catalog: Add mz_overridden_system_parameters relation

Add `mz_internal.mz_overridden_system_parameters`, a materialized view
exposing environment-wide system parameter overrides set via `ALTER
SYSTEM`. It mirrors the existing `mz_cluster_system_parameters` and
`mz_replica_system_parameters` views, projecting the durable
`system_configurations` collection out of `mz_catalog_raw` where the
record kind is `ServerConfiguration`.

This lets any user observe the effective environment-wide overrides
without `SHOW ALL`, which only surfaces a limited set unless the session
is the highly privileged `mz_system` user.

Like the scoped views, it lists only parameters with an explicit
override. Parameters left at their default are absent.

Tests: extends the catalog testdrive listing and the autogenerated
mz_internal, oid, information_schema_tables, and catalog_server_explain
sqllogictest snapshots. Makes catalog_server_explain hermetic with a
`reset-server` directive so role OIDs from preceding files no longer leak
into its constant-folded plans.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: antiguru

doc/user/content/reference/system-catalog/mz_internal.md

@@ -820,6 +820,19 @@ The `mz_sessions` table contains a row for each active session in the system.
 | `connected_at`   | [`timestamp with time zone`]   | The time at which the session connected to the system.                                                                    |
 
 
+## `mz_overridden_system_parameters`
+
+The `mz_overridden_system_parameters` view contains a row for each system parameter whose
+environment-wide value differs from its default, as set by `ALTER SYSTEM`.
+Parameters left at their default are not listed.
+
+<!-- RELATION_SPEC mz_internal.mz_overridden_system_parameters -->
+| Field        | Type     | Meaning                                            |
+| ------------ | -------- | --------                                           |
+| `name`       | [`text`] | The name of the system parameter.                  |
+| `value`      | [`text`] | The environment-wide value of the system parameter. |
+
+
 ## `mz_cluster_system_parameters`
 
 The `mz_cluster_system_parameters` view contains a row for each cluster-coherent

src/catalog/src/builtin.rs

@@ -1186,6 +1186,7 @@ pub static BUILTINS_STATIC: LazyLock<Vec<Builtin<NameReference>>> = LazyLock::ne
         Builtin::Table(&MZ_AWS_CONNECTIONS),
         Builtin::Table(&MZ_SUBSCRIPTIONS),
         Builtin::Table(&MZ_SESSIONS),
+        Builtin::MaterializedView(&MZ_OVERRIDDEN_SYSTEM_PARAMETERS),
         Builtin::MaterializedView(&MZ_CLUSTER_SYSTEM_PARAMETERS),
         Builtin::MaterializedView(&MZ_REPLICA_SYSTEM_PARAMETERS),
         Builtin::MaterializedView(&MZ_DEFAULT_PRIVILEGES),

src/catalog/src/builtin/mz_internal.rs

@@ -2866,6 +2866,49 @@ pub static MZ_SESSIONS: LazyLock<BuiltinTable> = LazyLock::new(|| BuiltinTable {
     }),
 });
 
+pub static MZ_OVERRIDDEN_SYSTEM_PARAMETERS: LazyLock<BuiltinMaterializedView> =
+    LazyLock::new(|| BuiltinMaterializedView {
+        name: "mz_overridden_system_parameters",
+        schema: MZ_INTERNAL_SCHEMA,
+        oid: oid::MV_MZ_OVERRIDDEN_SYSTEM_PARAMETERS_OID,
+        desc: RelationDesc::builder()
+            .with_column("name", SqlScalarType::String.nullable(false))
+            .with_column("value", SqlScalarType::String.nullable(false))
+            .finish(),
+        column_comments: BTreeMap::from_iter([
+            ("name", "The name of the system parameter."),
+            (
+                "value",
+                "The environment-wide value of the system parameter.",
+            ),
+        ]),
+        // Projects the durable `system_configurations` collection (the
+        // `ALTER SYSTEM` set) out of `mz_catalog_raw` (the durable catalog as
+        // JSON): the key is `{name}` and the value is `{value}`. This surfaces
+        // only parameters with an explicit environment-wide override, mirroring
+        // the cluster- and replica-scoped views. Parameters left at their
+        // default are absent.
+        sql: "
+IN CLUSTER mz_catalog_server
+WITH (
+    ASSERT NOT NULL name,
+    ASSERT NOT NULL value
+) AS
+SELECT
+    data->'key'->>'name' AS name,
+    data->'value'->>'value' AS value
+FROM mz_internal.mz_catalog_raw
+WHERE data->>'kind' = 'ServerConfiguration'",
+        is_retained_metrics_object: false,
+        access: vec![PUBLIC_SELECT],
+        ontology: Some(Ontology {
+            entity_name: "system_parameter",
+            description: "Environment-wide system parameter overrides",
+            links: &const { [] },
+            column_semantic_types: &[],
+        }),
+    });
+
 pub static MZ_CLUSTER_SYSTEM_PARAMETERS: LazyLock<BuiltinMaterializedView> =
     LazyLock::new(|| BuiltinMaterializedView {
         name: "mz_cluster_system_parameters",

