test(nix): wire pg_isolation_regress into the check harness

nix/checks.nix

@@ -34,7 +34,7 @@
             }:
             let
               pg_prove = pkgs.perlPackages.TAPParserSourceHandlerpgTAP;
-              inherit (self'.packages) pg_regress;
+              inherit (self'.packages) pg_regress pg_isolation_regress;
               getkey-script = pkgs.stdenv.mkDerivation {
                 name = "pgsodium-getkey";
                 buildCommand = ''
@@ -273,6 +273,11 @@
                   testList;
 
               sortedTestList = builtins.sort (a: b: a < b) filteredTestList;
+
+              # Concurrency/isolation specs run via pg_isolation_regress (the stock
+              # PostgreSQL isolation tester). Specs live in tests/isolation/specs/,
+              # expected output in tests/isolation/expected/. Add new spec names here.
+              isolationSpecList = [ "sample_isolation" ];
             in
             pkgs.writeShellApplication rec {
               name = "postgres-${pgpkg.version}-check-harness";
@@ -287,6 +292,7 @@
                 pgpkg
                 pg_prove
                 pg_regress
+                pg_isolation_regress
                 procps
                 start-postgres-server-bin
                 which
@@ -556,6 +562,37 @@
                 fi
                 log info "pg_regress tests completed successfully"
 
+                # Isolation (concurrency) tests via pg_isolation_regress -- the stock
+                # PostgreSQL isolation tester shipped in the build. Reuses the same
+                # running server as pg_regress (--use-existing). These specs target
+                # core/heap + contrib concurrency behaviour. Skipped on:
+                #   - CLI variants: portable build runs only a test subset.
+                #   - orioledb ships its own isolation suite for its storage-engine 
+                #     concurrency semantics.
+                #shellcheck disable=SC2193
+                if ${lib.boolToString isCliVariant}; then
+                  log info "CLI variant detected - skipping isolation tests"
+                elif [[ "${pgpkg.version}" == *"_"* ]]; then
+                  log info "orioledb variant detected - skipping isolation tests (orioledb has its own isolation suite)"
+                else
+                  log info "Running pg_isolation_regress tests (${builtins.toString (builtins.length isolationSpecList)} specs)"
+                  mkdir -p "$out/isolation_output"
+                  if ! log_cmd pg_isolation_regress \
+                    --use-existing \
+                    --dbname=postgres \
+                    --inputdir=${./tests/isolation} \
+                    --outputdir="$out/isolation_output" \
+                    --host=localhost \
+                    --port=${pgPort} \
+                    --user=supabase_admin \
+                    ${builtins.concatStringsSep " " isolationSpecList} 2>&1; then
+                    log error "pg_isolation_regress tests failed"
+                    cat "$out/isolation_output/output_iso/regression.diffs" 2>/dev/null || cat "$out/isolation_output/regression.diffs" 2>/dev/null || true
+                    exit 1
+                  fi
+                  log info "pg_isolation_regress tests completed successfully"
+                fi
+
                 # Skip migrations tests for CLI variants (they may depend on extensions)
                 if ${lib.boolToString isCliVariant}; then
                   log info "CLI variant detected - skipping migrations tests"
@@ -890,6 +927,7 @@
             goss
             image-size-analyzer
             pg_regress
+            pg_isolation_regress
             pg-startup-profiler
             supabase-cli
             supascan

nix/ext/pg_isolation_regress.nix

@@ -0,0 +1,29 @@
+{
+  lib,
+  stdenv,
+  postgresql,
+}:
+
+stdenv.mkDerivation {
+  pname = "pg_isolation_regress";
+  version = postgresql.version;
+
+  phases = [ "installPhase" ];
+
+  # pg_isolation_regress and its helper isolationtester are built as part of the
+  # standard PostgreSQL source tree (src/test/isolation) and ship in the pgxs
+  # tree. pg_isolation_regress locates isolationtester relative to its own
+  # binary, so both must live in the same directory.
+  installPhase = ''
+    mkdir -p $out/bin
+    cp ${postgresql}/lib/pgxs/src/test/isolation/pg_isolation_regress $out/bin/
+    cp ${postgresql}/lib/pgxs/src/test/isolation/isolationtester $out/bin/
+  '';
+
+  meta = with lib; {
+    description = "Concurrent-isolation regression testing tool for PostgreSQL";
+    homepage = "https://www.postgresql.org/";
+    platforms = postgresql.meta.platforms;
+    license = licenses.postgresql;
+  };
+}

