diff --git a/kong/clustering/services/sync/hooks.lua b/kong/clustering/services/sync/hooks.lua
index 7a3a1402558d..336bd3226aa1 100644
--- a/kong/clustering/services/sync/hooks.lua
+++ b/kong/clustering/services/sync/hooks.lua
@@ -76,10 +76,16 @@ end
 
 
 function _M:entity_delta_writer(row, name, options, ws_id, is_delete)
+  -- composite key, like { id = ... }
+  local schema = kong.db[name].schema
+  local pk = schema:extract_pk_values(row)
+
+  assert(schema:validate_primary_key(pk))
+
   local deltas = {
     {
       type = name,
-      id = row.id,
+      pk = pk,
       ws_id = ws_id,
       row = is_delete and ngx_null or row,
     },
diff --git a/kong/clustering/services/sync/rpc.lua b/kong/clustering/services/sync/rpc.lua
index 978a355fb1a2..625b394d3505 100644
--- a/kong/clustering/services/sync/rpc.lua
+++ b/kong/clustering/services/sync/rpc.lua
@@ -274,7 +274,7 @@ local function do_sync()
 
     else
       -- delete the entity
-      local old_entity, err = kong.db[delta_type]:select({ id = delta.id, }) -- TODO: composite key
+      local old_entity, err = kong.db[delta_type]:select(delta.pk) -- composite key
       if err then
         return nil, err
       end
diff --git a/kong/clustering/services/sync/strategies/postgres.lua b/kong/clustering/services/sync/strategies/postgres.lua
index 589b9f025047..616a4e38cc78 100644
--- a/kong/clustering/services/sync/strategies/postgres.lua
+++ b/kong/clustering/services/sync/strategies/postgres.lua
@@ -67,21 +67,21 @@ local NEW_VERSION_QUERY = [[
     new_version integer;
   BEGIN
     INSERT INTO clustering_sync_version DEFAULT VALUES RETURNING version INTO new_version;
-    INSERT INTO clustering_sync_delta (version, type, id, ws_id, row) VALUES %s;
+    INSERT INTO clustering_sync_delta (version, type, pk, ws_id, row) VALUES %s;
   END $$;
 ]]
 
 
 -- deltas: {
---   { type = "service", "id" = "d78eb00f-8702-4d6a-bfd9-e005f904ae3e", "ws_id" = "73478cf6-964f-412d-b1c4-8ac88d9e85e9", row = "JSON", }
---   { type = "route", "id" = "0a5bac5c-b795-4981-95d2-919ba3390b7e", "ws_id" = "73478cf6-964f-412d-b1c4-8ac88d9e85e9", row = "JSON", }
+--   { type = "service", "pk" = { id = "d78eb00f..." }, "ws_id" = "73478cf6...", row = "JSON", }
+--   { type = "route", "pk" = { id = "0a5bac5c..." }, "ws_id" = "73478cf6...", row = "JSON", }
 -- }
 function _M:insert_delta(deltas)
   local buf = buffer.new()
   for _, d in ipairs(deltas) do
     buf:putf("(new_version, %s, %s, %s, %s)",
              self.connector:escape_literal(d.type),
-             self.connector:escape_literal(d.id),
+             self.connector:escape_literal(cjson_encode(d.pk)),
              self.connector:escape_literal(d.ws_id or kong.default_workspace),
              self.connector:escape_literal(cjson_encode(d.row)))
   end
diff --git a/kong/db/migrations/core/024_370_to_380.lua b/kong/db/migrations/core/024_370_to_380.lua
index 9d78807962cf..afb94a09f7a3 100644
--- a/kong/db/migrations/core/024_370_to_380.lua
+++ b/kong/db/migrations/core/024_370_to_380.lua
@@ -9,7 +9,7 @@ return {
       CREATE TABLE IF NOT EXISTS clustering_sync_delta (
         "version" INT NOT NULL,
         "type" TEXT NOT NULL,
-        "id" UUID NOT NULL,
+        "pk" JSON NOT NULL,
         "ws_id" UUID NOT NULL,
         "row" JSON,
         FOREIGN KEY (version) REFERENCES clustering_sync_version(version) ON DELETE CASCADE
diff --git a/spec/05-migration/db/migrations/core/024_370_to_380_spec.lua b/spec/05-migration/db/migrations/core/024_370_to_380_spec.lua
index 0563c4c83f80..f4a6145d16be 100644
--- a/spec/05-migration/db/migrations/core/024_370_to_380_spec.lua
+++ b/spec/05-migration/db/migrations/core/024_370_to_380_spec.lua
@@ -10,7 +10,7 @@ describe("database migration", function()
     assert.database_has_relation("clustering_sync_delta")
     assert.table_has_column("clustering_sync_delta", "version", "integer")
     assert.table_has_column("clustering_sync_delta", "type", "text")
-    assert.table_has_column("clustering_sync_delta", "id", "uuid")
+    assert.table_has_column("clustering_sync_delta", "pk", "json")
     assert.table_has_column("clustering_sync_delta", "ws_id", "uuid")
     assert.table_has_column("clustering_sync_delta", "row", "json")
   end)