All we need is an easy explanation of the problem, so here it is.
What I have:
Database: PostgreSQL 9.3
Table T,
- Structure: 10 integers/bools and 1 text field
- Size: Table 89 GB / Toast 1046 GB
- Usage: about 10 inserts / minute
- Other: reltuples 59913608 / relpages 11681783
Running cascading replication: Master -> Slave 1 -> Slave 2
- Replication Master -> Slave 1 is quite fast, a good channel.
- Replication Slave 1 -> Slave 2 is slow, cross-continent, about 10 Mbit/s.
This is a live, used database with about 1.5TB more data in it.
What’s needed to be done:
- Drop all data to start with a fresh setup (to do constant cleanups and not allow it to grow this big).
Question:
What would be the most efficient way to achieve this:
- without causing huge lags between Master and Slave 1
- without causing Slave 2 to get irreversibly lagged to a state where catching up is not possible
As I see it:
- Safe way – do a copy, swap places, DELETE data constantly watching lag
- Other way – do a copy, swap places, DROP table – but this would cause enormous amounts of data at once and Slave 2 would get lost?
How to solve :
I know you bored from this bug, So we are here to help you! Take a deep breath and look at the explanation of your problem. We have many solutions to this problem, But we recommend you to use the first method because it is tested & true method that will 100% work for you.
Method 1
DROP TABLE sends very little information over the WAL stream, and the information it does send is independent of how many rows the table has in it.
Note: Use and implement method 1 because this method fully tested our system.
Thank you 🙂
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