nix/packages/default.nix

@@ -18,6 +18,13 @@
           postgresqlPackage = self'.packages."postgresql_${version}";
         in
         pkgs.callPackage ../ext/pg_regress.nix { postgresql = postgresqlPackage; };
+      # Function to create the pg_isolation_regress package
+      makePgIsolationRegress =
+        version:
+        let
+          postgresqlPackage = self'.packages."postgresql_${version}";
+        in
+        pkgs.callPackage ../ext/pg_isolation_regress.nix { postgresql = postgresqlPackage; };
       pgsqlSuperuser = "supabase_admin";
       supascan-pkgs = pkgs.callPackage ./supascan.nix {
         inherit (pkgs) lib;
@@ -67,6 +74,7 @@
           pg-restore = pkgs.callPackage ./pg-restore.nix { psql_15 = self'.packages."psql_15/bin"; };
           pg_prove = pkgs.perlPackages.TAPParserSourceHandlerpgTAP;
           pg_regress = makePgRegress activeVersion;
+          pg_isolation_regress = makePgIsolationRegress activeVersion;
           run-testinfra = pkgs.callPackage ./run-testinfra.nix { };
           show-commands = pkgs.callPackage ./show-commands.nix { };
           start-client = pkgs.callPackage ./start-client.nix {

nix/tests/isolation/expected/sample_isolation.out

@@ -0,0 +1,20 @@
+Parsed test spec with 2 sessions
+
+starting permutation: s1_begin s1_update s2_begin s2_read s1_commit s2_read s2_commit
+step s1_begin: BEGIN;
+step s1_update: UPDATE iso_sample SET val = val + 1 WHERE id = 1;
+step s2_begin: BEGIN ISOLATION LEVEL READ COMMITTED;
+step s2_read: SELECT val FROM iso_sample WHERE id = 1;
+val
+---
+100
+(1 row)
+
+step s1_commit: COMMIT;
+step s2_read: SELECT val FROM iso_sample WHERE id = 1;
+val
+---
+101
+(1 row)
+
+step s2_commit: COMMIT;

nix/tests/isolation/specs/sample_isolation.spec

@@ -0,0 +1,31 @@
+# Sample isolation spec -- proves the pg_isolation_regress harness runs in CI.
+# This is not a regression test for any particular fix; it just exercises the
+# stock PostgreSQL isolation tester so real concurrency specs (e.g. MERGE
+# serialization, postgres_fdw EvalPlanQual) can be dropped in alongside it.
+#
+# Scenario: session s2 reads a row under READ COMMITTED before and after a
+# concurrent UPDATE+COMMIT by session s1 -- the second read observes the
+# committed change. No step blocks.
+
+setup
+{
+  CREATE TABLE iso_sample (id int PRIMARY KEY, val int);
+  INSERT INTO iso_sample VALUES (1, 100);
+}
+
+teardown
+{
+  DROP TABLE iso_sample;
+}
+
+session s1
+step s1_begin  { BEGIN; }
+step s1_update { UPDATE iso_sample SET val = val + 1 WHERE id = 1; }
+step s1_commit { COMMIT; }
+
+session s2
+step s2_begin  { BEGIN ISOLATION LEVEL READ COMMITTED; }
+step s2_read   { SELECT val FROM iso_sample WHERE id = 1; }
+step s2_commit { COMMIT; }
+
+permutation s1_begin s1_update s2_begin s2_read s1_commit s2_read s2_commit