This adds a new log line that shows each schema cache query time individually, only on
`log-level=debug`. Like so:
```
$ PGRST_LOG_LEVEL=debug postgrest-with-pg-17 -f test/spec/fixtures/load.sql postgrest-run
....
10/Apr/2026:21:48:45 -0500: Schema cache queried in 192.2 milliseconds
10/Apr/2026:21:48:45 -0500: tables: 72.027 ms, keydeps: 20.118 ms, rels: 6.189 ms, funcs: 35.010 ms, comprels: 4.319 ms, dreps: 1.614 ms, mhandlers: 7.419 ms, tzones: 43.025 ms
```
This helps debug specific schema cache queries being slow like on
https://github.com/PostgREST/postgrest/issues/4613#issuecomment-4210191065 and
https://github.com/PostgREST/postgrest/issues/3046#issuecomment-3469059948.
It also closes https://github.com/PostgREST/postgrest/issues/3215,
which main motivation was to find out which query is slow.
Implementation details
---------------------
To time each query inside a transaction in pure SQL, we do:
```sql
-- start timer
select set_config('pgrst.tmp_x', clock_timestamp()::text, false);
-- run the query
select <query>
-- end timer
select set_config('pgrst.tmp_x', (clock_timestamp() - current_setting('pgrst.tmp_x', false)::timestamptz)::text, false);
-- .... repeated for every query
-- at the end we capture all the timings with
select extract('milliseconds' from current_setting('pgrst.tmp_x', false)::interval), extract(..;
```
Considerations
--------------
Only added this on `log-level=debug` because while the queries are fast
and the data is valuable, it triples the amount of queries we run during schema cache refresh,
which could be troublesome on slow networks. It's possible to reduce the
amount of queries by starting and stopping timers in one statement, but
this would still double the amount of queries and makes the code messy,
doesn't seem worth it.
Also it would pollute pg_stat_statements, it's only required to debug certain
extreme cases anyway.
This commit addresses the following TODO in observationMessage function:
"TODO pending refactor: The logic for printing the query cannot be done here. Join the observationMessages function into observationLogger to avoid this mempty."
Changing observationMessage to observationMessages (that returns [Text] instead of Text) made it possible to address issue documented as TODO and harmonize query logging with other observations.
There is unnecessary coupling between observation messages and emited log entries. This causes schema loading logic to emit redundant events: SchemaCacheSummaryObs and SchemaCacheLoadedObs.
Logically - we want to emit a single event containing both summary and timing information. How it is logged is a different matter and should be decoupled.
This commit
* changes observationMessage function returning Text to observationMessages returning [Text] so that it is possible to return multiple (or zero) messages to log based on an observation event
* Removes SchemaCacheSummaryObs constructor from Observation type and adds summary text to SchemaCacheLoadedObs
Observation module exports observationMessage and isDbListenerBug functions. The first one is used only in Logger module and the second one - only in Listener.
This change moves observationMessage function to Logger module and isDbListenerBug function to Listener module, making all three modules more cohesive and lessening dependencies.
It also gives the compiler more opportunities for intra-module inlining and optimization.
stateLogDebouncePoolTimeout is an MVar initialized on the first logging of PoolAcqTimeoutObs. The code in logWithDebounce has race condition that could lead to creation of multiple debouncers.
This change simplifies logic by getting rid of lazy initialization of debouncer.
PoolAcqTimeoutObs is always created with SQL.AcquisitionTimeoutUsageError so the parameter does not provide any useful information.
On the other hand, it complicates debouncing logic in Logger as logWithDebounce has to lazily create the debouncer (which is error prone and hence the logic has a race condition).
This change removes the parameter from PoolAcqTimeoutObs. It is a prerequisite to simplifying logWithDebounce.
Closes https://github.com/PostgREST/postgrest/issues/4226.
This requires moving query generation to the top App.hs module.
At this point is also simple to log the transaction variables + the
pre-request function call but this is not done here to reduce scope.
Changes:
1. Refactoring and some cleanup of JWT handling code:
* Instead of caching AuthResult cache decoded claims (which signature was verified). Validating claims and determining role is done after cache lookup
* Cleaned up API so that usage of it is simplified: lookupJwtCache cache key >>= parseClaims configJwtAud time
* Handling of JwtCacheState initialization and updates of configuration is encapsulated in Auth.JwtCache module
2. Generic high performance (hopefully) scalable, dynamically resizeable cache implementation based on stm, stm-hamt and sieve algorithm. It also integrates with PostgREST measurements infrastructure providing usage stats (ie. hit ratio, evictions count)
It used to be that this was only enabled with log-level=debug.
But the default log-level is misleading, for example:
```
$ PGRST_DB_SCHEMAS="apflora" postgrest-with-postgresql-16 -f test/io/big_schema.sql postgrest-run
...
13/Nov/2024:22:08:20 -0500: Config reloaded
13/Nov/2024:22:08:20 -0500: Schema cache queried in 36.3 milliseconds
13/Nov/2024:22:08:20 -0500: Schema cache loaded 326 Relations, 305 Relationships, 7 Functions, 0 Domain Representations, 4 Media Type Handlers, 1194 Timezones
```
The "Schema cache loaded" can take a while to appear, yet the 22:08:20
time is the same. If we reveal the load time this is clarified:
```
13/Nov/2024:22:08:37 -0500: Schema cache loaded in 16770.1 milliseconds
```
With this:
- Is no longer necessary to pass observer as an argument
to every function that needs observations.
- We can invoke the observer on every function that uses AppConfig.
However it'd be better to just call the observer in the upper modules
(like on App.hs).
