Count and remove the unused blobs for Sitecore 10.2. Replaces the use of https://gist.github.com/michaellwest/51f4bcaf93400649b5482cf061d0e869

CleanUnusedBlobs.sql

/* Modified version of the cleanup script provided by Sitecore Support. This version runs with a counter to help run in small batches. */

create table #UnusedBlobIDs (
    ID UNIQUEIDENTIFIER PRIMARY KEY (ID)
);
 
WITH [ExistingBlobs] ([BlobId]) AS (
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [SharedFields]
    ON '{' + CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) + '}' = [SharedFields].[Value]
    UNION
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [SharedFields]
    ON CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) = [SharedFields].[Value]
    UNION
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [VersionedFields]
    ON '{' + CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) + '}' = [VersionedFields].[Value]
    UNION
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [VersionedFields]
    ON CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) = [VersionedFields].[Value]
    UNION
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [UnversionedFields]
    ON '{' + CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) + '}' = [UnversionedFields].[Value]
    UNION
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [UnversionedFields]
    ON CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) = [UnversionedFields].[Value]
    UNION
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [ArchivedFields]
    ON '{' + CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) + '}' = [ArchivedFields].[Value]
    UNION
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [ArchivedFields]
    ON CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) = [ArchivedFields].[Value]
)
     
INSERT INTO #UnusedBlobIDs (ID) SELECT DISTINCT [Blobs].[BlobId]
FROM [Blobs]
WHERE NOT EXISTS
(
    SELECT NULL
    FROM [ExistingBlobs]
    WHERE [ExistingBlobs].[BlobId] = [Blobs].[BlobId]
)

DECLARE @r INT;
DECLARE @batchsize INT;
DECLARE @counter INT;

SET @r = 1;
SET @batchsize=1000;
SET @counter = 0

WHILE (@r > 0 AND @counter < 10000)
    BEGIN
        BEGIN TRANSACTION;
        DELETE TOP (@batchsize) FROM [Blobs] where [Blobs].[BlobId] IN (SELECT ID from #UnusedBlobIDs);
        SET @r = @@ROWCOUNT;
        SET @counter = @counter + @r
        COMMIT TRANSACTION;
    END
 
DROP TABLE #UnusedBlobIDs;

CountBlobsTotal.sql

/* Count all the rows in the Blobs table. Considerably faster than SELECT COUNT(1) FROM [Blobs] */
SELECT
   Total_Rows= SUM(st.row_count)
FROM
   sys.dm_db_partition_stats st
WHERE
    object_name(object_id) = 'Blobs' AND (index_id < 2)

CountUnusedBlobs.sql

/* Returns the count of unused blobs both in total and a unique list. */
WITH [ExistingBlobs] ([BlobId]) AS (
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [SharedFields]
    ON '{' + CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) + '}' = [SharedFields].[Value]
    UNION
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [SharedFields]
    ON CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) = [SharedFields].[Value]
    UNION
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [VersionedFields]
    ON '{' + CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) + '}' = [VersionedFields].[Value]
    UNION
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [VersionedFields]
    ON CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) = [VersionedFields].[Value]
    UNION
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [UnversionedFields]
    ON '{' + CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) + '}' = [UnversionedFields].[Value]
    UNION
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [UnversionedFields]
    ON CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) = [UnversionedFields].[Value]
    UNION
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [ArchivedFields]
    ON '{' + CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) + '}' = [ArchivedFields].[Value]
    UNION
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [ArchivedFields]
    ON CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) = [ArchivedFields].[Value]
)

SELECT 
  COUNT([Blobs].[BlobId]) as [UnusedCount], 
  COUNT(DISTINCT [Blobs].[BlobId]) as [UnusedDistinctCount] 
  FROM [Blobs]
  LEFT JOIN [ExistingBlobs] ON [Blobs].[BlobId] = [ExistingBlobs].[BlobId]
WHERE [ExistingBlobs].[BlobId] IS NULL

SitecoreSupport-CleanupUnusedBlobs.sql

DECLARE @r INT;
DECLARE @batchsize INT;

SET @r = 1;
SET @batchsize=1000;
 
create table #UnusedBlobIDs (
    ID UNIQUEIDENTIFIER PRIMARY KEY (ID)
);
 
WITH [ExistingBlobs] ([BlobId]) AS (
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [SharedFields]
    ON '{' + CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) + '}' = [SharedFields].[Value]
    UNION
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [SharedFields]
    ON CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) = [SharedFields].[Value]
    UNION
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [VersionedFields]
    ON '{' + CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) + '}' = [VersionedFields].[Value]
    UNION
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [VersionedFields]
    ON CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) = [VersionedFields].[Value]
    UNION
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [UnversionedFields]
    ON '{' + CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) + '}' = [UnversionedFields].[Value]
    UNION
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [UnversionedFields]
    ON CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) = [UnversionedFields].[Value]
    UNION
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [ArchivedFields]
    ON '{' + CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) + '}' = [ArchivedFields].[Value]
    UNION
    SELECT [Blobs].[BlobId]
    FROM [Blobs]
    JOIN [ArchivedFields]
    ON CONVERT(NVARCHAR(MAX), [Blobs].[BlobId]) = [ArchivedFields].[Value]
)
     
INSERT INTO #UnusedBlobIDs (ID) SELECT DISTINCT [Blobs].[BlobId]
FROM [Blobs]
WHERE NOT EXISTS
(
    SELECT NULL
    FROM [ExistingBlobs]
    WHERE [ExistingBlobs].[BlobId] = [Blobs].[BlobId]
)

WHILE @r > 0
    BEGIN
        BEGIN TRANSACTION;
        DELETE TOP (@batchsize) FROM [Blobs] where [Blobs].[BlobId] IN (SELECT ID from #UnusedBlobIDs);
        SET @r = @@ROWCOUNT;
        COMMIT TRANSACTION;
    END
 
DROP TABLE #UnusedBlobIDs;