Class: Scryer::PerformanceRules::UnboundedTableScanRule

Inherits:
Rule
  • Object
show all
Defined in:
lib/scryer/performance_rules/unbounded_table_scan_rule.rb

Overview

Flags Model.all.each/Model.where(...).each (or .order(...).each) — chaining .each directly onto a query loads every matching row into memory at once before iterating. find_each/find_in_batches load and yield records in bounded batches instead, keeping memory flat regardless of table size. This only looks at the literal chain (Const.query.each) so it won't catch the same problem one step removed — e.g. a variable assigned from the query and iterated later (that pattern is out of scope here; see NPlusOneQueryRule, which does track simple local assignments, for a related check on what happens inside such a loop).

Constant Summary collapse

QUERY_METHODS = 
%w[all where order].freeze

Instance Attribute Summary

Attributes inherited from Rule

#file, #sexp, #source

Instance Method Summary collapse

Methods inherited from Rule

inherited, #initialize

Constructor Details

This class inherits a constructor from Scryer::Rule

Instance Method Details

#scan ⇒ Object 



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# File 'lib/scryer/performance_rules/unbounded_table_scan_rule.rb', line 20

def scan
  findings = []

  Ast.each_node(sexp) do |node|
    next unless Ast.tagged?(node, :method_add_block)

    call_node = node[1]
    receiver, method_name = Ast.call_name(call_node) || [nil, nil]
    next unless method_name == "each"
    next unless receiver
    next unless direct_query_chain?(receiver)

    line = Ast.line_of(call_node)
    findings << finding(
      line: line,
      message: "`.each` is chained directly onto a query — Active Record loads every " \
                "matching row into memory before the block runs even once, which can exhaust " \
                "memory (or just be very slow) once the table is large.",
      suggested_fix: "Use `find_each` (row-by-row, fixed batch size) or `find_in_batches` " \
                      "(access a batch `Array` at a time) instead of `.each`, e.g. " \
                      "`Model.where(...).find_each { |record| ... }` — Active Record loads and " \
                      "discards records in bounded batches instead of all at once."
    )
  end

  findings
end