An evaluation of whether a system works well enough to be fit for purpose. Normally performance refers to the speed with which a system completes an operation or set of operations over time.

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871 views

How can I tell if my SQL Server DB performance is hardware-limited?

Testing an app currently under single-user load - as the test data has increased to production sizes (400k-2M rows per table), some SELECT sp's are not quite fast enough anymore (with limited test ...
6
votes
2answers
842 views

Adding a Clustered index to a HEAP table on someone else's app

We're using a proprietary application based on SQL Server 2005, which has many HEAP based tables (that is, no Clustered index). Over the years, these tables have grown badly fragmented (e.g. 99% ...
6
votes
1answer
888 views

Password hashes: Fixed-length binary fields or single string field?

I'm currently having am amusing debate with a friend, and we simply can't agree on the best method to store salted passwords in a database. The two options on the table are: Storing the hash and the ...
6
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2answers
1k views

Explanation requested for slow DELETE with SQL Server

I would like to get some extra insights/reasoning for SQL Server delete behavior. We have a fairly large database of over 1800 GB. In there are some very shallow tables (only a few integer columns) ...
6
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1answer
5k views

Troubleshooting SOS_SCHEDULER_YIELD wait

Running our corporate ERP (Dynamics AX 2012), I noticed our production environment seemed much slower than our development systems. After performing the same activities in both the development and ...
6
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2answers
2k views

Slow ORDER BY with LIMIT

I have this query: SELECT * FROM location WHERE to_tsvector('simple',unaccent2("city")) @@ to_tsquery('simple',unaccent2('wroclaw')) order by displaycount I'm happy with it: "Sort ...
6
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2answers
714 views

Is it possible to give the optimizer more or all time it needs?

Given that the optimizer cannot take al the time it needs (it has to minimize the execution time and not contribute to it) to explore all possible execution plans it sometimes get cut off. I was ...
6
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2answers
244 views

Feasible to have thousands of users in Postgres?

We are creating SAAS where we will at most have 50.000 customers. We are considering creating a user in the Postgres database for each customer. We will map each user that logs into our service to a ...
6
votes
4answers
7k views

SQL Server - Separating data, log, and TempDB files on a SAN

I have a SQL Server connected to a SAN. Our new storage vendor recommends that all LUNs span the entire disk array, which is RAID5. I would normally request 3 separate LUNs (data, log, and TempDB) ...
6
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3answers
7k views

How database size affects performance: Theory vs reality

There is a lot out there that says database size should not affect performance to any great degree. As long as indexes on tables fit in memory the database should remain performant. However what is ...
6
votes
1answer
381 views

Is there a quickish, straighforward way to measure Transactions Per Second on SQL Server 2000?

The sys.dm_os_performance_counters DMV introduced in SQL Server 2005 makes this task somewhat trivial. However, my Google-Fu has been blocked in finding a way to do this in SQL Server 2000. How can ...
6
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2answers
297 views

Row padding to get more performance

I have read a document (Designing Highly Scalable OLTP Systems) that describe a trick how to get more performance: Because rows are small (many fit a page) multiple locks may compete for one ...
6
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1answer
328 views

How can I benchmark the performance of UDFs to figure out which one is faster?

Basically I have two scalar UDFs that output the same data, one that uses a cursor and one that uses a recursive CTE. I want to determine which one should be used and discard the other; I'd prefer to ...
6
votes
1answer
208 views

Does tempDB disk perf matter if you have plenty of unused memory?

We have a SQL Server 2012 Enterprise setup with a large amount of RAM (256 GB), and at this time fairly small databases (about 17GB). Right now we are experiencing performance issues due to various ...
6
votes
1answer
375 views

Sql server snapshot isolation overhead when read_committed_snapshot is enabled

When SQL Server's read committed snapshot is on (and thus some amount of row versioning is necessary), is there any additional overhead caused merely by enabling snapshot isolation? Snapshot ...
6
votes
1answer
204 views

How should we handle rows which won't be queried once they are old in PostgreSQL?

