sp_BlitzIndex: Added warning for persisted sample rates.

Author: ReeceGoding

Documentation/sp_BlitzIndex_Checks_by_Priority.md

@@ -6,8 +6,8 @@ Before adding a new check, make sure to add a Github issue for it first, and hav
 
 If you want to change anything about a check - the priority, finding, URL, or ID - open a Github issue first. The relevant scripts have to be updated too.
 
-CURRENT HIGH CHECKID: 124
-If you want to add a new check, start at 125.
+CURRENT HIGH CHECKID: 125
+If you want to add a new check, start at 126.
 
 | Priority | FindingsGroup           | Finding                                                         | URL                                                              | CheckID |
 | -------- | ----------------------- | --------------------------------------------------------------- | ---------------------------------------------------------------- | ------- |
@@ -25,6 +25,7 @@ If you want to add a new check, start at 125.
 | 80       | Abnormal Design Pattern | Filter Columns Not In Index Definition                          | https://www.brentozar.com/go/IndexFeatures                       | 34      |
 | 80       | Abnormal Design Pattern | History Table With NonClustered Index                           | https://sqlserverfast.com/blog/hugo/2023/09/an-update-on-merge/  | 124     |
 | 90       | Statistics Warnings     | Low Sampling Rates                                              | https://www.brentozar.com/go/stats                               | 91      |
+| 90       | Statistics Warnings     | Persisted Sampling Rates                                        | https://www.youtube.com/watch?v=V5illj_KOJg&t=758s               | 125     |
 | 90       | Statistics Warnings     | Statistics Not Updated Recently                                 | https://www.brentozar.com/go/stats                               | 90      |
 | 90       | Statistics Warnings     | Statistics with NO RECOMPUTE                                    | https://www.brentozar.com/go/stats                               | 92      |
 | 100      | Over-Indexing           | NC index with High Writes:Reads                                 | https://www.brentozar.com/go/IndexHoarder                        | 48      |

sp_BlitzIndex.sql

@@ -738,7 +738,8 @@ IF OBJECT_ID('tempdb..#dm_db_index_operational_stats') IS NOT NULL
 		  table_modify_date DATETIME NULL,
 		  no_recompute BIT NULL,
 		  has_filter BIT NULL,
-		  filter_definition NVARCHAR(MAX) NULL
+		  filter_definition NVARCHAR(MAX) NULL,
+		  has_persisted_sample BIT NULL
 		); 
 
 		CREATE TABLE #ComputedColumns
@@ -2279,7 +2280,7 @@ OPTION (RECOMPILE);';
 			INSERT #Statistics ( database_id, database_name, table_name, schema_name, index_name, column_names, statistics_name, last_statistics_update, 
 								days_since_last_stats_update, rows, rows_sampled, percent_sampled, histogram_steps, modification_counter, 
 								percent_modifications, modifications_before_auto_update, index_type_desc, table_create_date, table_modify_date,
-								no_recompute, has_filter, filter_definition)
+								no_recompute, has_filter, filter_definition, has_persisted_sample)
 				SELECT DB_ID(N' + QUOTENAME(@DatabaseName,'''') + N') AS [database_id], 
 				    @i_DatabaseName AS database_name,
 					obj.name AS table_name,
@@ -2306,7 +2307,12 @@ OPTION (RECOMPILE);';
 			        CONVERT(DATETIME, obj.modify_date) AS table_modify_date,
 					s.no_recompute,
 					s.has_filter,
-					s.filter_definition
+					s.filter_definition,
+					'
+					+ CASE WHEN (PARSENAME(@SQLServerProductVersion, 4) >= 15)
+					THEN N's.has_persisted_sample'
+					ELSE N'NULL AS has_persisted_sample' END
+			+ N'
 			FROM    ' + QUOTENAME(@DatabaseName) + N'.sys.stats AS s
 			JOIN    ' + QUOTENAME(@DatabaseName) + N'.sys.objects obj
 			ON      s.object_id = obj.object_id
@@ -2354,7 +2360,7 @@ OPTION (RECOMPILE);';
 			INSERT #Statistics(database_id, database_name, table_name, schema_name, index_name, column_names, statistics_name, 
 								last_statistics_update, days_since_last_stats_update, rows, modification_counter, 
 								percent_modifications, modifications_before_auto_update, index_type_desc, table_create_date, table_modify_date,
-								no_recompute, has_filter, filter_definition)
+								no_recompute, has_filter, filter_definition, has_persisted_sample)
 							SELECT DB_ID(N' + QUOTENAME(@DatabaseName,'''') + N') AS [database_id], 
 							    @i_DatabaseName AS database_name,
 								obj.name AS table_name,
@@ -2379,9 +2385,11 @@ OPTION (RECOMPILE);';
 								'
 								+ CASE WHEN @SQLServerProductVersion NOT LIKE '9%' 
 								THEN N's.has_filter,
-									   s.filter_definition' 
+									   s.filter_definition,' 
 								ELSE N'NULL AS has_filter,
-								       NULL AS filter_definition' END 
+								       NULL AS filter_definition,' END
+								/* If we are on this branch, then we cannot have the has_persisted_sample column (it is a 2019+ column). */
+								+ N'NULL AS has_persisted_sample'
 						+ N'								
 						FROM    ' + QUOTENAME(@DatabaseName) + N'.sys.stats AS s
 						INNER HASH JOIN    ' + QUOTENAME(@DatabaseName) + N'.sys.sysindexes si
@@ -4454,7 +4462,7 @@ BEGIN
 			END;
 
