SQL Server Optimize Large Changing Table - sql-server

I have reports that perform some time consuming data calculations for each user in my database, and the result is 10 to 20 calculated new records for each user. To improve report responsiveness, a nightly job was created to run the calculations and dump the results to a snapshot table in the database. It only runs for active users.
So with 50k users, 30k of which are active, the job "updates" 300k to 600k records in the large snapshot table. The method it currently uses is it deletes all previous records for a given user, then inserts the new set. There is no PK on the table, only a business key is used to group the sets of data.
So my question is, when removing and adding up to 600k records every night, are there techniques to optimize the table to handle this? For instance, since the data can be recreated on demand, is there a way to disable logging for the table as these changes are made?
UPDATE:
One issue is I cannot do this in batch because the way the script works, it's examining one user at a time, so it looks at a user, deletes the previous 10-20 records, and inserts a new set of 10-20 records. It does this over and over. I am worried that the transaction log will run out of space or other performance issues could occur. I would like to configure the table to now worry about data preservation or other items that could slow it down. I cannot drop the indexes and all that because people are accessing the table concurrently to it being updated.

It's also worth noting that indexing could potentially speed up this bulk update rather than slow it down, because UPDATE and DELETE statements still need to be able to locate the affected rows in the first place, and without appropriate indexes it will resort to table scans.
I would, at the very least, consider a non-clustered index on the column(s) that identify the user, and (assuming you are using 2008) consider the MERGE statement, which can definitely avoid the shortcomings of the mass DELETE/INSERT method currently employed.
According to The Data Loading Performance Guide (MSDN), MERGE is minimally logged for inserts with the use of a trace flag.
I won't say too much more until I know which version of SQL Server you are using.

This is called Bulk Insert, you have to drop all indexes in destination table and send insert commands in large packs (hundreds of insert statements) separated by ;
Another way is to use BULK INSERT statement http://msdn.microsoft.com/en-us/library/ms188365.aspx
but it involves dumping data to file.
See also: Bulk Insert Sql Server millions of record

It really depends upon many things
speed of your machine
size of the records being processed
network speed
etc.
Generally it is quicker to add records to a "heap" or an un-indexed table. So dropping all of your indexes and re-creating them after the load may improve your performance.
Partitioning the table may see performance benefits if you partition by active and inactive users (although the data set may be a little small for this)
Ensure you test how long each tweak adds or reduces your load and work from there.

Related

Find out the recently selected rows from a Oracle table and can I update a LAST_ACCESSED column whenever the table is accessed

I have a database table which have more than 1 million records uniquely identified by a GUID column. I want to find out which of these record or rows was selected or retrieved in the last 5 years. The select query can happen from multiple places. Sometimes the row will be returned as a single row. Sometimes it will be part of a set of rows. there is select query that does the fetching from a jdbc connection from a java code. Also a SQL procedure also fetches data from the table.
My intention is to clean up a database table.I want to delete all rows which was never used( retrieved via select query) in last 5 years.
Does oracle DB have any inbuild meta data which can give me this information.
My alternative solution was to add a column LAST_ACCESSED and update this column whenever I select a row from this table. But this operation is a costly operation for me based on time taken for the whole process. Atleast 1000 - 10000 records will be selected from the table for a single operation. Is there any efficient way to do this rather than updating table after reading it. Mine is a multi threaded application. so update such large data set may result in deadlocks or large waiting period for the next read query.
Any elegant solution to this problem?
Oracle Database 12c introduced a new feature called Automatic Data Optimization that brings you Heat Maps to track table access (modifications as well as read operations). Careful, the feature is currently to be licensed under the Advanced Compression Option or In-Memory Option.
Heat Maps track whenever a database block has been modified or whenever a segment, i.e. a table or table partition, has been accessed. It does not track select operations per individual row, neither per individual block level because the overhead would be too heavy (data is generally often and concurrently read, having to keep a counter for each row would quickly become a very costly operation). However, if you have you data partitioned by date, e.g. create a new partition for every day, you can over time easily determine which days are still read and which ones can be archived or purged. Also Partitioning is an option that needs to be licensed.
Once you have reached that conclusion you can then either use In-Database Archiving to mark rows as archived or just go ahead and purge the rows. If you happen to have the data partitioned you can do easy DROP PARTITION operations to purge one or many partitions rather than having to do conventional DELETE statements.
I couldn't use any inbuild solutions. i tried below solutions
1)DB audit feature for select statements.
2)adding a trigger to update a date column whenever a select query is executed on the table.
Both were discarded. Audit uses up a lot of space and have performance hit. Similary trigger also had performance hit.
Finally i resolved the issue by maintaining a separate table were entries older than 5 years that are still used or selected in a query are inserted. While deleting I cross check this table and avoid deleting entries present in this table.

