Besides what's already mentioned by siblings:
- Forwards (and usually also backwards) compatible disk format, meaning version updates don't require more than a few minutes of downtime. On large datasets, postgresql can require days or weeks.
- Replication works across version differences, making upgrades without any downtime at all easier.
- No need for a vacuum process that can run into trouble with a sustained high write load.
- Page-level compression, reducing storage needs for some types of data quite a bit.
- Clustered primary keys. Without these, some types of queries can become rather slow when your table doesn't fit in memory. (Example: a chat log containing many billions of messages, which you're querying by conversion-id.)
- xtrabackup (innobackupex) is awesome.
- Forwards (and usually also backwards) compatible disk format, meaning version updates don't require more than a few minutes of downtime. On large datasets, postgresql can require days or weeks.
- Replication works across version differences, making upgrades without any downtime at all easier.
- No need for a vacuum process that can run into trouble with a sustained high write load.
- Page-level compression, reducing storage needs for some types of data quite a bit.
- Clustered primary keys. Without these, some types of queries can become rather slow when your table doesn't fit in memory. (Example: a chat log containing many billions of messages, which you're querying by conversion-id.)
- xtrabackup (innobackupex) is awesome.