如何使用 PostgreSQL 的“pg_restore”和零停机恢复数据？

Question

I try to restore a large table

pg_restore.exe -U postgres -d db_name --clean --if-exists --single-transaction F:\Backups\PostgreSQL\data.dump.gz

So I have a read lock for a few minutes. How to restore data with zero downtime for reading? I need only reading.

Answer 1

You would need to not do the --clean and instead do --data-only, but then do a DELETE from tablename inside the same transaction, before the COPY. I don't think there is a way to make pg_restore do this for you, but you could dump the output of pg_restore to a file and edit it, or use something like sed or perl to inject the DELETE.

This should work for table names which don't need to be quoted, and assuming none of the data being copied has first column which starts with 'COPY ':

pg_restore --data-only --single-transaction dmp.dmp -f -| perl -pe 's/^COPY ([\w.]+)/delete from $1; copy $1/' | psql -U postgres -d db_name

However, your schema changing method doesn't seem so dirty to me. It still requires a momentary access exclusive lock, so it isn't really zero downtime, but it might be unnoticable downtime if it can acquire said lock quickly enough.