# Part VII. Internals
This part contains assorted information that might be of use to PostgreSQL developers.
Table of Contents
51. Overview of PostgreSQL Internals
51.2. How Connections Are Established
51.4. The PostgreSQL Rule System
52.23. pg_foreign_data_wrapper
52.31. pg_largeobject_metadata
52.65. pg_available_extensions
52.66. pg_available_extension_versions
52.67. pg_backend_memory_contexts
52.80. pg_replication_origin_status
53.4. Streaming Replication Protocol
53.5. Logical Streaming Replication Protocol
53.8. Error and Notice Message Fields
53.9. Logical Replication Message Formats
53.10. Summary of Changes since Protocol 2.0
54. PostgreSQL Coding Conventions
54.2. Reporting Errors Within the Server
54.3. Error Message Style Guide
54.4. Miscellaneous Coding Conventions
56. Writing a Procedural Language Handler
57. Writing a Foreign Data Wrapper
57.1. Foreign Data Wrapper Functions
57.2. Foreign Data Wrapper Callback Routines
57.3. Foreign Data Wrapper Helper Functions
57.4. Foreign Data Wrapper Query Planning
57.5. Row Locking in Foreign Data Wrappers
58. Writing a Table Sampling Method
58.1. Sampling Method Support Functions
59. Writing a Custom Scan Provider
59.1. Creating Custom Scan Paths
59.2. Creating Custom Scan Plans
60.1. Query Handling as a Complex Optimization Problem
60.3. Genetic Query Optimization (GEQO) in PostgreSQL
61. Table Access Method Interface Definition
62. Index Access Method Interface Definition
62.1. Basic API Structure for Indexes
62.2. Index Access Method Functions
62.4. Index Locking Considerations
62.6. Index Cost Estimation Functions
64.2. Behavior of B-Tree Operator Classes
64.3. B-Tree Support Functions
65.2. Built-in Operator Classes
66.2. Built-in Operator Classes
67.2. Built-in Operator Classes
68.2. Built-in Operator Classes
71. System Catalog Declarations and Initial Contents
71.1. System Catalog Declaration Rules
71.2. System Catalog Initial Data
71.5. Structure of the Bootstrap BKI File
72. How the Planner Uses Statistics
72.2. Multivariate Statistics Examples
72.3. Planner Statistics and Security
73.1. Backup Manifest Top-level Object