Re: Need an idea to operate massive delete operation on big size table.

You're absolutely right—PostgreSQL doesn't have a DISABLE clause for
indexes or constraints like some other databases (e.g., SQL Server).
However, there are still ways to work around this limitation and optimize
large delete operations in PostgreSQL. Here are some PostgreSQL-specific
strategies:

1. **Batch Deletion**: Delete in small chunks using `LIMIT` or `CTE`.
```sql
DELETE FROM your_table WHERE <condition> LIMIT 10000;
```

2. **Drop and Recreate Indexes**: Drop indexes before deletion, then
recreate them.
```sql
DROP INDEX idx_name;
DELETE FROM your_table WHERE <condition>;
CREATE INDEX idx_name ON your_table(column_name);
```

3. **Partitioning**: Use table partitioning to drop entire partitions
instead of deleting rows.
```sql
DROP TABLE your_table_partition_name;
```

4. **Archive and Truncate**: Copy rows to keep into a temp table, truncate
the original, then reinsert.
```sql
CREATE TABLE temp_table AS SELECT * FROM your_table WHERE
<condition_to_keep>;
TRUNCATE TABLE your_table;
INSERT INTO your_table SELECT * FROM temp_table;
DROP TABLE temp_table;
```

5. **Disable Triggers**: Temporarily disable triggers during deletion.
```sql
ALTER TABLE your_table DISABLE TRIGGER ALL;
DELETE FROM your_table WHERE <condition>;
ALTER TABLE your_table ENABLE TRIGGER ALL;
```

6. **Optimize Settings**: Increase `work_mem` and `maintenance_work_mem`
for the session.
```sql
SET work_mem = '1GB';
SET maintenance_work_mem = '2GB';
```

7. **Vacuum and Analyze**: Clean up after deletion.
```sql
VACUUM ANALYZE your_table;
```

8. **Soft Deletes**: Use an `is_deleted` flag to mark rows for later
cleanup.

By batching, partitioning, and optimizing settings, you can make large
deletes faster and less disruptive.

Le mer. 15 janv. 2025 à 16:22, Ron Johnson <ronljohnsonjr(at)gmail(dot)com> a
écrit :

> Sadly, Postgresql does not have (super-handy) "DISABLE" clauses.
>
> On Wed, Jan 15, 2025 at 10:12 AM youness bellasri <
> younessbellasri(at)gmail(dot)com> wrote:
>
>> 1. *Batch Deletion*
>>
>> Instead of deleting all records at once, break the operation into smaller
>> batches. This reduces locking, transaction log growth, and the risk of
>> timeouts.
>> 2. *Use Indexes*
>>
>> Ensure that the columns used in the WHERE clause of the delete queries
>> are indexed. This speeds up the identification of rows to delete.
>> 3. *Disable Indexes and Constraints Temporarily*
>>
>> If the table has many indexes or constraints, disabling them during the
>> delete operation can speed up the process. Re-enable them afterward.
>>
>> Le mer. 15 janv. 2025 à 16:08, Ron Johnson <ronljohnsonjr(at)gmail(dot)com> a
>> écrit :
>>
>>> On Wed, Jan 15, 2025 at 9:54 AM Gambhir Singh <gambhir(dot)singh05(at)gmail(dot)com>
>>> wrote:
>>>
>>>> Hi,
>>>>
>>>> I received a request from a client to delete duplicate records from a
>>>> table which is very large in size.
>>>>
>>>> Delete queries (~2 Billion) are provided via file, and we have to
>>>> execute that file in DB. Last time it lasted for two days. I feel there
>>>> must be another way to delete records in an efficient manner
>>>>
>>>
>>> Maybe the delete "queries" are poorly written. Maybe there's no
>>> supporting index.
>>>
>>>
> --
> Death to <Redacted>, and butter sauce.
> Don't boil me, I'm still alive.
> <Redacted> lobster!
>