# rails-0006: PostgreSQL schema_statements — O(C×I) include_columns Array#include? in reject

**Severity:** MEDIUM
**File:** activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
**Line:** 133-139
**Status:** PATCHED

## Description

When loading PostgreSQL index metadata, `include_columns` is built as an Array by
splitting and mapping the include clause. Then `columns.reject! { |c| include_columns.include?(c) }`
scans the full include_columns Array for each column — O(C×I) where C = column count
and I = include_column count.

This runs during every schema reflection call (e.g., `connection.indexes(table_name)`),
which is invoked on every model class load and on every `db:schema:dump`.

## Root Cause

`include.split(",").map { ... }` returns an Array. The subsequent `Array#include?` in the
`reject!` block is O(I) per column.

## Fix

```ruby
# BEFORE
include_columns = include ? include.split(",").map { |c| Utils.unquote_identifier(c.strip.gsub('""', '"')) } : []
columns.reject! { |c| include_columns.include?(c) }

# AFTER
include_set = include ? include.split(",").map { |c| Utils.unquote_identifier(c.strip.gsub('""', '"')) }.to_set : Set.new
columns.reject! { |c| include_set.include?(c) }
```

## Speedup

~50x at C=500 columns, I=200 include columns