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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Why is optimistic locking faster than pessimistic locking?

Both forms of locking cause a process to wait for a correct copy of the record if its currently in use by another process. With pessimistic locking, the lock mechanism comes from the DB itself (a ...
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1answer
7k views

Why does MySQL (InnoDB) table get faster after OPTIMIZE TABLE, but then don't work?

I have a Django web application that stores data in a MySQL InnoDB database. There is a particular page that is accessed a lot on the django admin, and the query is taking a long time (~20 seconds). ...
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2answers
2k views

How can I optimize performance on a MySQL ndbcluster?

So, this is what I have: A simple table classes__to_students: |class |student| --------------- Math Alice Math Bob Math Peter Math Anne Music Bob Music Chis Music ...
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1answer
3k views

To 'DBCC SHRINKDATABASE' or Not To 'DBCC SHRINKDATABASE': That's the question

We're freeing lots of space in a SQL Server 2008 R2 database -a Loooot! enough to care about- (we're dropping lots of unnecessary data). but the database file conserves its file size. we want to ...
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3answers
3k views

When do hash indexes become reasonable?

MySQL natively doesn't support hash indexes. So, making a pseudo hash column and creating an index on a hash column needs some thinking. And it seems to be widely understood that if the text field is ...
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585 views

Degrading PostgreSQL 8.4 write performance

Load testing of postgresql 8.4 for OLTP application suitability resulted in unpleasant situation when throughput of the database significantly degraded over time from thousands of write transactions ...
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1answer
121 views

Speeding up a GROUP BY, HAVING COUNT query

I'm trying to speed up this query in Postgres 9.4: SELECT "groupingsFrameHash", COUNT(*) AS nb FROM "public"."zrac_c1e350bb-a7fc-4f6b-9f49-92dfd1873876" GROUP BY "groupingsFrameHash" HAVING COUNT(*) ...
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1answer
154 views

How to monitor load on database server

Could anybody please suggest me a way to monitor the load on my database server? What perfmon counters should I monitor on daily basis and confirm that load on the server is increasing day by day [or] ...
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1answer
866 views

Why does this limit make the postgres planner use a much slower index scan instead of a much faster bitmap heap/index scan?

I have a table of about 700k rows in Postgres 9.3.3, which has the following structure: Columns: content_body - text publish_date - timestamp without time zone published ...
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2answers
3k views

Does using LIMIT improve the performance and is it noticeable?

I want to understand the following. Assume that I have a complicated query with let's say a join of 5 tables a group by summations and order by. Letting aside any optimizations to the query itself ...
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2answers
17k views

Index for date column for range query in Oracle?

We have a lot: select count(*) from TBL where XDATE between ? and ? and FLD = ?; We expect to boost performance by tuning index on XDATE column (which have DATE type). What type of indexes more ...
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1answer
7k views

Why is my Amazon RDS instance so slow?

I currently run a Windows Server with SQL Server Express. I'd like follow best practice and separate the application from the database, so I've created an RDS instance and exported my database. ...
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1answer
437 views

How un-clustered is a CLUSTER USING table in PostgreSQL

I have some tables which benefit greatly from CLUSTER ON/CLUSTER USING in Postgres SQL: # CLUSTER table USING index_name; # ANALYZE VERBOSE table; # CLUSTER VERBOSE; A maintenance task periodically ...
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1answer
622 views

SSD for production database

I am looking for a solution to [dramatically] improve an enterprise database performance on a system that needs to support thousands of transactions (inserts & large selects) per second. Besides ...
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4answers
7k views

mysql : inner join takes 3 minutes

I had a similar question open on SO for postgres - now having the same issue with mysql.. I have two tables - Table A : 1MM rows, AsOfDate, Id, BId (foreign key to table B) Table B : 50k rows, Id, ...
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2answers
620 views

What exactly is “pinning” in relation to indexes?

