Fix double constraint creation for tables with EXCLUSION indexes

src/bin/pgcopydb/indexes.c

@@ -1267,6 +1267,30 @@ copydb_create_constraints(CopyDataSpec *specs, PGSQL *dst, SourceTable *table)
 			break;
 		}
 
+		/*
+		 * Idempotency guard: if this constraint already has a done_time in the
+		 * summary, a previous pass created it, so skip it rather than running
+		 * ALTER TABLE ADD CONSTRAINT again (which fails with "index ... is
+		 * already associated with a constraint"). Look up into a throwaway
+		 * spec so the command just prepared into indexSpecs is preserved.
+		 */
+		CopyIndexSpec doneCheck = { .sourceIndex = index };
+
+		if (!summary_lookup_constraint(sourceDB, &doneCheck))
+		{
+			/* errors have already been logged */
+			success = false;
+			break;
+		}
+
+		if (doneCheck.summary.doneTime > 0)
+		{
+			log_debug("Skipping constraint %s: already created (done at %lld)",
+					  index->constraintName,
+					  (long long) doneCheck.summary.doneTime);
+			continue;
+		}
+
 		if (!summary_add_constraint(sourceDB, &indexSpecs))
 		{
 			/* errors have already been logged */

src/bin/pgcopydb/summary.c

@@ -1424,7 +1424,7 @@ summary_add_constraint(DatabaseCatalog *catalog, CopyIndexSpec *indexSpecs)
 	}
 
 	char *sql =
-		"insert or replace into summary(pid, conoid, start_time_epoch, command)"
+		"insert or ignore into summary(pid, conoid, start_time_epoch, command)"
 		"values($1, $2, $3, $4)";
 
 	if (!semaphore_lock(&(catalog->sema)))
@@ -1780,46 +1780,32 @@ summary_table_count_indexes_left(DatabaseCatalog *catalog,
 
 	/*
 	 * When asked to create an index for a constraint and the index is neither
-	 * a UNIQUE nor a PRIMARY KEY index, then we can't use the ALTER TABLE ...
-	 * ADD CONSTRAINT ... USING INDEX ... command, because this only works with
-	 * UNIQUE and PRIMARY KEY indexes.
+	 * a UNIQUE nor a PRIMARY KEY index (such as an EXCLUSION constraint), then
+	 * we skip creating the index directly and instead create it as part of the
+	 * "plain" ALTER TABLE ... ADD CONSTRAINT ... command during the constraint
+	 * phase.
 	 *
-	 * This means that we have to skip creating the index first, and will only
-	 * then create it during the constraint phase, as part of the "plain" ALTER
-	 * TABLE ... ADD CONSTRAINT ... command.
-	 *
-	 * So when counting the indexes that are left to be created before we can
-	 * install the constraints, we should also skip counting these.
+	 * Even though we skip running CREATE INDEX for such indexes, each one is
+	 * still queued and processed by a worker, which calls
+	 * copydb_mark_index_as_done before checking whether all indexes are done.
+	 * We must therefore count these indexes here so that countIndexesLeft
+	 * reaches zero exactly once — when the last worker finishes its index —
+	 * rather than once per non-skipped index and again for each skipped index.
 	 */
 	char *sql =
 		"with idx(indexoid) as"
 		" ("
 		"  select i.oid as indexoid "
 		"    from s_table t join s_index i on i.tableoid = t.oid"
 		"   where tableoid = $1 "
-		" ), "
-		" skipidx(indexoid) as "
-		" ("
-		"  select i.oid as indexoid "
-		"    from s_table t "
-		"         join s_index i on i.tableoid = t.oid "
-		"         join s_constraint c on c.indexoid = i.oid "
-		"   where not i.isprimary and not i.isunique"
-		"     and tableoid = $2 "
-		" ),"
-		" indexlist(indexoid) as"
-		" ( "
-		"  select indexoid from idx "
-		"  except "
-		"  select indexoid from skipidx "
 		" ) "
-		" select count(l.indexoid) "
-		"   from indexlist l "
+		" select count(i.indexoid) "
+		"   from idx i "
 		"  where not exists "
 		"        ( "
 		"          select 1 "
 		"            from summary s "
-		"           where s.indexoid = l.indexoid "
+		"           where s.indexoid = i.indexoid "
 		"             and s.pid > 0 and s.done_time_epoch > 0"
 		"        ) ";
 