         ----------------------------------------
-        --Statistics Info: Check_id 90-99
+        --Statistics Info: Check_id 90-99, as well as 125
         ----------------------------------------
 
         RAISERROR(N'check_id 90: Outdated statistics', 0,1) WITH NOWAIT;
@@ -4503,6 +4511,24 @@ BEGIN
 		  OR (s.rows > 1000000 AND s.percent_sampled < 1)
 		OPTION    ( RECOMPILE );
 
+        RAISERROR(N'check_id 125: Statistics with a persisted sample rate', 0,1) WITH NOWAIT;
+                INSERT    #BlitzIndexResults ( check_id, Priority, findings_group, finding, [database_name], URL, details, index_definition,
+                                               secret_columns, index_usage_summary, index_size_summary )
+		SELECT  125 AS check_id,
+				90 AS Priority,
+				'Statistics Warnings' AS findings_group,
+				'Persisted Sampling Rates',
+				s.database_name,
+				'https://www.youtube.com/watch?v=V5illj_KOJg&t=758s' AS URL,
+				'The statistics sample rate/amount has been persisted here. ' + CONVERT(NVARCHAR(100), s.percent_sampled) + '% of the rows were sampled during the last statistics update. This may indicate that somebody is doing statistics rocket surgery. Perhaps you would be better off updating statistics more frequently?' AS details,
+				QUOTENAME(database_name) + '.' + QUOTENAME(s.schema_name) + '.' + QUOTENAME(s.table_name) + '.' + QUOTENAME(s.index_name) + '.' + QUOTENAME(s.statistics_name) + '.' + QUOTENAME(s.column_names) AS index_definition,
+				'N/A' AS secret_columns,
+				'N/A' AS index_usage_summary,
+				'N/A' AS index_size_summary
+		FROM #Statistics AS s
+		WHERE s.has_persisted_sample = 1
+		OPTION    ( RECOMPILE );
+
         RAISERROR(N'check_id 92: Statistics with NO RECOMPUTE', 0,1) WITH NOWAIT;
                 INSERT    #BlitzIndexResults ( check_id, Priority, findings_group, finding, [database_name], URL, details, index_definition,
                                                secret_columns, index_usage_summary, index_size_summary )
@@ -4521,7 +4547,6 @@ BEGIN
 		WHERE s.no_recompute = 1
 		OPTION    ( RECOMPILE );
 
-
 	     RAISERROR(N'check_id 94: Check Constraints That Reference Functions', 0,1) WITH NOWAIT;
                 INSERT    #BlitzIndexResults ( check_id, Priority, findings_group, finding, [database_name], URL, details, index_definition,
                                                secret_columns, index_usage_summary, index_size_summary )