Re: Disable an index temporarily

On 20/04/14 03:02, Sergey Konoplev wrote:

Thanks for you reply.

>> an index can be INVALID (pg_index.indisvalid=false).
>>
>> I want to temporarily disable an index so that it won't be used to
>> access data but will still be updated.
>>
>> Can I simply set pg_index.indisvalid=false and later turn it true again?
>
> It works on a quick test, but I'm not sure how safe it is.
>
> If you need to test a query without the index use a transaction:
>
> Begin;
> Drop index ...;
> Explain ... select ...;
> Rollback;

I know about that.

The problem is I have a number of indexes in a large system that are
very similar. And I suspect some of them are superfluous.

Example:

btree (fmb_id, action_type)
btree (fmb_id)

Action_type in this case is one out of a handful of values (should
perhaps be an ENUM but is TEXT) and for most of the table the
combination of (fmb_id, action_type) is unique. The table itself has
~2E8 rows. So it takes a while to build these indexes from scratch.

Now, we have several performance counters in place. I want to disable
these indexes one by one and see what happens. I am probably not able to
find all of the queries that use them. But I believe that nothing much
happens if I drop one of them (preferably the former?).

Torsten