@@ -1843,7 +1829,6 @@ summary_table_count_indexes_left(DatabaseCatalog *catalog,
 
 	/* bind our parameters now */
 	BindParam params[] = {
-		{ BIND_PARAMETER_TYPE_INT64, "tableoid", table->oid, NULL },
 		{ BIND_PARAMETER_TYPE_INT64, "tableoid", table->oid, NULL }
 	};
 

tests/unit/expected/17-exclusion-with-pkey.out

@@ -0,0 +1,9 @@
+-[ RECORD 1 ]-----------------------------
+conname | excl_with_pkey_pkey
+contype | p
+condef  | PRIMARY KEY (id)
+-[ RECORD 2 ]-----------------------------
+conname | excl_with_pkey_excl
+contype | x
+condef  | EXCLUDE USING btree (val WITH =)
+

tests/unit/expected/6-exclusion-constraint-index-jobs.out

@@ -0,0 +1,24 @@
+CREATE DATABASE
+CREATE COLLATION
+-[ RECORD 1 ]-----------------------------
+conname | excl_with_pkey_pkey
+contype | p
+condef  | PRIMARY KEY (id)
+-[ RECORD 2 ]-----------------------------
+conname | excl_with_pkey_excl
+contype | x
+condef  | EXCLUDE USING btree (val WITH =)
+
+DROP DATABASE
+CREATE DATABASE
+CREATE COLLATION
+-[ RECORD 1 ]-----------------------------
+conname | excl_with_pkey_pkey
+contype | p
+condef  | PRIMARY KEY (id)
+-[ RECORD 2 ]-----------------------------
+conname | excl_with_pkey_excl
+contype | x
+condef  | EXCLUDE USING btree (val WITH =)
+
+DROP DATABASE

tests/unit/script/6-exclusion-constraint-index-jobs.sh

@@ -0,0 +1,58 @@
+#! /bin/bash
+
+set -x
+set -e
+
+# This script expects the following environment variables to be set:
+#
+#  - PGCOPYDB_SOURCE_PGURI
+#  - PGCOPYDB_TARGET_PGURI
+#
+# Regression test for the double constraint creation bug.
+#
+# Tables with both a PRIMARY KEY and an EXCLUSION constraint triggered
+# "ERROR: index is already associated with a constraint" with --index-jobs 1.
+# The bug was that EXCLUSION constraint indexes were excluded from the
+# "indexes remaining" count, causing copydb_create_constraints to be called
+# twice by the same worker when it processed the skipped EXCLUSION index.
+
+TARGET_BASE="${PGCOPYDB_TARGET_PGURI%/*}"
+
+for jobs in 1 4
+do
+    TMPDB="pgcopydb_excl_ij${jobs}"
+    TARGET_URI="${TARGET_BASE}/${TMPDB}"
+    TMPDIR="/tmp/pgcopydb-excl-ij${jobs}"
+
+    psql -q -d "${PGCOPYDB_TARGET_PGURI}" -c "CREATE DATABASE ${TMPDB}"
+
+    # The source schema contains a table using a custom collation.
+    # Pre-create it on the target so that --skip-collations works correctly.
+    psql -q -d "${TARGET_URI}" -c "
+        CREATE COLLATION IF NOT EXISTS mycol
+            (locale = 'fr-FR-x-icu', provider = 'icu');
+    "
+
+    pgcopydb clone \
+        --source "${PGCOPYDB_SOURCE_PGURI}" \
+        --target "${TARGET_URI}" \
+        --index-jobs "${jobs}" \
+        --table-jobs 2 \
+        --dir "${TMPDIR}" \
+        --not-consistent \
+        --skip-collations \
+        --fail-fast > /dev/null
+
+    # Verify both constraints survived the copy, using the same SQL as the
+    # SQL test suite. The SQL test covers a standard copy; this script
+    # additionally exercises --index-jobs 1 and --index-jobs 4 separately
+    # to catch the double-constraint-creation bug.
+    psql -d "${TARGET_URI}" \
+         --no-psqlrc \
+         --expanded \
+         --file ./sql/17-exclusion-with-pkey.sql
+
+    psql -q -d "${PGCOPYDB_TARGET_PGURI}" -c "DROP DATABASE ${TMPDB}"
+
+    rm -rf "${TMPDIR}"
+done

tests/unit/setup/17-exclusion-with-pkey.sql

@@ -0,0 +1,11 @@
+DROP TABLE IF EXISTS excl_with_pkey;
+
+CREATE TABLE excl_with_pkey (
+    id  integer NOT NULL,
+    val integer NOT NULL
+);
+
+ALTER TABLE excl_with_pkey ADD CONSTRAINT excl_with_pkey_pkey PRIMARY KEY (id);
+ALTER TABLE excl_with_pkey ADD CONSTRAINT excl_with_pkey_excl EXCLUDE USING btree (val WITH =);
+
+INSERT INTO excl_with_pkey VALUES (1, 10), (2, 20), (3, 30);

tests/unit/setup/setup.sql

@@ -13,3 +13,4 @@
 \ir 14-uuid.sql
 \ir 15-attgenerated.sql
 \ir 16-sequences.sql
+\ir 17-exclusion-with-pkey.sql

tests/unit/sql/17-exclusion-with-pkey.sql

@@ -0,0 +1,7 @@
+  select c.conname, c.contype, pg_get_constraintdef(c.oid) as condef
+    from pg_constraint c
+         join pg_class r on r.oid = c.conrelid
+         join pg_namespace n on n.oid = r.relnamespace
+   where n.nspname = 'public' and r.relname = 'excl_with_pkey'
+     and c.contype != 'n'  -- PostgreSQL 18 adds NOT NULL constraints to pg_constraint
+order by c.contype, c.conname;