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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Select statement takes long remotely due to long “client processing time”, but short locally

While connected to our production server (SQL2008. very powerful machine), this select statement takes 2 seconds, spitting back all fields (4 MB of data in total). select top 30000 * from person ...
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2answers
1k views

PostgreSQL: reuse of complex intermediate result in same query

Using PostgreSQL (8.4), I'm creating a view that summarizes various results from a few tables (e.g creating columns a, b, c in the view), and then I need to combine some of these results together in ...
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1answer
250 views

T-SQL - OPTION (FAST x) and trace flag 8722

I have searched a long time and still haven't found the answer to my problem. Our Dynamics AX is generating queries with the query hint OPTION (FAST x), which sometimes forces a bad execution plan to ...
7
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1answer
233 views

Auto Update Statistics Duration and Interruptions

Our production SQL Server 2008 R2 sometimes begins to perform slowly: all queries begin to work too slow (and sometimes all queries just hang and wait something then continue). This usually lasts ...
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1answer
14k views

High Buffer I/O SQL Server 2008 R2 causes?

Am trying to troubleshoot performance on an SQL server that we have for our document management server and today performance has hit an all time low. Looking at the MDW I setup recently I can see a ...
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1answer
4k views

Capabilities of InnoDB INSERT Performance

Hi I am running the most recent version of Percona Server. Server version: 5.5.24-55 Percona Server (GPL), Release 26.0 I have a 10 cpu box of these characteristics. processor : 0 vendor_id ...
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2answers
256 views

High rise in SQL Server CPU after adding a DB

I have just added a "new" DB to my Server (2005), I have restored from a dead SQL2000 server to my active one (2005), and changed the compatibility to 90 (SQL Server 2005). My average CPU was on 48% ...
7
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1answer
8k views

Auto Update Statistics in SQL Server 2008R2: Why do some statistics remain stale despite a large number of row inserts?

During investigation of a slow query it appeared that the execution plan was exceptionally suboptimal (A nested loop performing 9 million executions of a seek where the estimated number of executions ...
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1answer
1k views

Database design for handling 1 billion rows and counting

We receive real-time GPS data at a rate of around 5000 pr. minute (from 4 TCP servers). Each server uses a single connection to insert the data, and buffers data in between inserts. Every 15 minutes ...
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1answer
7k views

MongoDB performance vs. PostgreSQL with 5.5 million rows / documents

Can someone help me compare these queries and explain why the PostgreSQL query executes in just under 2000ms and the MongoDB aggregate query takes almost 9000ms and sometimes as high as 130K ms? ...
7
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1answer
421 views

Strange behaviour DBCC Shrinkfile

I am attempting to run a dbcc shrinkfile in chunks of 1GB against a database where 95% of the data has been archived and deleted. I'm leaft with a 235GB file where 9GB is data/indexes. I want to ...
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1answer
107 views

Is there a performance hit by breaking out tables into different schemas in SQL Server?

Is there any kind of performance hit when querying by placing tables in different schemas in SQL Server. For instance if I had 2 tables, Table1 and Table2, and put Table1 into the test schema and ...
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1answer
325 views

Could Stack Overflow run on SQL Server Web Edition?

I am starting a new web venture that may need to scale to a high number of users. I am confident with the SPLA licencing for SQL Server Web edition, but want to know if I will need to factor in ...
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2answers
5k views

Performance of a Trigger vs Stored Procedure in MySQL

A post here on DBA.StackExchange (What are the best practices for triggers to maintain a revision number on records?) has spawned an interesting question (at least, interesting to me) regarding ...
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1answer
2k views

Recursive CTE performance

Need help with recursive CTE performance. Below CTE is running very slow as it is trying to pull heirarchical data recusively. Table is big with every root id having upto 3 recursive itemid. There ...
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3answers
2k views

Performance issue with xpath in SQL Server 2008

I have a table with lots of large xml-documents. When I run xpath expressions to select data from those documents I run into a peculiar performance issue. My query is SELECT p.n.value('.', 'int') ...
7
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2answers
407 views

Should I nest dependent outer joins in SQL Server?

I have heard mixed information on this and am hoping for a canonical or expert opinion. If I have multiple LEFT OUTER JOINs , each dependent on the last, is it better to nest them? For a contrived ...
7
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1answer
185 views

Start/Stop MySQL

I'm seeking help to understand what happens when the following command line is executed: root@prodn$ service mysqld stop Yes, it shuts down the MySQL server so access to it is no longer available ...
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2answers
23k views

SELECTing multiple columns through a subquery

I am trying to SELECT 2 columns from the subquery in the following query, but unable to do so. Tried creating alias table, but still couldn't get them. SELECT DISTINCT petid, userid, (SELECT ...
7
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1answer
212 views

What is the expected performance impact when dropping a large table

I have a 100G+ innodb table that needs to be dropped in a production environment. I am trying to do this without interruption to service. The table is no longer being written to, and needs to be ...
7
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2answers
1k views

Investigate peak in MySQL throughput

Recently one of our servers has ran out of memory and crashed. After reviewing the munin graphs, it appears that the only metric (other than memory usage) that peaked just before the crash was the ...
7
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1answer
153 views

Lower performance on newest servers

We have several db servers on production, 4 of them with very similar hardware configuration. Dell PowerEdge R620, only difference is that 2 newest ones (bought and configured 3 months ago) have RAID ...
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0answers
980 views

SQL Server 2012 performance issues (maybe due to linked server) [closed]

Summary of the problem We've spit our one database server environment into two servers. We are now having intermittent performance issues I am hoping someone can offer clues - perhaps direction ...
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3answers
5k views

Should I add an arbitrary length limit to VARCHAR columns?

