Index seek instead of index scan for is not null in condition

Question

I have the query below...

SELECT Compra_ID
FROM [Fart_Compras_dss_tracking]
WHERE [local_create_peer_timestamp] IS NOT NULL

CREATE TABLE [DataSync].[Fart_Compras_dss_tracking]
(
    [COMPRA_ID] [int] NOT NULL,
    [Sucursal_ID] [int] NOT NULL,
    [update_scope_local_id] [int] NULL,
    [scope_update_peer_key] [int] NULL,
    [scope_update_peer_timestamp] [bigint] NULL,
    [local_update_peer_key] [int] NOT NULL,
    [local_update_peer_timestamp] [timestamp] NOT NULL,
    [create_scope_local_id] [int] NULL,
    [scope_create_peer_key] [int] NULL,
    [scope_create_peer_timestamp] [bigint] NULL,
    [local_create_peer_key] [int] NOT NULL,
    [local_create_peer_timestamp] [bigint] NOT NULL,
    [sync_row_is_tombstone] [int] NOT NULL,
    [last_change_datetime] [datetime] NULL,

    CONSTRAINT [PK_DataSync.Fart_Compras_dss_tracking] 
        PRIMARY KEY CLUSTERED ([COMPRA_ID] ASC, [Sucursal_ID] ASC)
                WITH (STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]
GO

CREATE NONCLUSTERED INDEX [Idx_Text_4] 
ON [DataSync].[Fart_Compras_dss_tracking] ([COMPRA_ID] ASC,
                                           [Sucursal_ID] ASC,
                                           [local_create_peer_timestamp] ASC,
                                           [local_update_peer_timestamp] ASC)
INCLUDE ([update_scope_local_id], [scope_update_peer_key],
         [scope_update_peer_timestamp], [local_update_peer_key],
         [create_scope_local_id], [scope_create_peer_key],
         [scope_create_peer_timestamp], [local_create_peer_key],
         [sync_row_is_tombstone], [last_change_datetime]) 
WHERE ([local_create_peer_timestamp] IS NOT NULL)
WITH (STATISTICS_NORECOMPUTE = OFF, DROP_EXISTING = OFF, ONLINE = OFF) ON [PRIMARY]
GO

Execution plan is available in the link below...

https://www.brentozar.com/pastetheplan/?id=SkZbOe8zi

When I take a look at the execution plan it shows INDEX SCAN, I tried creating different indexes/filtered indexes, but I am not able to see INDEX SEEK even forcing the usage of my indexes.

What index is required to improve performance for IS NOT NULL conditions like this?

Answer 1

The index you showed us isn't suitable for optimizing your filter condition. (It does seem to be quicker to scan than your PK clustered index, but a scan is still required.)

This index will help performance.

CREATE INDEX tstamp ON Fart_Compras_dss_tracking 
      (local_create_peer_timestamp);

It can be random-accessed by your WHERE filter. You'll still see an index range scan.