[docs] Add instructions to recreate a partition index

docs/content/stable/api/ysql/the-sql-language/statements/ddl_create_index.md

@@ -372,6 +372,53 @@ DROP INDEX uniqueerror_i_idx;
 DROP INDEX
 ```
 
+### Recreate a partition index
+
+Suppose you have a partitioned table where the parent has a unique constraint.
+To recreate indexes, you should avoid directly creating an index on the partitioned table (parent table) because that cannot use `CONCURRENTLY`.
+Follow these steps to recreate a partition index online:
+
+```plpgsql
+-- Set up example
+CREATE TABLE parent (i int UNIQUE) PARTITION BY RANGE (i);
+CREATE TABLE child0 PARTITION OF parent FOR VALUES FROM (0) TO (100000);
+CREATE TABLE child1 PARTITION OF parent FOR VALUES FROM (100000) TO (200000);
+CREATE TABLE child2 PARTITION OF parent FOR VALUES FROM (200000) TO (300000);
+INSERT INTO parent VALUES (generate_series(0, 299999));
+
+-- 1. Build standalone unique index (slow, but non-blocking)
+CREATE UNIQUE INDEX CONCURRENTLY child0_i_unique ON child0 (i);
+-- 2. Add CHECK constraint matching partition bounds (fast: no scan)
+ALTER TABLE child0 ADD CONSTRAINT child0_partition_check
+  CHECK (i IS NOT NULL AND i >= 0 AND i < 100000) NOT VALID;
+-- 3. Validate the CHECK (slow, but non-blocking on parent)
+ALTER TABLE child0 VALIDATE CONSTRAINT child0_partition_check;
+-- 4. Lock the parent to prevent queries from missing the partition's data
+--    while it is detached.
+BEGIN;
+LOCK TABLE parent IN ACCESS EXCLUSIVE MODE;
+-- 5. Detach (fast)
+ALTER TABLE parent DETACH PARTITION child0;
+-- 6. Drop inherited constraint (fast: drops old backing index)
+ALTER TABLE child0 DROP CONSTRAINT child0_i_key;
+-- 7. Promote standalone index to a constraint (fast: no rebuild)
+ALTER TABLE child0 ADD CONSTRAINT child0_i_key UNIQUE USING INDEX child0_i_unique;
+-- 8. Reattach (fast: CHECK and UNIQUE already satisfy parent)
+ALTER TABLE parent ATTACH PARTITION child0 FOR VALUES FROM (0) TO (100000);
+COMMIT;
+-- 9. Drop temporary CHECK constraint
+ALTER TABLE child0 DROP CONSTRAINT child0_partition_check;
+```
+
+Repeat steps 1–9 for `child1`, `child2`, and any other partitions as needed.
+Step 4 to lock the parent is optional if there will be no reads or writes against the parent table while the partition is detached.
+
+{{< note title="Note" >}}
+
+Step 4 requires object locking support (available since 2025.2): set YB-TServer flags `enable_object_locking_for_table_locks=true` and `ysql_yb_ddl_transaction_block_enabled=true`.
+
+{{< /note >}}
+
 ### Common errors and solutions
 
 - `ERROR:  duplicate key value violates unique constraint "uniqueerror_i_idx"`