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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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 ...
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Qcache_free_memory not full yet I get alot of Qcache_lowmem_prunes

I just started dabbling with the query cache for our CMS. Can anyone tell me (or at least give a good guess) why I get a lot of Qcache_lowmem_prunes when more than half of Qcache_free_memory is free? ...
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Performance Hit using CAST() in TSQL (SQL Server)?

We have a SQL generator that emits SQL conditional statements generically for specified fields (which for the sake of discussion: we will label as myField). So, if myField is of type NVARCHAR, we ...
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TSQL: Find Queries causing too many SQL Compilations and SQL ReCompilations seperately

I want to find out what is causing the high SQL Compilations (not re-compilations) I am seeing in performance monitor counters. Here is my take on it: If I am seeing a lot of SQl compilations, then ...
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What can I add to a server to make SQL restores faster?

I have a 2.8TB SQL database (mostly data files, some 400GB of log files) that currently takes around 9 hours to restore. This database is used for testing purposes and must be deleted and restored ...
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Displaying query plans in Server Management Studio

Another SQL server question: I have a simple query that gives me the most CPU intensive SQL since the counters were reset: select top 10 sum(qs.total_worker_time) as total_cpu_time, ...
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199 views

Is there a performance gain by handling data with stored procedures versus feeding it into functions after retrieval?

Title sums it up. I'm reasonably well off with PHP, and comfortable getting it to do what I need it to with values pulled from MySQL, however in the interest of expanding my knowledge I've been ...
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152 views

Why is TOP operation in SQL execution plan

After searching for a while, I decided to post this question for lack of finding an answer and apologize if there is a similar question/answer out there. When running the query below on two similarly ...
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183 views

Poor cardinality estimate disqualifies INSERT from minimal logging?

Why is the second INSERT statement ~5x slower than the first? From the amount of log data generated, I think that the second is not qualifying for minimal logging. However, the documentation in the ...
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How to boost performance of virgin queries in MS SQL Server?

I have ASP.NET web site that does it's own independent caching of data and data does not change for long periods of time, so it does not need to query SQL Server second time with same query. I need to ...
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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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Multiple Oracle Instances — is this a good practice?

One of my clients has deployed our product's db into a Solaris machine which already has 3 instances of Oracle. So, right now there are 4 instances of Oracle running on the same machine. And now we're ...
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430 views

Why would MySQL do serial synchronous I/O?

When looking at a particularly annoying query over MyISAM tables which takes a long time to execute on a number of occasions, I have noted that MySQL seems to expose a rather strange I/O pattern: when ...
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IO_STALL question and understanding

I am collecting IO_STALLS from sys.dm_io_virtual_file_stats every 5minutes and then doing a delta to see which files are being affected most by IO. In one 5min period I get a delta of 5826331 ms ...
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2answers
3k views

Why you want to avoid Dynamic SQL in stored procedure?

I have heard one said you do not want to use Dynamic SQL. Can you give some concrete example or real-life example? Personally, I code it a few times in my database. I think it is OK because it's ...
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830 views

Pros and Cons of Checking if value exist for unique column or let db raise unique error on inserting

While writing a query other day a thought came to me and have stuck in my mind. What is preferable, first checking if a value for a unique column exists and then inserting or insert and let db raise ...
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Is ASYNC_NETWORK_IO wait type anything to worry about?

In looking at the list of sprocs that take long time to execute, one stands out as causing the most wait. However, most of that wait (81%) is ASYNC_NETWORK_IO and I know why: the sproc transfers ...
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MySQL LOAD DATA INFILE slows by 80% after a few gigs of input with InnoDB engine

I'm loading a 100GB file via LOAD DATA INFILE. I've had good success with MyISAM, a few hours and done. I'm trying it now using InnoDB. The load starts fast at over 10MB/sec (watching the table file ...
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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 ...
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2answers
2k 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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21k views

SQL Server 2008 R2 high Buffer I/O causes

Am trying to troubleshoot performance on a SQL Server that we have for our document management server and today performance has hit an all time low. Looking at the Management Data Warehouse (MDW) I ...
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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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226 views

Application querying empty tables

My company uses an application which has pretty major performance issues. There are a number of problems with the database itself which I am in the process of working through, but many of the problems ...
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2answers
17k views

High CXPACKET and LATCH_EX waits

I am having some performance issues with a data processing system which I am working on. I have gathered wait stats from a one hour peroid which show a large amount of CXPACKET and LATCH_EX wait ...
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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? ...
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What is the usage of performance_schema in MySQL 5.5?

I have upgraded to MySQL version 5.5. There, I had observed performance_schema in the schema list. What is the usage of this new schema..? How can we monitor using this schema..? What are the ...
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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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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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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 ...
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41k 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 ...
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1answer
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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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In Google App Engine, what is the most effective many-to-many join model?

The BigTable design rejects many of the philosophies of standard relational models, explicitly preferring denormalization to a big host of tiny tables. One of the larger areas where this is a problem ...
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567 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 ...
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1answer
215 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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1answer
226 views

To partition or not to partition?

Having already read several questions on SO, external blog posts and manual SO: Foreign Key constraint to partitioned table in Pg dba.SE: Different ways of handling FK to partitioned table in Pg ...
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158 views

Which to trust?

We are troubleshooting a long-running issue with a vendor. Their software has a tendency to freeze up and stop working once or twice a week causing major disruptions to our operation. They have been ...
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1answer
186 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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4answers
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At What Point Should I Split or Partition a Very Large but Simple Table

Our site has some large but simple (INT, INT, DATE) tables for stats. Each table has up to 300,000,000 rows, and gets bigger every day. The hosting provider has suggested that we split or partition ...
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4answers
937 views

DDL contention on TempDB

I have a SQL Server 2005 Standard x64 that is experiencing issues with TempDB DDL contention for the past few months. The server will experiencing contention on wait resource 2:1:103 (the wait type ...
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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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833 views

More Databases Per Sql Server 2005 Instance

Our company currently hosts about 400 databases per SQL Server 2005 instance. 500-600 databases and we see performance start to deteriorate. Database size ranges from 50mb to 40-60gb in the extreme, ...
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3answers
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Performance benefit of taking unused databases offline

I have several databases for legacy applications which run in VMs that are currently off until someone needs to look at some history. I have set each of the databases used by these applications to ...
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3answers
3k 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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2answers
882 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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2answers
4k views

Index on primary key not used in simple join

I have the following table and index definitions: CREATE TABLE munkalap ( munkalap_id serial PRIMARY KEY, ... ); CREATE TABLE munkalap_lepes ( munkalap_lepes_id serial PRIMARY KEY, ...
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2answers
12k 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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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 ...
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922 views

Fast reads without paying the price on writes

We have a large append-only table containing financial transactions. On average 1000 transactions are inserted per minute. Since there are now more and more usecases where we actually want to read, ...
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What is faster, one big query or many small queries?

I have been working for different companies, and I have noticed that some of them prefer to have views that will join a table with all its "relatives". But then on the application some times, we only ...
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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 ...