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PostgreSQL actually supports sharding out of the box, it's just a matter of setting up the right table partitioning and using Foreign Data Wrapper (FDW) to forw

PostgreSQL actually supports sharding out of the box, it's just a matter of setting up the right table partitioning and using Foreign Data Wrapper (FDW) to forward queries to remote databases. I'm not sure what the post is referencing when they say that sharding requires leaving Postgres altogether.

dmix 10mo ago
This is specifically what they said about sharding > The primary rationale is that sharding existing application workloads would be highly complex and time-consuming, requiring changes to hundreds of application endpoints and potentially taking months or even years
- zozbot234 10mo ago
  I know they said that, but in fact sharding is entirely a database-level concern. The application need not be aware of it at all.
  - EB66 10mo ago
    Sharding can be made mostly transparent, but it's not purely a DB-level concern in practice. Once data is split across nodes, join patterns, cross-shard transactions, global uniqueness, certain keys hit with a lot of traffic, etc matter a lot. Even if partitioning handles routing, the application's query patterns and its consistency/latency requirements can still force application-level changes.
    - awesome_dude 10mo ago
      > Once data is split across nodes, join patterns, cross-shard transactions, global uniqueness, certain keys hit with a lot of traffic If you're having trouble there then a proxy "layer" between your application and the sharded database makes sense, meaning your application still keeps its naieve understanding of the data (as it should) and the proxy/database access layer handles that messiness... shirley
    - zozbot234 10mo ago
      > mostly transparent, but it's not purely a DB-level concern in practice ... But how would any of that change by going outside Postgres itself to begin with? That's the part that doesn't make much sense to me.
      - londons_explore 10mo ago
        When sharded, anything crossing a shard boundary becomes non-transactional. Ie. if you shard by userId, then a "share" feature which allows a user to share data with another user by having a "SharedDocuments" table cannot be consistent. That in turn means you're probably going to have to rewrite the application to handle cases like a shared document having one or other user attached to it disappear or reappear. There are loads of bugs that can happen with weak consistency like this, and at scale every very rare bug is going to happen and need dealing with.
        zozbot234 10mo ago
        > When sharded, anything crossing a shard boundary becomes non-transactional. Not necessarily? You can have two-phase commit for cross-shard writes, which ought to be rare anyway.
        londons_explore 10mo ago
        Two-phase commit provides an eventual consistency guarantee only.... Other clients (readers) have to be able to deal with inconsistencies in the meantime. Also, 2PC in postgres is incompatible with temporary tables, which rules out use with longrunning batch analysis jobs which might use temporary tables for intermediate work and then save results. Eg. "We want to send this marketing campaign to the top 10% of users" doesn't work with the naive approach.
        ants_a 10mo ago
        These are limitations in the current PostgreSQL implementation. It's quite possible to have consistent commits and snapshots across sharded databases. Hopefully some day in PostgreSQL too.
- simonw 10mo ago
  Genuinely sounds like the kind of challenge that could be solved with a swarm of Codex coding agents. I'm surprised they aren't treating this as an ideal use-case to show off their stack!
  - csto12 10mo ago
    I read your message, guessed the author, and I’m happy to announce I guessed correctly.
  - aisuxmorethanhn 10mo ago
    It wouldn’t work.
  - Ozzie_osman 10mo ago
    Getting the sharing in-place, yes, but maintaining it operationally would still be a headache. Things like schema migrations across shards, resharding, and even observability.
  - gloflo 10mo ago
    Oh snap! Maybe it's all a great deception for making money?
- manquer 10mo ago
  > potentially taking months or even years On one hand OAI sell coding agents and constantly hype how easy it will replace developers and most of the code written is by agents, on the other hand they claim it will take years to refactor Both cannot be true at the same time.
mkleczek 10mo ago
Shameless plug: https://github.com/mkleczek/pgwrh https://github.com/mkleczek/pgwrh automates it quite a bit.

dmix 10mo ago

This is specifically what they said about sharding > The primary rationale is that sharding existing application workloads would be highly complex and time-consuming, requiring changes to hundreds of application endpoints and potentially taking months or even years

zozbot234 10mo ago
I know they said that, but in fact sharding is entirely a database-level concern. The application need not be aware of it at all.
- EB66 10mo ago
  Sharding can be made mostly transparent, but it's not purely a DB-level concern in practice. Once data is split across nodes, join patterns, cross-shard transactions, global uniqueness, certain keys hit with a lot of traffic, etc matter a lot. Even if partitioning handles routing, the application's query patterns and its consistency/latency requirements can still force application-level changes.
  - awesome_dude 10mo ago
    > Once data is split across nodes, join patterns, cross-shard transactions, global uniqueness, certain keys hit with a lot of traffic If you're having trouble there then a proxy "layer" between your application and the sharded database makes sense, meaning your application still keeps its naieve understanding of the data (as it should) and the proxy/database access layer handles that messiness... shirley
  - zozbot234 10mo ago
    > mostly transparent, but it's not purely a DB-level concern in practice ... But how would any of that change by going outside Postgres itself to begin with? That's the part that doesn't make much sense to me.
    - londons_explore 10mo ago
      When sharded, anything crossing a shard boundary becomes non-transactional. Ie. if you shard by userId, then a "share" feature which allows a user to share data with another user by having a "SharedDocuments" table cannot be consistent. That in turn means you're probably going to have to rewrite the application to handle cases like a shared document having one or other user attached to it disappear or reappear. There are loads of bugs that can happen with weak consistency like this, and at scale every very rare bug is going to happen and need dealing with.
      - zozbot234 10mo ago
        > When sharded, anything crossing a shard boundary becomes non-transactional. Not necessarily? You can have two-phase commit for cross-shard writes, which ought to be rare anyway.
        londons_explore 10mo ago
        Two-phase commit provides an eventual consistency guarantee only.... Other clients (readers) have to be able to deal with inconsistencies in the meantime. Also, 2PC in postgres is incompatible with temporary tables, which rules out use with longrunning batch analysis jobs which might use temporary tables for intermediate work and then save results. Eg. "We want to send this marketing campaign to the top 10% of users" doesn't work with the naive approach.
        ants_a 10mo ago
        These are limitations in the current PostgreSQL implementation. It's quite possible to have consistent commits and snapshots across sharded databases. Hopefully some day in PostgreSQL too.
simonw 10mo ago
Genuinely sounds like the kind of challenge that could be solved with a swarm of Codex coding agents. I'm surprised they aren't treating this as an ideal use-case to show off their stack!
- csto12 10mo ago
  I read your message, guessed the author, and I’m happy to announce I guessed correctly.
- aisuxmorethanhn 10mo ago
  It wouldn’t work.
- Ozzie_osman 10mo ago
  Getting the sharing in-place, yes, but maintaining it operationally would still be a headache. Things like schema migrations across shards, resharding, and even observability.
- gloflo 10mo ago
  Oh snap! Maybe it's all a great deception for making money?
manquer 10mo ago
> potentially taking months or even years On one hand OAI sell coding agents and constantly hype how easy it will replace developers and most of the code written is by agents, on the other hand they claim it will take years to refactor Both cannot be true at the same time.

mkleczek 10mo ago

Shameless plug: https://github.com/mkleczek/pgwrh https://github.com/mkleczek/pgwrh automates it quite a bit.