src/pgrepr-consts/src/oid.rs

@@ -805,3 +805,4 @@ pub const MV_MZ_CLUSTER_SYSTEM_PARAMETERS_OID: u32 = 17091;
 pub const MV_MZ_REPLICA_SYSTEM_PARAMETERS_OID: u32 = 17092;
 pub const FUNC_MZ_GEN_SERIES_UNOPT_OID: u32 = 17093;
 pub const FUNC_MZ_GEN_SERIES_UNOPT_STEP_OID: u32 = 17094;
+pub const MV_MZ_OVERRIDDEN_SYSTEM_PARAMETERS_OID: u32 = 17095;

test/sqllogictest/autogenerated/mz_internal.slt

@@ -452,6 +452,12 @@ role_id  text  The␠role␠ID␠of␠the␠role␠that␠the␠session␠is␠l
 client_ip  text  The␠IP␠address␠of␠the␠client␠that␠initiated␠the␠session.
 connected_at  timestamp␠with␠time␠zone  The␠time␠at␠which␠the␠session␠connected␠to␠the␠system.
 
+query TTT
+SELECT name, type, comment FROM objects WHERE schema = 'mz_internal' AND object = 'mz_overridden_system_parameters' ORDER BY position
+----
+name  text  The␠name␠of␠the␠system␠parameter.
+value  text  The␠environment-wide␠value␠of␠the␠system␠parameter.
+
 query TTT
 SELECT name, type, comment FROM objects WHERE schema = 'mz_internal' AND object = 'mz_cluster_system_parameters' ORDER BY position
 ----
@@ -812,6 +818,7 @@ mz_ontology_link_types
 mz_ontology_properties
 mz_ontology_semantic_types
 mz_optimizer_notices
+mz_overridden_system_parameters
 mz_pending_cluster_replicas
 mz_postgres_source_tables
 mz_postgres_sources

test/sqllogictest/catalog_server_explain.slt

@@ -51,6 +51,12 @@
 
 mode cockroach
 
+# Start from a pristine server so no user objects (e.g. roles created by a
+# preceding file in the same run) leak into the constant-folded plans. Several
+# `information_schema` views embed the current set of role OIDs as a literal,
+# which would otherwise make this snapshot depend on run order.
+reset-server
+
 # `mz_internal.mz_wallclock_global_lag` is a monotonic top-1 over a temporal
 # filter; planning it folds `mz_now()` into a literal millisecond timestamp that
 # changes on every run. Mask that one literal so the snapshot stays stable. The
@@ -4394,7 +4400,7 @@ mz_catalog.mz_materialized_views:
           Project: #4, #0, #5, #1, #6, #2, #9, #8, #3, #7
           Map: {=r/s1, s1=r/s1}, "s1"
       →Arrange (#1{schema_name}, #2{name})
-        →Constant (22 rows)
+        →Constant (23 rows)
       →Arrange (empty key) (#0{schema_name}) (#0{schema_name}, #1{name})
         →Fused with Child Map/Filter/Project
           Project: #4, #3, #5
@@ -4803,6 +4809,21 @@ Target cluster: mz_catalog_server
 
 EOF
 
+query T multiline
+EXPLAIN MATERIALIZED VIEW "mz_internal"."mz_overridden_system_parameters";
+----
+mz_internal.mz_overridden_system_parameters:
+  →Read mz_internal.mz_catalog_raw
+
+Source mz_internal.mz_catalog_raw
+  project=(#1, #2)
+  filter=(("ServerConfiguration" = (#0{data} ->> "kind")))
+  map=(((#0{data} -> "key") ->> "name"), ((#0{data} -> "value") ->> "value"))
+
+Target cluster: mz_catalog_server
+
+EOF
+
 query T multiline
 EXPLAIN SELECT * FROM "information_schema"."applicable_roles";
 ----
@@ -7019,7 +7040,7 @@ query T multiline
 EXPLAIN SELECT * FROM "mz_internal"."mz_builtin_materialized_views";
 ----
 Explained Query (fast path):
-  →Constant (22 rows)
+  →Constant (23 rows)
 
 Target cluster: mz_catalog_server
 
@@ -8883,7 +8904,7 @@ query T multiline
 EXPLAIN SELECT * FROM "mz_internal"."mz_ontology_entity_types";
 ----
 Explained Query (fast path):
-  →Constant (131 rows)
+  →Constant (132 rows)
 
 Target cluster: mz_catalog_server
 
@@ -8907,7 +8928,7 @@ Explained Query:
     cte l0 =
       →Differential Join %1:mz_schemas[#0{id}] » %2:mz_objects[#2{schema_id}] » %0[#0{schema_name}, #1{table_name}] » %3:mz_columns[#0{id}]
         →Arrange (#0{schema_name}, #1{table_name})
-          →Constant (131 rows)
+          →Constant (132 rows)
         →Arrange (#0{id})
           →Fused with Child Map/Filter/Project
             Project: #1, #3

test/sqllogictest/information_schema_tables.slt

@@ -517,6 +517,10 @@ mz_optimizer_notices
 BASE TABLE
 materialize
 mz_internal
+mz_overridden_system_parameters
+MATERIALIZED VIEW
+materialize
+mz_internal
 mz_pending_cluster_replicas
 MATERIALIZED VIEW
 materialize