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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16
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3answers
25k views

Efficient INSERT INTO a Table With Clustered Index

I have a SQL statement that inserts rows into a table with a clustered index on the column TRACKING_NUMBER. E.G.: INSERT INTO TABL_NAME (TRACKING_NUMBER, COLB, COLC) SELECT TRACKING_NUMBER, COL_B, ...
16
votes
2answers
4k views

Index vs. partition

Why is it not possible to achieve performance improvements with indexes only, so that other techniques like table partitioning becomes necessary? The question relates only to performance, of course ...
16
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2answers
43k views

MySQL creates temporary tables on disk. How do I stop it?

We are running a site (Moodle) that the users currently find slow. I think I have tracked down the problem to MySQL creating temporary tables on disk. I watch the variable created_tmp_disk_tables in ...
16
votes
2answers
3k views

Why does DELETE leave a lingering effect on performance?

At the end is a test script for comparing the performance between a @table variable and a #temp table. I think I've set it up correctly - the performance timings are taken outside of the DELETE/...
16
votes
3answers
6k views

Is the overhead of frequent query cache invalidation ever worth it?

I'm currently working on a MySQL database where we are seeing a large number of invalidations from the query cache, primarily because of the high number of INSERT, DELETE and UPDATE statements that ...
16
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5answers
17k views

What's better for large changes to a table: DELETE and INSERT every time or UPDATE existing?

I am making a project where I need to change around 36K records in one table daily. I'm wondering what will perform better: delete rows and insert new ones, or update already existing rows For me ...
15
votes
5answers
14k views

Does restarting SQL Server speed it up?

I have noticed that some DBAs restart SQL Server very frequently, sometimes even nightly. I believe they do it to free up some memory, or perhaps to speed up queries too. I know that after a restart ...
15
votes
3answers
8k views

Does “WHERE 1=1” usually have an impact on query performance?

I recently saw the question "where 1=1 statement"; a SQL construct I have used often in constructing dynamic SQL in an effort to write cleaner code (from the perspective of the host language). ...
15
votes
2answers
12k views

How badly do SQL Compilations impact the performance of SQL Server?

I am profiling an instance of a SQL Server 2005 and I, via PerfMon's SQLServer:SQL Statistics - SQL Compilations/sec metric, I see that the average is about 170 or so. I whipped out SQL Profiler ...
15
votes
1answer
2k views

Best way to write SQL Query that checks a column for non-NULL value or NULL

I have a SP with a parameter that has NULL as default value and then I want to do a query like this: SELECT ... FROM ... WHERE a.Blah = @Blah AND (a.VersionId = @VersionId OR (@VersionId IS NULL AND ...
15
votes
7answers
406 views

Which of these table designs is better for performance?

I have been asked to create something which tracks the daily cost to collect on accounts, and I am trying to figure out a database table schema that would support this. Here's what I know Company ...
15
votes
2answers
6k views

How to create an index to speed up an aggregate LIKE query on an expression?

I may be asking the wrong question in the title. Here are the facts: My customer service folk have been complaining about slow response times when doing customer lookups on the administration ...
15
votes
3answers
14k views

How to optimization database for heavy I/O from updates (software and hardware)

The situation I have a postgresql 9.2 database which is quite heavily updated all the time. The system is hence I/O bound, and I'm currently considering making another upgrade, I just need some ...
15
votes
1answer
12k views

Index optimization with dates

I have a large table of objects (15M+ row) in PostgreSQL 9.0.8, for which I want to query for outdated field. I want to divide the query by millions, for scalability & concurrency purposes, and I ...
15
votes
2answers
2k views

Does varchar size matter in temporary tables?

There is a debate at my wife's work about just using varchar(255) for all varchar fields in temporary tables in stored procedures. Basically, one camp wants to use 255 because it will always work ...
14
votes
10answers
1k views

What are the top 3 performance Issues that you encounter with your SQL Servers?

