Beyond the hype, the PostgreSQL community is aware of the lack of "batteries-included" HA. This discussion on the idea of a Built-in Raft replication mentions MongoDB as:
>> "God Send". Everything just worked. Replication was as reliable as one could imagine. It outlives several hardware incidents without manual intervention. It allowed cluster maintenance (software and hardware upgrades) without application downtime. I really dream PostgreSQL will be as reliable as MongoDB without need of external services.
Postgres violated serializability on a single node for a considerable amount of time [1] and used fsync incorrectly for 20 years [2]. I personally witnessed lost data on Postgres because of the fsync issue.
Database engineering is very hard. MongoDB has had both poor defaults as well as bugs in the past. It will certainly have durability bugs in the future, just like Postgres and all other serious databases. I'm not sure that Postgres' durability stacks up especially well with modern MongoDB.
CloudNativePG is automation around PostgreSQL, not "batteries included", and not the idea of Kubernetes where pods can die or spawn without impacting the availability. Unfortunately, naming it Cloud Native doesn't transform a monolithic database to an elastic cluster
It's largely cultural. In the SQL world, people are used to accepting the absence of real HA (resilience to failure, where transactions continue without interruption) and instead rely on fast DR (stop the service, recover, check for data loss, start the service). In practice, this means that all connections are rolled back, clients must reconnect to a replica known to be in synchronous commit, and everything restarts with a cold cache.
Yet they still call it HA because there's nothing else.
Even a planned shutdown of the primary to patch the OS results in downtime, as all connections are terminated. The situation is even worse for major database upgrades: stop the application, upgrade the database, deploy a new release of the app because some features are not compatible between versions, test, re-analyze the tables, reopen the database, and only then can users resume work.
Everything in SQL/RDBMS was thought for a single-node instance, not including replicas. It's not HA because there can be only one read-write instance at a time. They even claim to be more ACID than MongoDB, but the ACID properties are guaranteed only on a single node.
One exception is Oracle RAC, but PostgreSQL has nothing like that. Some forks, like YugabyteDB, provide real HA with most PostgreSQL features.
About the hype: many applications that run on PostgreSQL accept hours of downtime, planned or unplanned. Those who run larger, more critical applications on PostgreSQL are big companies with many expert DBAs who can handle the complexity of database automation. And use logical replication for upgrades. But no solution offers both low operational complexity and high availability that can be comparable to MongoDB
What about "cannot scale without downtime"?
While all databases can scale vertically, increasing or decreasing CPU or memory resources requires a restart, which leads to downtime. All sessions must disconnect, the system restarts, and users reconnect and execute their first queries with a cold cache. This is far from ideal, especially when workload spikes—the very situation where scaling up is needed. Cloud-native databases that promote scalability typically scale horizontally without downtime. This involves adding or removing nodes and automatically resharding data without stopping the application. Such elasticity is key to the cost efficiency in the cloud: it lets you scale resources up or down with the workload, avoiding excess provisioning.
Can you provide more details? Inserting with unique indexes do not lock the table. Case statements are ok in where clause, use expression indexes to index it
The Write-Ahead Logging (WAL) is single-threaded and maintains consistency at a specific point in time in each instance. However, there can be anomalies between two instances. This behavior is expected because the RDS Multi-AZ cluster does not wait for changes to be applied in the shared buffers. It only waits for the WAL to sync.
This is similar to the behavior of PostgreSQL when synchronous_commit is set to on. Nothing unexpected.
>> "God Send". Everything just worked. Replication was as reliable as one could imagine. It outlives several hardware incidents without manual intervention. It allowed cluster maintenance (software and hardware upgrades) without application downtime. I really dream PostgreSQL will be as reliable as MongoDB without need of external services.
https://www.postgresql.org/message-id/0e01fb4d-f8ea-4ca9-8c9...