Best way to handle updates on a table

I am looking for much more better way to update tables using SSIS. Specifically, i wanted to optimize the updates on tables (around 10 tables uses same logic).
The logic is,
Select the source data from staging then inserts into physical temp table in the DW (i.e TMP_Tbl)
Update all data matching by customerId column from TMP_Tbl to MyTbl.
Inserts all non-existing customerId column from TMP_Tbl1 to MyTbl.
Using the above steps, this takes some time populating TMP_Tbl. Hence, i planned to change the logic to delete-insert but according to this:
In SQL, is UPDATE always faster than DELETE+INSERT? this would be a recipe for pain.
Given:
no index/keys used on the tables
some tables contains 5M rows, some contains 2k rows
each table update took up to 2-3 minutes, which took for about (15 to 20 minutes) all in all
these updates we're in separate sequence container simultaneously runs
Anyone knows what's the best way to use, seems like using physical temp table needs to be remove, is this normal?
With SSIS you usually BULK INSERT, not INSERT. So if you do not mind DELETE - reinserting the rows should in general outperform UPDATE.
Considering this the faster approach will be:
[Execute SQL Task] Delete all records which you need to update. (Depending on your DB design and queries, some index may help here).
[Data Flow Task] Fast load (using OLE DB Destination, Data access mode: Table of fiew - fast load) both updated and new records from source into MyTbl. No need for temp tables here.
If you cannot/don't want to DELETE records - your current approach is OK too.
You just need to fix the performance of that UPDATE query (adding an index should help). 2-3 minutes per every record updated is way too long.
If it is 2-3 minutes for updating millions of records though - then it's acceptable.
Adding the correct non-clustered index to a table should not result in "much more time on the updates".
There will be a slight overhead, but if it helps your UPDATE to seek instead of scanning a big table - it is usually well worth it.

Delete 200G ( 465025579 records ) of data from sql server

I have database with one of the tables that got over populated ( 465025579 records ), what is the best way to delete the records and keep only 3 months of the records, without the device to hang?
Delete them in batches based on date earliest first. Sure it'll take some time, but it's safer (as you are defining which to delete) and not so resource intensive. It also means you can shrink the database in batches too, instead of one big hit (which is quite resource intensive).
Yeah, it might fragment the database a little, but until you've got the actual data down to a manageable level, there isn't that much you can do.
To be fair, 200G of data isn't that much on a decent machine these days.
All this said, I'm presuming you want the database to remain 'online'
If you don't need the database to be available whilst you're doing this, the easiest thing to do is usually to select the rows that you want to keep into a different table, run a TRUNCATE on this table, and then copy the saved rows back in.
From TRUNCATE:
TRUNCATE TABLE is similar to the DELETE statement with no WHERE clause; however, TRUNCATE TABLE is faster and uses fewer system and transaction log resources.

