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 1. Hironobu SUZUKI @ InterDB

 * * The Internals of PostgreSQL





THE INTERNALS OF POSTGRESQL

PostgreSQL is a well-designed, open-source multi-purpose relational database
system which is widely used throughout the world.

It is one huge system with the integrated subsystems, each of which has a
particular complex feature and works cooperatively with each other. Although
understanding of the internal mechanism is crucial for both administration and
integration using PostgreSQL, its hugeness and complexity make it difficult.

The main purposes of this document are to explain how each subsystem works, and
to provide the whole picture of PostgreSQL.

This document covers versions 17 and earlier.

Some academic papers have referred to this document. The Chinese version of this
document was published in June 2019.

Contents
 * Chapter 1. Database Cluster, Databases and Tables
 * Chapter 2. Process and Memory Architecture
 * Chapter 3. Query Processing
 * Chapter 4. Foreign Data Wrappers (FDW)
 * Chapter 5. Concurrency Control
 * Chapter 6. VACUUM Processing
 * Chapter 7. Heap Only Tuple (HOT) and Index-Only Scans
 * Chapter 8. Buffer Manager
 * Chapter 9. Write Ahead Logging (WAL)
 * Chapter 10. Online Backup and Point-In-Time Recovery (PITR)
 * Chapter 11. Streaming Replication
   

Change History (since 3rd June, 2018)

DateDescription 28.Oct.2024 Added the descriptions of Incremental Backup: 9.6.2.
WAL Summarizer Process, 10.1.3. pg_basebackup and 10.5. Incremental Backup.
04.Jan.2024 Changed framework from Cascade to Relearn. 11.Sep.2023 Updated
Section 8.2.2 and Section 8.3.2. 02.Aug.2023 Fixed bug in Section 5.9.
CheckTargetForConflictsIn -> CheckForSerializableConflictIn
CheckTargetForConflictsOut -> CheckForSerializableConflictOut 02.Aug.2023 Added
Section 6.5.1 and Section 6.5.2. 02.May.2023 Splitted Chapter 3 in three files
since this part was too long. 24.Feb.2023 Removed "9.9.3. WAL Segment Management
in Version 9.4 or Earlier" in Section 9.9. 12.Jan.2023 Changed
txid_current_snapshot() to pg_current_snapshot() in Section 5.5. 22.Oct.2022
Added "archive_library" in Section 9.10. 22.Oct.2022 Updated function
names:pg_backup_start and pg_backup_stop in Chapter 10. 02.Jan.2022 Added "WAL,
Backup, and Replication" in Section 9.1.3. 12.Nov.2021 Changed the description
in the preface of Chapter 5.
 * Concurrency Control is a mechanism that maintains consistency atomicity and
   isolation,...

25.Mar.2021 Added a command to delete archiving logs in Section 9.10.
28.Jun.2020 Changed the color scheme of the all figures. 19.Jun.2020 Added
Section 3.5.3.3. 06.Jun.2020 Updated the table 4.1 in Section 4.2. Added
"PARALLEL option" in Section 6.1. Added the description about the "cleaning up
indexes" phase in Section 6.1. 04.Jun.2020 Added a description related to
recovery.conf in Section 10.2. 27.Mar.2019 Added "Indexes Internals" in Section
1.4.2. 15.Dec.2018 Fixed Section 3.3.2.1.
 * Based on the cheapest access path obtained here, a query tree a plan tree is
   generated.

10.Oct.2018 Improved Section 8.1.2. 01.Oct.2018 Fixed Section 3.3.2.2.
 * (3) Create a path, estimate the cost of the sequential scan and add the path
   to the indexlist pathlist of the RelOptInfo.

24.Aug.2018 Added Section 4.1. 13.Aug.2018 Changed in Section 9.7. 13.Aug.2018
Added "How to Maintain AUTOVACUUM" in Section 6.5. 03.Aug.2018 Added "Why the
checkpointer was separated from the background writer?" in Section 8.6.
3.Jun.2018 Updated for Version 11.
 1. Updated Section 6.1.1.
 2. Added "WAL segment file size" in Section 9.2.
 3. Added "Removal of prior checkpoint in PostgreSQL 11" in Section 9.7.2.
 4. Updated Section 9.9.2.
 5. Updated Section 10.1.1.

AUTHOR

HIRONOBU SUZUKI

I am a software programmer/engineer, the author of:

 * The Internals of PostgreSQL
 * The Engineer’s Guide To Deep Learning
 * pg_plan_inspector
 * pg_tuner

I graduated from graduate school in information engineering (M.S. in Information
Engineering), have worked for several companies as a software developer and
technical manager/director. I published seven books in the fields of database
and system integration (4 PostgreSQL books and 3 MySQL books). In June 2019, the
Chinese book of this document was published.

As a director of the Japan PostgreSQL Users Group (2010-2016), I organized the
largest (non-commercial) technical seminar/lecture on PostgreSQL in Japan for
more than six years, and also served as the program committee chair of the Japan
PostgreSQL Conference in 2013 and as a member in 2008 and 2009.

In June 2022, my interview article was published in “PostgreSQL person of the
week”.

Cuando era joven, vivió en Sudamérica por unos años. Recientemente, a veces
vuelve a allí.

I am looking for a new job, applying ML and AI technologies to DBMS.

      Blog

CONTACT

Please read the following FAQ before sending messages.