We have a table in a PostgreSQL database which is growing on the order of millions of rows per day. Each row consists of: ID Foreign user ID Date and time Other data The date and time aren't ...
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2answers
1k views

Using totals on aggregates to improve performance

I have two tables: details and totals of these details. Details (Slow solution): select OrderId = r.OrderId , TotalQty = SUM(r.Quantity) , ...
6
votes
2answers
154 views

Optimizing WHERE condition for TIMESTAMP field in MySQL SELECT statement

I am working on a schema for an analytics system which tracks usage times, and there is a need to see total usage time in a certain date range. To give a simple example, this type of query would be ...
6
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2answers
9k views

What's the difference between POINT(X,Y) and GeomFromText(“POINT(X Y)”)?

I'd like to store some geometric positions in my MySQL database. For this I use the POINT datatype. Almost everywhere I read that the function GeomFromText should be used to insert data in the table. ...
6
votes
1answer
2k views

MySQL table creation insanely slow

A simple table creation on one of my MySQL databases takes forever: mysql> CREATE TABLE blah (id BIGINT UNSIGNED NOT NULL PRIMARY KEY); Query OK, 0 rows affected (16.58 sec) The machine is quite ...
6
votes
2answers
2k views

How can I save a severely fragmented database/table?

I've recently made a discovery that might explain my slow SQL run times. I found out that the default in SSMS is to allow mdf growth of 1MB at a time. When the size of one table alone is roughly 23 ...
6
votes
1answer
4k views

Why is DELETE so much slower than SELECT, then DELETE by id?

I have a fairly busy InnoDB table (200,000 rows, I guess something like tens of queries per second). Due to a bug I got 14 rows with (the same) invalid email addresses in them and wanted to delete ...
6
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1answer
1k views

What should every DBA know? [closed]

As a SysAdmin who "wears all the hats", I find myself increasingly pulled into database projects. I took one database course back in college and since then I've always scoured resources online (like ...
6
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3answers
3k views

Why performance degradation with query hint FIRST_ROWS(1000)? [closed]

I have a query with user supplied arguments that can produce a very high amount of rows depending on the user's input. In case the user supplies very unselective arguments, the query takes a lot of ...
6
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2answers
1k views

Database locking issues?

I have run into a transaction related issue on a SQL Server 2008 production database. A brief overview is that we have a website that has numerous concurrent users around the state, who do GUI type ...
6
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1answer
90 views

Capture and Replay workload

We have a new server which we are migrating too and want to see the potential benefits of the hardware. So the idea is that we capture a workload and replay this against our new box. My question is ...
6
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2answers
27k views

way to prevent queries from waiting for table level lock

We've encountered a problem after moving the database of our customer to an extra server. This should have had positive effects on the site's performance, but there is a problem with table locking in ...
6
votes
2answers
497 views

MySQL: Does the order of the fields in a table make a difference in performance?

Specifically I am wondering if I should place all my fixed length fields like int, timestamp, char at the beginning of the CREATE TABLE and place all the variable length like varchar at the end. ...
6
votes
1answer
269 views

Timestamp-based index

I have a big database (200GB+) that contains some log info. And I want to speed up SELECT queries and stored procedures. I have a table with a GeneratedOnUtc datetime column, and have a non-clustered ...
6
votes
1answer
785 views

Huge differences of performance of MySQL in two servers

We have a MySQL server installed in two different machines, a testing server and a production server, both windows, which is used by a web application. The problem is that there are HUGE performance ...
6
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2answers
5k views

MySQL performance problem using indexed datetime column

I tried to solve the following problem for about one hour now and still didn't get any further with it. Okay, I have a table (MyISAM): ...
6
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2answers
777 views

Major Discrepancy Between SQLIO IOPS/Throughput Stats and DBCC CHECKDB Operations

I'm conducting time trials on a new SSD array running both SQLIO tests and a real-world workload of DB restores and DBCC CHECKDB calls. I'm seeing a major discrepancy between the IOPS and throughput ...
6
votes
1answer
868 views

Performance impact of sp_configure blocked process threshold change

I've been tasked with identifying any blocking happening on a production server. My plan to achieve this is to use EXECUTE sp_configure 'blocked process threshold', 5 In combination with a server ...
6
votes
1answer
355 views

Landed as BI, but databases are a big WTF, what to do?