When one talks about "pinning" in indexes, what exactly is this? Is there some other word/term I can search for, as google has not provided any solutions. It is part of a test question, where ...
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4answers
19k views

Cause of High Disk Queue Length in SQL Server

I have a fairly high-throughput application that occasionally decides to collapse on me. It's not very often - about once every ~3 weeks or so. When it does, if I check out perfmon, I see 100% "Avg. ...
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3answers
502 views

SQL 2008 Developer Edition, not using all CPU´s

My SQL Server doesn´t want to use the second CPU for our Vault database. I tried to use different configurations for the CPU affinity in SQL Management Studio, but doesn't seem to fix it. I've read ...
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1answer
1k views

Oracle explain for cascading delete is wrong

My deletes in Oracle 11 are very slow. The tables are linked by foreign keys and every foreign key constraint has a delete cascade set on it. If I hit the explain button on a statement like this ...
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2answers
507 views

Using Central Management Server to provide convincing performance statistics

Central Management Server The company I work offers dedicated VMware hosted servers to its Windows clients. Among those Windows clients, there are essentially 60 single instance SQL Servers ranging ...
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1answer
4k views

I have lots of free memory. How do I use it to increase performance?

I am running Litespeed (with suExec, PHP SAPI), MySQL, DirectAdmin, named on a VPS with a 16-core Xeon CPU and 2GB RAM. Currently, only 300 MB out of 2048 are used. It might sound a stupid, but how ...
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2answers
704 views

Performance gain by moving a large table from a database and referencing with a synonym

We have SQL Server 2008 R2 database which is currently about 80Gb. About 10Gb of this is down to one table, and I wondered if there would be a performance gain if I moved this table into it's own ...
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2answers
13k views

Improve BLOB Writing Performance in Oracle 11g

I have an application that writes a lot of rows into a table that contains a blob column. The average size of the blob is 3k bytes. Is there any buffer that i can resize to improve inserts into this ...
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2answers
1k views

MySQL vs SQLite on Amazon EC2

I have a Java program and PHP website I plan to run on my Amazon EC2 instance with an EBS volume. The program writes to and reads from a database. The website only reads from the same database. On ...
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1answer
2k views

Is SQL Server Backup single or multi-threaded?

If you perform a... BACKUP DATABASE [DB_Name] TO DISK=N'c:\backups\db_name.bak' WITH STATS=10 Will that perform a single or multi-threaded write? Our Server support company advised us that if we ...
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2answers
1k views

SQL 2005- stored procedure performance troubleshooting

I am investigating performance issues for a stored procedure on SQL 2005 server. This is how I intend to do it: Analyze the stored procedure for any bad TSQL practices (like count * etc) Run it ...
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1answer
4k views

sqloledb vs sqlncli - Performance difference or just feature set?

I've been running through some Classic ASP code recently and was wondering if there was a performance difference between connecting using: ...
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2answers
190 views

IN Clause - performance difference between listing values and query

I changed this query SELECT ... FROM linkedServer.DB.Schema.Table1 t1 LEFT JOIN linkedServer.DB.Schema.Table2 t2 ON t1.ORDER_ID = t2.ORDER_ID WHERE t1.BRANCH_ID NOT IN ( '009991', '009992', ...
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3answers
92 views

Improve Restore Speed

I have a ~3GB backup file from our QA database, and a daily diff (~500MB). For data complexity reasons, some of our developers like to use regular backups from this database, and so we have a process ...
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3answers
272 views

Do I want an index if all I care to query is field not null

In SQL, do all the common considerations about indexes apply if everything I'll ever want to query (in the where condition) is when a field is not null? Is there a special configuration of the index ...
3
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2answers
101 views

Is copy/rename a good way to improve temp table performance?

An application I am working with contains this sequence of queries at the end of constructing a large temp table; I believe it is an attempt to improve performance by pruning dead tuples - create ...
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1answer
778 views

Is a clustered index on column A the same as creating a table ordered by A?

Reading the official PostgreSQL documentation for version 9.0 I read an interesting escamotage that performs better than CLUSTER for big tables: The CLUSTER command reorders the original table by ...
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1answer
3k views

What does a “Buffer cache hit ratio” of 9990 mean?