FAQ

Since publishing my content, I’ve been fortunate to receive a lot of positive
feedback, which is truly gratifying. However, unfortunately, I’ve encountered
individuals in the past who tried to misuse my content for self-promotion 1.

These experiences have shaped the approach I’ve outlined below.

 1. Who can use this document freely?
    If you are a teacher or a student belonging to an educational organization,
    you can freely use this document and figures in your study. Anyone can use
    this document and figures with noncommercial meetings and lectures, if you
    state the link to this site and the copyright; otherwise, contact me.
 2. Is it available for commercial contents?
    This content can be used under two options:
    * Revenue Share: You can leverage this content after a revenue share
      agreement is signed. Under this agreement, you’ll share 20% of the sales
      generated from using this content.
    * Full Buyout: In very rare cases, I consider requests for full commercial
      use of all content on this site. For a complete buyout of all content
      rights, the cost is €5,000,000.
 3. Does the author need any help to write?
    No. I am writing for my own enjoyment. Even if you send me your article, I
    will never include it in my document.
 4. Why doesn’t the author use the GitBook or other e-book formats/sites?
    I am using the best tools I need and I will decide what I use. I am always
    trying a lot of tools for better explanations.
    Simply put, this document is optimized to read on html file and it is hard
    to convert to other formats.
    I do not have any plan to make PDF version and Smartphone versions because
    of same reason.
 5. Why doesn’t the author use RSS to notify the update?
    I keep my domain and my server to provide my document; you can read when you
    want to read. What do you want more?
 6. Why doesn’t the author waive the copyright of this document or use the
    creative commons license?
    I’d like to ask you what problems you have by that I keep on having the
    copyright of my document.

--------------------------------------------------------------------------------

 1. See the source code. ↩︎

After reading, send a message to my twitter in public.

or   /    

If you use email, please provide at least two SNS addresses (e.g. LinkedIn,
Twitter) for verification purposes. Due to the XZ backdoor incident, I no longer
accept contact from anonymous individuals.

COPYRIGHT

© Copyright ALL Right Reserved, Hironobu SUZUKI.

For any inquiries regarding the use of this document or any of its figures,
please contact me.

Exception Educational institutions can use this document freely.


The Internals of PostgreSQL
Search

 * Home

 * 1. DB Cluster, DB and Tables
   * 1.1. Logical Structure of DB Cluster
   * 1.2. Physical Structure of DB Cluster
   * 1.3. Internal Layout of Heap Table File
   * 1.4. Writing and Reading Tuples
 * 2. Process and Memory Arch.
   * 2.1. Process Architecture
   * 2.2. Memory Architecture
 * 3. Query Processing
   * 3.1. Overview
   * 3.2. Cost Estimation in Single-Table Query
   * 3.3. Creating the Plan Tree of a Single-Table Query
   * 3.4. How the Executor Performs
   * 3.5. Join Operations
     * 3.5.1. Nested Loop Join
     * 3.5.2. Merge Join
     * 3.5.3. Hash Join
     * 3.5.4. Join Access Paths and Join Nodes
   * 3.6. Creating the Plan Tree of Multiple-Table Query
 * 4. Foreign Data Wrappers (FDW)
   * 4.1. Overview
   * 4.2. postgres_fdw
 * 5. Concurrency Control
   * 5.1 Transaction ID
   * 5.2 Tuple Structure
   * 5.3. Inserting, Deleting and Updating Tuples
   * 5.4. Commit Log (clog)
   * 5.5. Transaction Snapshot
   * 5.6. Visibility Check Rules
   * 5.7. Visibility Check
   * 5.8. Preventing Lost Updates
   * 5.9. Serializable Snapshot Isolation
   * 5.10. Maintenance Processes
 * 6. VACUUM Processing
   * 6.1. Outline of Concurrent VACUUM
   * 6.2. Visibility Map
   * 6.3. Freeze Processing
   * 6.4. Removing Unnecessary Clog Files
   * 6.5. Autovacuum Daemon
   * 6.6. Full VACUUM
 * 7. HOT and Index-Only Scans
   * 7.1. Heap Only Tuple (HOT)
   * 7.2. Index-Only Scans
 * 8. Buffer Manager
   * 8.1. Overview
   * 8.2. Buffer Manager Structure
   * 8.3. Buffer Manager Locks
   * 8.4. How the Buffer Manager Works
   * 8.5. Ring Buffer
   * 8.6. Flushing Dirty Pages
 * 9. Write Ahead Logging (WAL)
   * 9.1. Overview
   * 9.2. Transaction Log and WAL Segment Files
   * 9.3. Internal Layout of WAL Segment
   * 9.4. Internal Layout of XLOG Record
   * 9.5. Writing of XLOG Records
   * 9.6. WAL related processes
   * 9.7. Checkpoint Processing
   * 9.8. Database Recovery
   * 9.9. WAL Segment Files Management
   * 9.10. Continuous Archiving and Archive Logs
 * 10. Online Backup and PITR
   * 10.1. Base Backup
   * 10.2. How Point-in-Time Recovery Works
   * 10.3. timelineId and Timeline History File
   * 10.4. Point-in-Time Recovery with Timeline History File
   * 10.5. Incremental Backup
 * 11. Streaming Replication
   * 11.1. Starting the Streaming Replication
   * 11.2. How to Conduct Streaming Replication
   * 11.3. Managing Multiple-Standby Servers
   * 11.4. Detecting Failures of Standby Servers

More
 * Personal Site
 * The Engineer's Guide To Deep Learning
 * GitHub repo



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