How to do very fast inserts to SQL Server 2008

I have a project that involves recording data from a device directly into a sql table.
I do very little processing in code before writing to sql server (2008 express by the way)
typically i use the sqlhelper class's ExecuteNonQuery method and pass in a stored proc name and list of parameters that the SP expects.
This is very convenient, but i need a much faster way of doing this.
Thanks.
ExecuteNonQuery with an INSERT statement, or even a stored procedure, will get you into thousands of inserts per second range on Express. 4000-5000/sec are easily achievable, I know this for a fact.
What usually slows down individual updates is the wait time for log flush and you need to account for that. The easiest solution is to simply batch commit. Eg. commit every 1000 inserts, or every second. This will fill up the log pages and will amortize the cost of log flush wait over all the inserts in a transaction.
With batch commits you'll probably bottleneck on disk log write performance, which there is nothing you can do about it short of changing the hardware (going raid 0 stripe on log).
If you hit earlier bottlenecks (unlikely) then you can look into batching statements, ie. send one single T-SQL batch with multiple inserts on it. But this seldom pays off.
Of course, you'll need to reduce the size of your writes to a minimum, meaning reduce the width of your table to the minimally needed columns, eliminate non-clustered indexes, eliminate unneeded constraints. If possible, use a Heap instead of a clustered index, since Heap inserts are significantly faster than clustered index ones.
There is little need to use the fast insert interface (ie. SqlBulkCopy). Using ordinary INSERTS and ExecuteNoQuery on batch commits you'll exhaust the drive sequential write throughput much faster than the need to deploy bulk insert. Bulk insert is needed on fast SAN connected machines, and you mention Express so it's probably not the case. There is a perception of the contrary out there, but is simply because people don't realize that bulk insert gives them batch commit, and its the batch commit that speeds thinks up, not the bulk insert.
As with any performance test, make sure you eliminate randomness, and preallocate the database and the log, you don't want to hit db or log growth event during test measurements or during production, that is sooo amateurish.
bulk insert would be the fastest since it is minimally logged
.NET also has the SqlBulkCopy Class
Here is a good way to insert a lot of records using table variables...
...but best to limit it to 1000 records at a time because table variables are "in Memory"
In this example I will insert 2 records into a table with 3 fields -
CustID, Firstname, Lastname
--first create an In-Memory table variable with same structure
--you could also use a temporary table, but it would be slower
declare #MyTblVar table (CustID int, FName nvarchar(50), LName nvarchar(50))
insert into #MyTblVar values (100,'Joe','Bloggs')
insert into #MyTblVar values (101,'Mary','Smith')
Insert into MyCustomerTable
Select * from #MyTblVar
This is typically done by way of a BULK INSERT. Basically, you prepare a file and then issue the BULK INSERT statement and SQL Server copies all the data from the file to the table with the fast method possible.
It does have some restrictions (for example, there's no way to do "update or insert" type of behaviour if you have possibly-existing rows to update), but if you can get around those, then you're unlikely to find anything much faster.
If you mean from .NET then use SqlBulkCopy
Things that can slow inserts include indexes and reads or updates (locks) on the same table. You can speed up situations like yours by avoiding both and inserting individual transactions to a separate holding table with no indexes or other activity. Then batch the holding table to the main table a little less frequently.
It can only really go as fast as your SP will run. Ensure that the table(s) are properly indexed and if you have a clustered index, ensure that it has a narrow, unique, increasing key. Ensure that the remaining indexes and constraints (if any) do not have a lot of overhead.
You shouldn't see much overhead in the ADO.NET layer (I wouldn't necessarily use any other .NET library above SQLCommand). You may be able to use ADO.NET Async methods in order to queue several calls to the stored proc without blocking a single thread in your application (this potentially could free up more throughput than anything else - just like having multiple machines inserting into the database).
Other than that, you really need to tell us more about your requirements.

How to profile and address insert/update performance issues?

I am trying to insert thousands of rows into a table and performance is not acceptable. Rows on a particular table take 300ms per row to insert.
I know that tools exist to profile queries run against SQL Server (SQL Server Profile, Database Tuning Advisor), but how would I profile insert and update statements to determine slow running inserts? Am I forced to use perfmon while the queries run and deduce the issue with counters?
I would first check the query plan of a single insert to understand the costs associated to that operation - it is not known from the question whether the insert is selecting the data from elsewhere.
I would then check the table indexing for the following:
how many indexes are in place (apart from filtered indexes, each index will be inserted into as well)
whether a clustered index is present or are we inserting into a heap.
if the clustered index key means we will be getting a hotspot benefit on the end of the table or causing a large quantity of page splits.
This is all SQL schema based issues, assuming there is no problems within SQL, you can start checking disk IO counters to check for disk queue lengths and response time. Not forgetting the Log drive response time since each insert will be logged.
These kind of problems are very difficult to nail down as any 1 perscriptive thing / silver bullet you can give advice over, just a range of things you should be checking.
I'm betting that the problem is with the selects and not necessarily the updates. Have you tried profiling the select part of the update statement to make sure there isn't a problem there first?

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