Reduce noise from get_installed_extensions during e.g shut down (#12479)

All Errors that can occur during get_installed_extensions() come from
tokio-postgres functions, e.g. if the database is being shut down
("FATAL: terminating connection due to administrator command"). I'm
seeing a lot of such errors in the logs with the regression tests, with
very verbose stack traces. The compute_ctl stack trace is pretty useless
for errors originating from the Postgres connection, the error message
has all the information, so stop printing the stack trace.

I changed the result type of the functions to return the originating
tokio_postgres Error rather than anyhow::Error, so that if we introduce
other error sources to the functions where the stack trace might be
useful, we'll be forced to revisit this, probably by introducing a new
Error type that separates postgres errors from other errors. But this
will do for now.

compute_tools/src/compute.rs

@@ -2487,7 +2487,7 @@ pub async fn installed_extensions(conf: tokio_postgres::Config) -> Result<()> {
                 serde_json::to_string(&extensions).expect("failed to serialize extensions list")
             );
         }
-        Err(err) => error!("could not get installed extensions: {err:?}"),
+        Err(err) => error!("could not get installed extensions: {err}"),
     }
     Ok(())
 }

compute_tools/src/installed_extensions.rs

@@ -2,6 +2,7 @@ use std::collections::HashMap;
 
 use anyhow::Result;
 use compute_api::responses::{InstalledExtension, InstalledExtensions};
+use tokio_postgres::error::Error as PostgresError;
 use tokio_postgres::{Client, Config, NoTls};
 
 use crate::metrics::INSTALLED_EXTENSIONS;
@@ -10,7 +11,7 @@ use crate::metrics::INSTALLED_EXTENSIONS;
 /// and to make database listing query here more explicit.
 ///
 /// Limit the number of databases to 500 to avoid excessive load.
-async fn list_dbs(client: &mut Client) -> Result<Vec<String>> {
+async fn list_dbs(client: &mut Client) -> Result<Vec<String>, PostgresError> {
     // `pg_database.datconnlimit = -2` means that the database is in the
     // invalid state
     let databases = client
@@ -37,7 +38,9 @@ async fn list_dbs(client: &mut Client) -> Result<Vec<String>> {
 /// Same extension can be installed in multiple databases with different versions,
 /// so we report a separate metric (number of databases where it is installed)
 /// for each extension version.
-pub async fn get_installed_extensions(mut conf: Config) -> Result<InstalledExtensions> {
+pub async fn get_installed_extensions(
+    mut conf: Config,
+) -> Result<InstalledExtensions, PostgresError> {
     conf.application_name("compute_ctl:get_installed_extensions");
     let databases: Vec<String> = {
         let (mut client, connection) = conf.connect(NoTls).await?;