I am a student from Fontys University in Eindhoven, and I am currently carrying out a series of interviews to help with the development of a SQL Server tool and I would like to get feedback from the ...
14
votes
5answers
507 views

Indexing from start or when performance problem arises?

My question is regarding use of indexes. Should I start indexing right from the start or when performance problem arises? We can also create temporary index while executing a query. What are the ...
14
votes
4answers
1k views

The order of columns in a table [duplicate]

From what I've seen so far, when we define a table, normally we put the primary key as the first column. If there are miscellaneous columns that are common in all tables, they come at the bottom of ...
14
votes
3answers
10k 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? Edit: Not a dupe of Would ...
14
votes
2answers
35k views

What is the fastest way to insert large numbers of rows?

I have a database where I load files into a staging table, from this staging table i have 1-2 joins to resolve some foreign keys and then insert this rows into the final table (which has one partition ...
14
votes
5answers
15k views

Why using innodb_file_per_table?

There are many articles exaggerating (IMHO of course) the need for innodb_file_per_table. I understand that with innodb_file_per_table, there should be a better control over the individual tables; ...
14
votes
3answers
2k views

Is there any point in undersizing VARCHAR columns?

Googling around there seems to be mixed reports whether the size of a VARCHAR2 column in Oracle impacts performance or not. I would like to give the question of VARCHAR size a little twist and hope ...
14
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2answers
400 views

LOB_DATA, slow table scans, and some I/O questions

I have a rather big table with one of the columns being an XML data with an average size of XML entry being ~15 kilobytes. All other columns are regular ints, bigints, GUIDs etc. To have some concrete ...
14
votes
2answers
6k views

Reasons for occasionally slow queries?

We are running MySQL 5.1 on Windows Server 2008 R2. We have been doing some diagnostics on our database of late and have found some disturbing artifacts which we can't explain. We added some code to ...
14
votes
8answers
20k views

Tools to monitor Oracle Database Performance on Standard Edition

Here is what I am looking for: Works on Standard Edition i.e. No Diagnostic Pack. Provides both current and historical performance data. Good visuals for easy spotting of trends and presentation ...
13
votes
1answer
2k 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 ...
13
votes
6answers
29k views

SQL Server 2012 slower than 2008

I migrated a large website and database from an older server (Windows 2008 / SQL Server 2008 / 16 GB RAM / 2 x 2.5 GHz Quad Core / SAS disks) to a newer, much better server (Windows 2008 R2 / SQL ...
13
votes
3answers
3k views

Slow deletion of records when a trigger is enabled

Thought this was solved with the link below - the work around works - but the patch doesn't. Working with Microsoft support to resolve. http://support.microsoft.com/kb/2606883 Ok so I have an ...
13
votes
2answers
162 views

Index on a persisted computed column not seekable?

I have table, called Address, that has a persisted computed column called Hashkey. The column is deterministic but not precise. It has a unique index on it that is not seekable. If I run this query, ...
13
votes
2answers
14k views

Order by column should have index or not?

I have added indexes to table which are used for searching result. I am showing results by ASC or DESC order. So that column should have index or not? I have 2 more indexes on that table. How ...
12
votes
4answers
5k views

Is it possible to increase query performance on a narrow table with millions of rows?

I have a query that is currently taking an average of 2500ms to complete. My table is very narrow, but there are 44 million rows. What options do I have to improve performance, or is this as good as ...
12
votes
3answers
6k views

SQL Server - Temporary vs. Physical Tables

A movement is afoot in my place of employ to move away from using #temp tables and instead to use permanent physical tables with SPIDs. Whenever one would have previously INSERTed INTO a #temp table, ...
12
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3answers
6k views

How do indices impact query performance?

