODS

Instance Method Summary collapse

Methods inherited from Base

all, check, default_enabled, enabled?, #initialize, option, options, rule_name

Constructor Details

This class inherits a constructor from PgCanary::Rules::Base

Instance Method Details

#check ⇒ Object 



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# File 'lib/pg_canary/rules/definitions/unindexed_order_by_with_limit.rb', line 15

def check
  detections = []
  each_scope do |scope|
    next unless scope.limited?

    sort_by = scope.sort_items.first
    next unless sort_by

    column_ref = sort_by.node&.unwrap
    next unless column_ref.is_a?(PgQuery::ColumnRef)

    table, column = scope.resolve(column_ref)
    next unless table && column
    next unless applicable_table?(table)
    next if index_leading_with?(table, column)

    detections << detection(
      table: table,
      columns: column,
      message: "ORDER BY #{column} LIMIT sorts every row before the limit can apply " \
               "(no index on #{table} leads with #{column}).",
      suggestion: <<~SUGGESTION.chomp
        Consider indexing the sort key:
          CREATE INDEX index_#{table}_on_#{column} ON #{table} (#{column});
      SUGGESTION
    )
  end
  detections
end