# pg_dirtyread **Repository Path**: lucky912_admin/pg_dirtyread ## Basic Information - **Project Name**: pg_dirtyread - **Description**: No description available - **Primary Language**: Unknown - **License**: Not specified - **Default Branch**: master - **Homepage**: None - **GVP Project**: No ## Statistics - **Stars**: 0 - **Forks**: 0 - **Created**: 2020-10-20 - **Last Updated**: 2024-11-26 ## Categories & Tags **Categories**: Uncategorized **Tags**: None ## README pg_dirtyread ============ The pg_dirtyread extension provides the ability to read dead but unvacuumed rows from a relation. Supports PostgreSQL 9.2 and later. (On 9.2, at least 9.2.9 is required.) Building -------- To build pg_dirtyread, just do this: make make install If you encounter an error such as: make: pg_config: Command not found Be sure that you have `pg_config` installed and in your path. If you used a package management system such as RPM to install PostgreSQL, be sure that the `-devel` package is also installed. If necessary tell the build process where to find it: make PG_CONFIG=/path/to/pg_config make install PG_CONFIG=/path/to/pg_config Loading and Using ------- Once pg_dirtyread is built and installed, you can add it to a database. Loading pg_dirtyread is as simple as connecting to a database as a super user and running: ```sql CREATE EXTENSION pg_dirtyread; SELECT * FROM pg_dirtyread('tablename') AS t(col1 type1, col2 type2, ...); ``` The `pg_dirtyread()` function returns RECORD, therefore it is necessary to attach a table alias clause that describes the table schema. Columns are matched by name, so it is possible to omit some columns in the alias, or rearrange columns. Example: ```sql CREATE EXTENSION pg_dirtyread; -- Create table and disable autovacuum CREATE TABLE foo (bar bigint, baz text); ALTER TABLE foo SET ( autovacuum_enabled = false, toast.autovacuum_enabled = false ); INSERT INTO foo VALUES (1, 'Test'), (2, 'New Test'); DELETE FROM foo WHERE bar = 1; SELECT * FROM pg_dirtyread('foo') as t(bar bigint, baz text); bar │ baz ─────┼────────── 1 │ Test 2 │ New Test ``` Dropped Columns --------------- The content of dropped columns can be retrieved as long as the table has not been rewritten (e.g. via `VACUUM FULL` or `CLUSTER`). Use `dropped_N` to access the Nth column, counting from 1. PostgreSQL deletes the type information of the original column, so only a few sanity checks can be done if the correct type was specified in the table alias; checked are type length, type alignment, type modifier, and pass-by-value. ```sql CREATE TABLE ab(a text, b text); INSERT INTO ab VALUES ('Hello', 'World'); ALTER TABLE ab DROP COLUMN b; DELETE FROM ab; SELECT * FROM pg_dirtyread('ab') ab(a text, dropped_2 text); a │ dropped_2 ───────┼─────────── Hello │ World ``` System Columns -------------- System columns such as `xmax` and `ctid` can be retrieved by including them in the table alias attached to the `pg_dirtyread()` call. A special column `dead` of type boolean is available to report dead rows (as by `HeapTupleIsSurelyDead`). The `dead` column is not usable during recovery, i.e. most notably not on standby servers. The `oid` column is only available in PostgreSQL version 11 and earlier. ```sql SELECT * FROM pg_dirtyread('foo') AS t(tableoid oid, ctid tid, xmin xid, xmax xid, cmin cid, cmax cid, dead boolean, bar bigint, baz text); tableoid │ ctid │ xmin │ xmax │ cmin │ cmax │ dead │ bar │ baz ──────────┼───────┼──────┼──────┼──────┼──────┼──────┼─────┼─────────────────── 41823 │ (0,1) │ 1484 │ 1485 │ 0 │ 0 │ t │ 1 │ Delete 41823 │ (0,2) │ 1484 │ 0 │ 0 │ 0 │ f │ 2 │ Insert 41823 │ (0,3) │ 1484 │ 1486 │ 0 │ 0 │ t │ 3 │ Update 41823 │ (0,4) │ 1484 │ 1488 │ 0 │ 0 │ f │ 4 │ Not deleted 41823 │ (0,5) │ 1484 │ 1489 │ 1 │ 1 │ f │ 5 │ Not updated 41823 │ (0,6) │ 1486 │ 0 │ 0 │ 0 │ f │ 3 │ Updated 41823 │ (0,7) │ 1489 │ 0 │ 1 │ 1 │ t │ 5 │ Not quite updated 41823 │ (0,8) │ 1490 │ 0 │ 2 │ 2 │ t │ 6 │ Not inserted ``` Authors ------- pg_dirtyread 1.0 was written by Phil Sorber in 2012. Christoph Berg added the ability to retrieve system columns in version 1.1, released 2017, and took over further maintenance. License ------- Copyright (c) 1996-2022, PostgreSQL Global Development Group Copyright (c) 2012, OmniTI Computer Consulting, Inc. Portions Copyright (c) 1994, The Regents of the University of California All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: * Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. * Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. * Neither the name OmniTI Computer Consulting, Inc. nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.