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 16 and earlier.

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

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
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
  • 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) 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.


Hironobu SUZUKI

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

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.



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