Recover Lost PostgreSQL Data with pg_recovery: Step‑by‑Step Guide

Quickly restoring lost data is a critical requirement for any database, and PostgreSQL offers several official tools; the open‑source community also provides useful alternatives.

What is pg_recovery?

pg_recovery is a PostgreSQL data‑recovery extension that can restore changes caused by COMMIT, DELETE, UPDATE, ROLLBACK, and DROP COLUMN operations and returns the recovered rows as a table. The source code is available at https://github.com/radondb/pg_recovery .

Quick Installation

$ make PG_CONFIG=/home/lzzhang/PG/postgresql/base/bin/pg_config
gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -Wno-stringop-truncation -g -g -O0 -fPIC -I. -I./ -I/home/lzzhang/PG/postgresql/base/include/server -I/home/lzzhang/PG/postgresql/base/include/internal  -D_GNU_SOURCE   -c -o pg_recovery.o pg_recovery.c
gcc -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Werror=vla -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fexcess-precision=standard -Wno-format-truncation -Wno-stringop-truncation -g -g -O0 -fPIC -shared -o pg_recovery.so pg_recovery.o -L/home/lzzhang/PG/postgresql/base/lib    -Wl,--as-needed -Wl,-rpath,'/home/lzzhang/PG/postgresql/base/lib',--enable-new-dtags

$ make install PG_CONFIG=/home/lzzhang/PG/postgresql/base/bin/pg_config
/usr/bin/mkdir -p '/home/lzzhang/PG/postgresql/base/lib'
/usr/bin/mkdir -p '/home/lzzhang/PG/postgresql/base/share/extension'
/usr/bin/install -c -m 755  pg_recovery.so '/home/lzzhang/PG/postgresql/base/lib/pg_recovery.so'
/usr/bin/install -c -m 644 .//pg_recovery.control '/home/lzzhang/PG/postgresql/base/share/extension/'
/usr/bin/install -c -m 644 .//pg_recovery--1.0.sql  '/home/lzzhang/PG/postgresql/base/share/extension/'

After installing the shared library, create the extension in the database:

$ create extension pg_recovery ;
CREATE EXTENSION

Data Recovery Demonstration

Prepare Initial Data

$ create table lzzhang(id int, dp int);
CREATE TABLE
$ insert into lzzhang values(1, 1);
INSERT 0 1
$ insert into lzzhang values(2, 2);
INSERT 0 1

Recover UPDATE Data

$ update lzzhang set id=3, dp=3;
UPDATE 2
lzzhang=# select * from pg_recovery('lzzhang') as (id int, dp int);
 id | dp 
----+----
  1 |  1
  2 |  2
(2 rows)

$ select * from lzzhang;
 id | dp 
----+----
  3 |  3
  3 |  3
(2 rows)

Recover DELETE Data

$ delete from lzzhang;
DELETE 2
lzzhang=# select * from lzzhang;
 id | dp 
----+----
(0 rows)

$ select * from pg_recovery('lzzhang') as (id int, dp int);
 id | dp 
----+----
  1 |  1
  2 |  2
  3 |  3
  3 |  3
(4 rows)

Recover ROLLBACK Data

$ begin ;
BEGIN
$ insert into lzzhang values(4, 4);
INSERT 0 1
$ rollback ;
ROLLBACK
$ select * from lzzhang;
 id | dp 
----+----
(0 rows)

$ select * from pg_recovery('lzzhang') as (id int, dp int);
 id | dp 
----+----
  1 |  1
  2 |  2
  3 |  3
  3 |  3
  4 |  4
(5 rows)

Recover DROP COLUMN Data

$ alter table lzzhang drop column dp;
ALTER TABLE
$ select attnum from pg_attribute, pg_class where attrelid = pg_class.oid and pg_class.relname='lzzhang' and attname ~ 'dropped';
 attnum 
--------
      2
(1 row)

$ select * from lzzhang;
 id 
----
(0 rows)

$ select * from pg_recovery('lzzhang') as (id int, dropped_attnum_2 int);
 id | dropped_attnum_2 
----+------------------
  1 |                1
  2 |                2
  3 |                3
  3 |                3
  4 |                4
(5 rows)

Show All Recovered Data

$ insert into lzzhang values(5);
INSERT 0 1
$ select * from lzzhang;
 id 
----
  5
(1 row)

$ select * from pg_recovery('lzzhang', recoveryrow => false) as (id int, recoveryrow bool);
 id | recoveryrow 
----+-------------
  1 | t
  2 | t
  3 | t
  3 | t
  4 | t
  5 | f
(6 rows)

Important Notes

Supported PostgreSQL versions : pg_recovery works with PostgreSQL 12, 13, and 14.

Recoverable transaction count : The number of transactions that can be recovered depends on the vacuum_defer_cleanup_age setting. Increase this parameter if you need to recover a larger volume of data.

Lock behavior : While pg_recovery is active, normal read‑locks are allowed; when it is not in use, the extension imposes no additional overhead and does not require service downtime.