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Locating the recovery point just before a dropped table

A common example when talking about why it's a good thing to be able to do PITR (Point In Time Recovery) is the scenario where somebody or some thing (operator or buggy application) dropped a table, and we want to do a recover to right before the table was dropped, to keep as much valid data as possible.

PostgreSQL comes with nice functionality to decide exactly what point to perform a recovery to, which can be specified at millisecond granularity, or that of an individual transaction. But what if we don't know exactly when the table was dropped? (Exactly being at the level of specific transaction or at least millisecond).

On way to handle that is to "step forward" through the log one transaction at a time until the table is gone. This is obviously very time-consuming.

Assuming that DROP TABLE is not something we do very frequently in our system, we can also use the pg_xlogdump tool to help us find the exact spot to perform the recovery to, in much less time. Unfortunately, the dropping of temporary tables (implicit or explicit) is included in this, so if your application uses a lot of temporary tables this approach will not work out of the box. But for applications without them, it can save a lot of time.

Let's show an example. This assumes you have already set up the system for log archiving, you have a base backup that you have restored, and you have a log archive.

The first thing we do is try to determine the point where a DROP TABLE happened. We can do this by scanning for entries where rows have been deleted from the pg_class table, as this will always happen as part of the drop.

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I speak at and organize conferences around Open Source in general and PostgreSQL in particular.

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PGConf.EU 2024
Oct 22-25, 2024
Athens, Greece
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Mar 18, 2025
Copenhagen, Denmark

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PGConf NYC 2024
Sep 30-Oct 2, 2024
New York, USA
PGDay UK 2024
Sep 11, 2024
London, UK
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May 28-31, 2024
Vancouver, Canada
PGDay Chicago 2024
Apr 26, 2024
Chicago, USA
SCaLE 2024
Mar 14-17, 2024
Pasadena, USA
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