[psteinroe]

Stacked on #936 → #921 → … → #881. Must merge after #881.

With nested configurations every database a configuration points at gets a connection pool and a schema snapshot, and nothing ever dropped them. Editing a nested config to point at another database, renaming a folder, or removing a workspace folder left the old pool (with its open connections) and its snapshot in memory until the server stopped. The existing idle cleanup of pools only ran when a new pool was created, and a cache hit didn't count as a use, so a pool in constant use could be evicted while an idle one stayed.

How big is a snapshot

crates/pgls_workspace/tests/snapshot_memory.rs (ignored, needs the test DB) counts the bytes a loaded Snapshot keeps allocated, with a counting global allocator:

Database	Tables	Columns	Functions	Types	Snapshot
local postgres (mostly the system catalog)	212	2,020	3,285	619	2.8 MiB
+ 500 tables × 10 columns, 200 functions, 50 views, 20 enums	758	8,055	3,444	1,751	4.7 MiB

So each database costs about 3 MiB before it has any user objects, plus a few KiB per table. That's fine for a handful of databases, but it adds up when stale ones are never dropped.

Caches and their bounds

Cache	Key	Grows with	Dropped when
ConnectionManager.pools	host, port, user, database	distinct databases in use	new: no project's root or nested settings use it (after update_settings, update_nested_settings, unregister_project_folder); unused for 5 min (fixed: hits count, the check runs at most once a minute on any use); settings fingerprint changes
connections inside a pool	—	concurrent queries	new: sqlx closes a connection idle for 5 min (idle_timeout, was sqlx's 10 min default)
ConnectionManager.failures	same	failing databases	success, settings change, new: unused
SnapshotManager.db_schemas	same	distinct databases loaded, ~3–5 MiB each	new: unused (as above); new: not used for 30 min, loaded again on the next use; invalidate_schema_cache
catalog_base, snapshot_before	—	one entry each	replaced on the next use (unchanged)
session root_files, configuration_files, real_folders	workspace folder	folders	rebuilt on every reload

Evictions are logged at debug level; a dropped pool or snapshot is created again on the next use, so results don't change.

LastUsed (an atomic timestamp) lets a cache hit under the read lock record a use.

Tests

• connection_manager: unused_connections_are_dropped, idle_pools_are_closed (incl. the once-a-minute check).
• snapshot_manager: unused_snapshots_are_dropped, idle_snapshots_are_dropped.
• pgls_workspace: the_connection_of_a_removed_configuration_is_dropped, against the test DB. A nested config that connects keeps one pool and one snapshot; moving it to another folder with the same database keeps them; removing it drops both.

Not covered

• The second pool per database from fix(workspace): don't leak transactions or session settings from executed statements #907 is in another stack. When the two meet, its map needs the same retain call in drop_unused_connections.
• During a reload, the root settings are applied before the nested ones. A database that moves from the root to a nested file in one edit is dropped and loaded again once.