Maybe a duplicate, but I believe my case is a bit different. From one of the answers I got to this post on SQL Server Central that also comes handy too but is not quite the same scenario: 9 Things to ...
6
votes
2answers
1k views

Transaction speed benchmarks for mySQL v5.6 replication - seems very slow

I'm trying to select the best configuration for our new infrastructure but got a bit confused about the results. I used sysbench v0.5 for the tests: prepare data sysbench ...
6
votes
1answer
1k views

Extremely Slow StatMan query issue with #SP2010 farm

The issue I’m experiencing is explained in a blog-post I created for this, (easy to refer to and to manage the responses / solutions in 1 location) which can be found here: ...
6
votes
2answers
4k views

When to make changes to the cost threshold for parallelism

While examining a performance issue , I have seen an influx on CXPACKETS suggesting I might need to look at the cost threshold for parallelism and perhaps the MAXDOP. Before making any drastic ...
6
votes
1answer
397 views

Sudden increase in log_file_sync waits

I'm on Oracle 11gR2 with a 2 node RAC system. It's shared fiber storage to an EMC Clariion. Last friday things went bad..fast. All of the sudden processes that normally ran fine for years became ...
6
votes
1answer
170 views

What is a good way to determine the performance I should expect from a PostgreSQL server?

Trying to figure out how I should expect my database to perform. Basically, I need to determine when the server I have set up is reaching its performance limits - which would help me plan server ...
6
votes
1answer
489 views

Backup to three drives suddenly slow

The situation: I have a 1.3 TB Database (SQL 2005) that I am currently backing up to 2 network shares on separate machines and on one local USB. (Don't ask why - long story involving a DBA that quit ...
6
votes
3answers
672 views

Single query sending and retreiving duplicate data on MS SQL Server?

Very odd thing happening. It would appear that all queries against a particular database in our system are periodically "running slow". Ie "normal speed" for 5 minutes then slow for 5 minutes ...
6
votes
1answer
549 views

Using an RDBMS for querying tens of Terabytes of time-series data?

I stumbled over an algorithmic / data-structures question over on SO, which I'll short quote: (...) opinions regarding best of breed data structures to be used for indexing time-series (aka ...
5
votes
3answers
409 views

Reducing the size of a database

SQL Server newbie here. I'm a MySQL guy. I'm having a look at something for a client in their 2008 SQL Server, and need some advice. Whoever designed the database chose to log insane amounts of stuff ...
5
votes
3answers
412 views

SQL Server clustered index, index balancing and insert performance using NewID

I have a large (6db) trace table. It has a clustered key (DateTime) which is created through GETDATE(). The connection pool for connections to this database/table rises as high as 50 on average ...
5
votes
2answers
2k views

Compare Microsoft SQL server performance between virtual and dedicated server

I have a dedicated windows 2008 r2 server at the moment and I am thinking about migrating to a virtual server because of the costs. Now I know that SQL should be on a dedicated server, but the ...
5
votes
2answers
391 views

How to design index for faster deletes

I want to speed up following piece of code delete from ssn_sdo where (art_id=@art_id and skl_id=@skl_id and @level=0 ) or (art_id=@art_id and skl_id=@skl_id and @level=1 and ...
5
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3answers
7k views

How can I configure MySQL Innodb to handle 1000s of inserts per hour?

I have a very high traffic website where it is possible that 1000s of new records are inserted every hour. This one error is crippling the site: PDOException: SQLSTATE[40001]: Serialization failure: ...
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3answers
1k views

Some book suggestions for performance tuning

I am in the process of improving performance on our database application. While I am not a DBA, I am pretty comfortable with SQL. I am after a book that can help me understand how queries written in ...
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3answers
668 views

SQL Server 2005 uses 1GB of RAM

Is this normal? To be exact it uses 1,068,000 KB. It occasionally shoots up to 1,400,000 if query takes too long. My total system memory is 3GB and I am running WinXP. Is there a specific amount of ...
5
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3answers
11k views

Optimizing InnoDB default settings

I looked into my.ini and saw various default settings. My database is running on a single stand-alone PC. I want to optimize the performance of InnoDB and MySQL in general for performance. There is no ...