According to PostgreSQL's docs, there's no performance difference between VARCHAR, VARCHAR(n) and TEXT. Should I add an arbitrary length limit to a name or address column?
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5answers
945 views

Performance tuning a Great Circle distance calculation

I have a query that I am using to find locations that are within 1km of a known point. To do this, I am using the Spherical Law of Cosines formula with my latitude and longitudes. Currently, the ...
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5answers
5k views

Improve sort performance in PostgreSQL?

I've got a simple blog database in postgres-8.4 which has two tables, articles and comments. I have a query (generated by Django) that wants to get the latest article of type 'NEWS' and also find the ...
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1answer
605 views

Would index lookup be noticeably faster with char vs varchar when all values are 36 chars

I have a legacy schema (disclaimer!) that uses a hash-based generated id for the primary key for all tables (there are many). An example of such an id is: 922475bb-ad93-43ee-9487-d2671b886479 There ...
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3answers
2k views

Query performance degrades with time and use

I have been fighting a problem for several weeks now where the performance of my SQL Server queries degrade over a few days of use. In addition every few days, a query will simply not return from my ...
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3answers
302 views

Things to consider with a bigger table

I have a table that has around 12 billion rows (row size 32 B) which grows each month by 300 million rows. I have setup partitions for each month and each month has 8 data files (since I currently ...
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4answers
40k views

High CPU usage on SQL server - Slow queries [closed]

Our MS SQL Server is using about 95% of the CPU-power. After a server (hardware) restart, or a SQL-Service restart, the usage is 0% and slowly increases over the course of 1-3 days. Depending on how ...
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votes
2answers
5k views

Configuring PostgreSQL for read performance

Our system write a lots of data (kind of Big Data system). The write performance is good enough for our needs but the read performance is really too slow. The primary key (constraint) structure is ...
6
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2answers
598 views

Index fragmentation and SSD disks

I'm new to performance problems, but I saw some discussion that SSD disks solve performance problems caused by index fragmentation. Has anyone experienced this? I'm thinking of changing my hardware ...
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2answers
736 views

What are the pros/cons of splitting date and time into separate fields vs. using the datetime data type and storing the date in a single field?

My database is extremely large and growing at a rate of ~20m rows/day. I have timestamp data that is important but most of the reporting is based on date ranges and week over week or month over month ...
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3answers
4k views

Too Many Connections

I'm using MATLAB to feed the database but after a time I'm getting a too many connections error. I always using opendb and closedb in pair. Is it to fast the feeding? Do I have to wait after I ...
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3answers
1k views

Performance of Inline-TVF vs. Views

I have a database where i am using inline TVFs (table value functions) instead of views. For example, I might have two tables called [car model] and [car manufacturer] that I'm joining together ...
6
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3answers
3k views

Is MariaDB a suitable drop in replacement for MySQL on a standard LAMP stack?

I've been wondering lately what (if any) are the improvements available in MariaDB over 'conventional' MySQL? I understand that where platform interoperability and/or backwards compatibility may be ...
6
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3answers
303 views

Query performance

Why SELECT Barraportfolioname FROM portfolio WHERE id IN (SELECT DISTINCT i1.portfolioid FROM Import i1 LEFT OUTER JOIN Import i2 ON ...
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4answers
361 views

What are the performance implications of running multiple smaller DBs instead of a single larger DB on a server?

Our database architecture allows multiple 'customers' to exist in the same database, yet we split them into mulitple database for administrative reasons [patching, backup, etc.] Question 1 What ...
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4answers
1k views

When to use MySQL query_cache?

Up until recently, I have viewed the query cache as a very important tool to improve query performance. Today, I was listening to a podcast that discussed tuning the query cache to 0, and using a ...
6
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1answer
3k views

How to improve Procedure Cache Hit Ratio?

From what I can tell Procedure Cache Hit Ratio below 95% is a problem. On my box, the values hover from 85 to 95%. How do I fix this issue? The server seems to have plenty of RAM so that ...
6
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2answers
2k views

Why use separate databases for high traffic/volume tables?

While looking at the database structure of an application I am using I recognized that it uses 3 different databases on the same SQL Server instance for different things. The first one contains the ...
6
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2answers
7k views

SQL query slow-down from 1 second to 11 minutes - why?

Question: I'm porting the below query (listing tables by foreign key dependencies) to PostGreSql. WITH Fkeys AS ( SELECT DISTINCT OnTable = OnTable.name ,AgainstTable = ...
6
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4answers
917 views

Four db servers all identical, one is much slower than the others

The setup We have an application loading a lot of transaction data for later querying. It's sharded on 4 SQL Server 2008R2 Enterprise Edition on Windows Server 2008 64 bits. All servers are ...
6
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2answers
2k views

Rebuilding index has impact on mdf/ldf files SQL Server 2008

While rebuilding index have used option 'SORT_IN_TEMPDB = ON' in order to avoid unnecessary growing your user database files. What does it exactly means? Is complete process done on TempDB and does ...
6
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4answers
844 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
816 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
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1answer
872 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 ...
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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 ...
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2answers
1k 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 ...