From 0ca3311b261086ae86afb3b5877842a13728c808 Mon Sep 17 00:00:00 2001
From: Chris Munns <munns@planetscale.com>
Date: Fri, 24 Jul 2026 14:27:47 -0400
Subject: [PATCH] Re-drive index/constraint creation for split tables on
 --resume

For a table split into multiple parallel COPY parts, index and
constraint creation is gated on a per-run "who finished the last part"
election stored in the s_table_parts_done / s_table_indexes_done SQLite
tables (tableoid, pid). The gate only fires for the worker whose
getpid() matches the stored pid.

On --resume the stored pid belongs to a dead prior-run process, so no
live worker matches and the index/constraint enqueue is never
re-driven. A table whose parts all finished but whose PK constraint was
not yet built in the prior run stays with a bare leaf index, and
pg_restore post-data then fails to attach it (relation "..._pkey"
already exists / cannot attach index / no unique constraint matching
given keys).

Clear both election tables once at the start of a --resume clone,
single-threaded and before any table-data worker is forked, so a fresh
election runs among live workers. These tables only hold per-run
election tokens; progress comes from the summary table (done_time_epoch),
so clearing them loses no progress, and re-enqueue is idempotent.
---
 src/bin/pgcopydb/cli_clone_follow.c | 15 +++++++++++
 src/bin/pgcopydb/copydb.h           |  1 +
 src/bin/pgcopydb/copydb_schema.c    | 39 +++++++++++++++++++++++++++++
 3 files changed, 55 insertions(+)

diff --git a/src/bin/pgcopydb/cli_clone_follow.c b/src/bin/pgcopydb/cli_clone_follow.c
index b0ded2b2..ced0f1e1 100644
--- a/src/bin/pgcopydb/cli_clone_follow.c
+++ b/src/bin/pgcopydb/cli_clone_follow.c
@@ -773,6 +773,21 @@ cloneDB(CopyDataSpec *copySpecs)
 		return false;
 	}
 
+	/*
+	 * On --resume the per-run part/index election tables still hold the pids of
+	 * dead prior-run workers. Clear them now, single-threaded and before any
+	 * table-data worker is forked, so a fresh election among live workers
+	 * re-drives index/constraint creation for split (multi-part) tables.
+	 */
+	if (copySpecs->resume)
+	{
+		if (!copydb_resume_reset_part_election(copySpecs))
+		{
+			/* errors have already been logged */
+			return false;
+		}
+	}
+
 	/* now register in the catalogs the already known startTime */
 	if (!summary_start_timing(sourceDB, TIMING_SECTION_TOTAL))
 	{
diff --git a/src/bin/pgcopydb/copydb.h b/src/bin/pgcopydb/copydb.h
index b41454cb..cfd73b81 100644
--- a/src/bin/pgcopydb/copydb.h
+++ b/src/bin/pgcopydb/copydb.h
@@ -413,6 +413,7 @@ bool copydb_prepare_sequence_specs(CopyDataSpec *specs, PGSQL *pgsql, bool reset
 
 /* copydb_schema.c */
 bool copydb_fetch_schema_and_prepare_specs(CopyDataSpec *specs);
+bool copydb_resume_reset_part_election(CopyDataSpec *specs);
 bool copydb_objectid_is_filtered_out(CopyDataSpec *specs,
 									 uint32_t catalogOid,
 									 uint32_t oid,
diff --git a/src/bin/pgcopydb/copydb_schema.c b/src/bin/pgcopydb/copydb_schema.c
index 2aada56b..b9d4ee3f 100644
--- a/src/bin/pgcopydb/copydb_schema.c
+++ b/src/bin/pgcopydb/copydb_schema.c
@@ -179,6 +179,45 @@ copydb_fetch_schema_and_prepare_specs(CopyDataSpec *specs)
 }
 
 
+/*
+ * copydb_resume_reset_part_election clears the per-run "who finished last"
+ * election tables (s_table_parts_done, s_table_indexes_done) so that a
+ * --resume run holds a fresh election among live workers.
+ *
+ * These tables only ever store per-run election tokens (a tableoid and the
+ * getpid() of the worker that observed the last part/index as done); progress
+ * itself lives in the summary table (done_time_epoch). On resume the stored
+ * pids belong to dead prior-run processes, so no live worker matches and the
+ * index/constraint enqueue for a split (multi-part) table is never re-driven.
+ * Clearing the tokens loses no progress and re-enqueue is idempotent
+ * (IF NOT EXISTS / doneTime / foundConstraintOnTarget checks).
+ *
+ * Must run single-threaded before any COPY/table-data worker is forked, or the
+ * workers would race and wipe freshly-elected tokens.
+ */
+bool
+copydb_resume_reset_part_election(CopyDataSpec *specs)
+{
+	DatabaseCatalog *sourceDB = &(specs->catalogs.source);
+
+	log_notice("Resetting stale part/index election state for --resume");
+
+	if (!catalog_execute(sourceDB, "delete from s_table_parts_done"))
+	{
+		/* errors have already been logged */
+		return false;
+	}
+
+	if (!catalog_execute(sourceDB, "delete from s_table_indexes_done"))
+	{
+		/* errors have already been logged */
+		return false;
+	}
+
+	return true;
+}
+
+
 /*
  * copydb_fetch_source_catalog_setup initializes our local catalog cache and
  * checks the setup and cache state.