Obviously keeping several different indices has a negative impact on insert and delete performance. How about query performance: Does it make sense at all keeping too many indices on a table? Will the ...
12
votes
2answers
1k views

Postgres query plan of a UDF invocation written in pgpsql

It's possible when using the pgadmin or plsql to get a hold of a query plan for a sql statement executed via a UDF (using EXPLAIN). So, how do I get a hold of the query plan for a particular ...
12
votes
3answers
11k views

Best of MyISAM and InnoDB

Is it possible to make InnoDB to use indexes same as MyISAM instead of clustered index due to limitation of RAM while getting benefit of its concurrency performance?
12
votes
4answers
14k views

Mysql int vs varchar as primary key (InnoDB Storage Engine?

I am build a web application (project management system) and I have been wondering about this when it come to performance. I have an Issues table an inside it there are 12 foreign keys linking to ...
12
votes
2answers
10k views

Percona vs MySQL

What is Percona? How does it differ from MySQL? When should we consider switching (or upgrading) from stock MySQL to Percona? To add some specifics in our situation we almost exclusively use ...
12
votes
6answers
28k views

Fastest way to check if InnoDB table has changed

My application is very database intensive. Currently, I'm running MySQL 5.5.19 and using MyISAM, but I'm in the process of migrating to InnoDB. The only problem left is checksum performance. My ...
12
votes
2answers
243 views

How to track blocking that happen for less than a second - SQL Server

I am trying to troubleshoot a blocking issue which happens for less than a second. The OLTP application is very sensitive and has to have an response time of less than 200ms for some transactions as ...
12
votes
1answer
377 views

Why does referencing a variable in a join predicate force nested loops?

I came across this issue recently and couldn't find any discussion of it online. The query below DECLARE @S VARCHAR(1) = ''; WITH T AS (SELECT name + @S AS name2, * ...
12
votes
1answer
3k views

Optimising BCP performance for BLOB data

I'm the process of planning the live migration of a 2TB database to partitioned tables. The system is broadly speaking a document store, the majority of the space being allocated to LOBs of between ...
12
votes
1answer
5k views

How to determine if there are [idle connections with] uncommitted transactions in PostgreSQL?

According to a comment on this question I asked about idle connections in PostgreSQL 9.2, some uncommitted transactions (possibly related to some of those idle connections) might cause some ...
12
votes
2answers
7k views

INSERT performance difference between temporary tables and table variable

I have the following issue in SQL Server 2005: trying to inserts some rows into a table variable takes a lot of time compared to the same insert using a temporary table. This is the code to insert ...
12
votes
2answers
2k views

SQL Server: Has anyone used the large-page allocations tuning option?

Has anyone used the tuning option of using TF834 large page allocations. I was just reading an MS article on it and was wondering if anybody had used it and seen performance gains. Are there any ...
12
votes
4answers
12k views

SQL Server statements intermittently slow on SQL Server 2008 R2

On one of our customers, we've been having some performance issues on our application. It's a .NET 3.5 web app that is consuming and updating data on a SQL Server database. Currently our production ...
12
votes
1answer
240 views

What are the performance implications of polymodels versus normal BigTable models in google app engine?

What produces the best performance in regular google app engine use, a polymodel or a normal "BigTable" model? The polymodel, effectively, creates a column in the parent table called "class" which ...
12
votes
2answers
422 views

Minimizing Indexed Reads with Complex Criteria

I'm optimizing a Firebird 2.5 database of work tickets. They're stored in a table declared as such: CREATE TABLE TICKETS ( TICKET_ID id PRIMARY KEY, JOB_ID id, ACTION_ID id, STATUS str256 ...
11
votes
2answers
20k views

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 ...
11
votes
3answers
11k views

general memory requirements for sql server 2008 r2

I'm not experienced with DBA work, but I'm trying to make a case for requesting additional resources for our sql server and was hoping I could get some smart folks to provide a rough rough estimate of ...
11
votes
3answers
7k views

SQL Server performance sudden degradation

I have a SQL Server 2005 that has become unpredictable of late, and I'm scratching my head as to why. Queries that executed in seconds are changing plans and taking minutes (taking the time in full ...