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The answer I have found here is when statistics are expired and not when they are automatically updated.
I need your help here to answer when they are updated.
When I was recently working on the course, “Should Developers Manage Index Maintenance?
” I explained that in my experience, statistics maintenance can make more of a difference to performance than index maintenance can.
I also noted that one of the big “maintenance goofs” that I’ve made in the past is to be overly eager to update statistics. Here’s some detail on why doing that can be so slow, and how it can eat up more resources than you might think.
(This is a long one, so scroll on down to the end of the post for a list of spoilers, if you like.) When people manually update statistics, they generally don’t update just a single column stats, or stats for a single index.
You should update statistics on the geodatabase system tables after many new tables or feature classes have been added to the geodatabase, a large number of versioned edits have been performed, or the geodatabase has been compressed.# Name: Analyze # Description: analyzes all datasets in an enterprise geodatabase # for a given user.
I searched the Internet as well many official MS documents in order to find answers.
” The obvious way to do that it to tell SQL Server to do more than just take a sample of the data: instead to do it with FULLSCAN.
So they use a command like this: of extra IO to the work of updating statistics. It has only six statistics on it: I queried information about them with a query like this.
But it chose to use the clustered index.) Next, SQL Server went to work on the Fake Birth Date Stamp column statistic. SELECT Stat Man([SC0]) FROM (SELECT TOP 100 PERCENT [Fake Birth Date Stamp] AS [SC0] FROM [dbo].[First Name By Birth Date_1966_2015] WITH (READUNCOMMITTED) ORDER BY [SC0] ) AS _MS_UPDSTATS_TBL OPTION (MAXDOP 4) Here is the plan it used to get the data to update the column statistic: This time, SQL Server chose to scan the nonclustered index on First Name Id. But we haven’t actually updated its statistic yet, so… Look on the bright side: it may be the third time we’ve scanned this nonclustered index, but at least this time we didn’t have any tempdb spills.
Looking at the properties of the scan, it figured out that Fake Birth Date Stamp would be there (because of the clustering key), and decided to scan this nonclustered index and output just that column: But … We didn’t allocate enough memory for our sort and had a little spill in tempdb. I don’t have a non-clustered index on this column for SQL Server to scan, but I was surprised that it wanted to re-compute every single row for it, because I mark this column as ‘persisted’ (I double-checked with a query). We’ve got another nonclustered index, and it has two key columns.
Permanent table If the table has no rows, statistics is updated when there is a single change in table.