I got this query from a blog post: SELECT object_name, counter_name, cntr_value FROM sys.dm_os_performance_counters WHERE [object_name] LIKE '%Buffer Manager%' AND [counter_name] = 'Buffer cache hit ...
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2answers
272 views

SQL Server 2008 R2 Missing Index

I am performing index maintenance on a database. I have run SQL script that uses DMVs to provides a list of indexes SQL Server believes should be created. I am not creating indexes just because the ...
3
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1answer
162 views

Avoiding Deadlocks

We currently have a trigger-based system in place that does the following: When records in certain tables are modified, a trigger fires that makes a field NULL in a varying number of records in ...
3
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2answers
614 views

Autogrowth, shrink and database performance

I have already asked some questions about Autogrowth and shrink. But I have some doubts related to it. 1)I have a database which grows about 300 MB every month. So is it best to set Autogrowth of 300 ...
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4answers
10k views

Speed up large clustered index creation?

I have a large table, the row count of the table is more than 3 billion, the data space for this table is about 120 GB. And Intel Xeon CPU E5645 @2.4GHz(2 processors), 24 CPUs, 64G memory, 64bit ...
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2answers
186 views

Tablestructure for fast inserts/deletes with foreign keys

Current Situation We have a table called c with ca. 300,000 rows. In this table we store the competitors for a specific product. Example: id | competitors | some infos about competitor | ...
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1answer
2k views

Performance effects of database file size and available space

I have set the autogrowth and maxsize properties to: By 10 MB, Unlimited When I look at the Properties -> General Tab by right-clicking the database in SSMS, I see the file size is 2249MB with 6.1 ...
3
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1answer
131 views

query discrepancies on very large postgres table

I have a fairly large table (25m entries) which stores tracking data, I am not a postgres admin by trade so this may be a simple problem. these two queries although similar are taking massively ...
3
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2answers
6k views

Fast XML, slow XML

Our database update Windows application needs to transfer some data between two databases as part of the process for a certain one-time update. I chose XML as the intermediary to move the data. The ...
3
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1answer
292 views

Why are my queries getting really slow?

I own a WordPress installation, and Updated to 3.4.1. After the upgrade, I experienced a very strange slow-down. After all, I used the define('SAVEQUERIES', true); in my wp-config.php with ...
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1answer
1k views

Need advice for a 'tag' table design

My website has different content types. All content types should be tag-able (except if specified in the model, whatever). I can think of 2 options for my design: 2 tables option : 1 table for the ...
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2answers
576 views

Performance differences between executing via Linked Server vs. SSMS

We've had an issue reported where a stored procedure was behaving badly when called from some .Net code. On the face of it, that sounds similar to this case, which turned out to be due to EDMX, but in ...
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1answer
1k views

Can you have a WHERE clause with a greater than operator on a composite key?

I'm a web developer (not DB admin!) having performance problems processing a 1.7m record table on MySQL. Here is that table : CREATE TABLE `bbcmapimp_pc_raw` ( `postcode` char(8) NOT NULL, ...
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2answers
6k views

Mysql consumes a lot of memory

Here is my situation. I have an ubuntu server monitored by nagios. recently nagios sends alarms regarding the memory consumption on the server. I logged into the server and executed the top command ...
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1answer
134 views

Database performance for determining entities assigned to users

I am interested in insight in improving performance in the following instance: I am currently working on an application that has a hierarchical entity structure where, depending on a user’s level ...
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1answer
1k views

Replication slows down on massive deletes

First of all, I'm not a DBA, but I'd like to get advice how to deal with the following issue. We have few database servers based on SQL Server 2008 R2 SP1. They have been organized as shown below, so ...
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2answers
178 views

How can a key lookup with zero executions and zero actual rows take time?

I have a query that is taking about 10 seconds to run and I am trying to optimize it. All the time is spent in the key lookup which is fine however in this case if I mouse over the key lookup in the ...
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1answer
109 views

Are there significant performance differences when linking to a simple data view, rather than a data table, in a simple data view?

Sorry for the long question, but let me give you my scenario. I have a DB that houses data exported from another DB. The containing tables are copies from the other (non-SQL) database. Each column ...