PostgreSQL Really Slow During Backups

These are my notes from debugging a website problem caused by backing up the underlying database. Symptom: When backing up the database, the website is very sluggish The old backup technique amounted to

pg_dump database > file.sql \
&& rysnc file.sql remote:file.sql

I removed the rsync component and the symptom persisted. Obviously that wasn't the cause. Based on a hint in the PostgreSQL mailing list, I reduced the total IO load by completely eliminating writes with

pg_dump database > /dev/null

That fixed the problem but unfortunately it makes a lousy backup strategy. By compressing the SQL before it hits the disk, I was able to reduce the total IO load and the symptom went away. The final backup incantation amounts to

pg_dump database | gzip --rsyncable > file.sql.gz \
&& rysnc file.sql.gz remote:file.sql.gz