@clickup/pg-sharding: micro-shards support for PostgreSQL

Each micro-shard is a PG schema with numeric suffix. Micro-shards have the same set of tables with same names; it's up to the higher-level tools to keep the schemas of all those tables in sync (e.g. see pg-mig tool).

Micro-shards can be moved from one PG master to another. There is no need to stop writes while moving micro-shards: the tool uses PG logical replication to stream each micro-shard table's data, and in the very end, acquires a quick exclusive lock to finalize the move.

 pg-sharding move
   --shard=N --from=DSN --to=DSN
   [--activate-on-destination]
   [--deactivate-script='SQL $1 SQL']

Each micro-shard can either be "active" or "inactive".

The library exposes low-level API for other higher-level tools as PG functions:

• sharding_list_active_shards(): returns the list of "active" shards
• sharding_ensure_exist(): allocates a new range micro-shard
• sharding_ensure_active(): activates a range of micro-shards
• sharding_ensure_inactive(): deactivates a range of micro-shards
• sharding_ensure_absent(): drops a range of micro-shards
• sharding_do_on_each(): a helper function to run an SQL query on all shards
• sharding_debug_fdw_create(): creates "debug foreign shards schemas" for each host in the list.
• sharding_debug_fds_drop(): drops all debug foreign shards schemas previously created.
• sharding_debug_views_create(): creates "debug views" for tables in all micro-shards which unions SELECTs from the same-named tables in all shards (not used in production, only for debugging purposes)
• sharding_debug_views_drop(): drops all of the debug views