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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Insert (write) performance

We are trying to speed up the queries in our application and in the process identified all queries which took more than 100ms. We noticed that there were few insert statements which took more than ...
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40 views

Why is logging “slow”?

On an empty transient table, inserting a single row took 50ms before changing it to UNLOGGED, 1ms afterwards. Why is this exactly? If the table structure is necessary, I'll post it, but it's only ...
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99 views

MySQL: How to avoid case sensitivity in SQL queries when migrate from Windows to Linux?

I have migrated my Database from Windows to Linux server. In many places, query has been written without focusing their cases (uppercase / lowercase). So, these queries are not getting executed and ...
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364 views

Does SQL Server allow INSERTs into tables and indexes to be written in parallel?

If I have a table that has many indexes, and I run a statement that inserts rows into the table, will SQL Server insert rows one-at-a-time, or will the rows be inserted using parallelism?
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37 views

Is it OK to duplicate parent field in child table for performance?

I have a very complicated query which involve more than 10 tables. Some parent tables are loaded only to search on one field. I wonder if I can copy this field in the child table (this data is never ...
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30 views

Performance Metrics for TempDB [duplicate]

I've been tasked with gathering performance metrics on a few database servers that have one TempDB data file. It seems prevailing wisdom is to have one TempDB data file per core up to a certain ...
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87 views

How to speed up looped INSERT INTO statements?

I currently use the following statement, for 10,000 rows it takes about 150 seconds. I tried removing the index on the target table, but this didn't help. Running the loop without the INSERT INTO ...
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1answer
356 views

Is SQL*Net message from dblink > 30% a performance issue?

I have a Java web-application running under Glassfish. App accesses Oracle using JPA (eclipselink). Last 2 days I'm observing some perfomance issues: some messages about long running queries (10 to ...
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90 views

Do triggers affect DB performance

I have a database with 250 small and medium sized tables. These tables are related with both MyISAM and InnoDB storage engines. There are multiple triggers that have been created on different tables. ...
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82 views

Will adding more indexes speed up using RedGate SQL DATA compare?

We want to use RedGate's SQL Data Compare to migrate user data from one DB to a DB on a completely different provider. This will be a time-sensitive operation as we do not want our site offline for ...
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451 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
112 views

Optimizing a large number of INSERT … SELECT statements

I have a MySQL InnoDB database with two tables related by a foreign key. Each time a row is inserted into one it uses an INSERT ... SELECT statement from the other to get the corresponding foreign ...
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1answer
574 views

SQL Server PerfMon: Compilations/sec > Batch Requests/sec

I've been looking at various PerfMon metrics on one of our client's SQL Server instances trying to get a good gauge of where our database (or server) could use improvements. One measure that has me ...
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35 views

more queries vs storing results in database

Environment: Embedded (smartphones) Data Structures: Object Table A: id, field1, field2... Object Table B: id, field1, field2... Object Table C: id, field1, ... , Object A, Object B ... many ...
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1answer
67 views

What are possible causes for consistently volatile INSERT performance in MySQL tables?

I have a Java program running on a VM that is sequentially feeding a queue of single row INSERTs through a single connection to a MySQL server on the same VM. The queue execution is not artificially ...
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1answer
48 views

How to efficiently count rows in a query by limiting the number or found rows?

I have a website where I output a pagination with a limited number of pages, let's set it to 50 for example. That is, if there are actually 51 or more pages of content the 50th will be the latest that ...
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251 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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49 views

Is a single batch request equivalent to a single tsql request?

I'm looking into some performance metrics and every recommendation includes monitoring Batch Requests/sec. But, maybe a silly question, does a singe batch request correspond to exactly one tsql ...
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1answer
52 views

How to prepare executon plan for given sql query on a server with 4 processors (Oracle database)

4 processors means the query runs in parallel. Select /*+ parallel(4) */ T1.A FROM T1,T2,T3 WHERE T1.A = T2.A AND T1.B=T3.B AND T1.C=T3.C Tables T1,T2 and T3 have 4,8, and 16 partitions ...
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229 views

SQL server query is slow *without* including execution plan

I have just set up fresh installation of SQL Server 2012 on a new server and I'm experiencing very strange performance problems. Long story short, for some reason not including execution plan makes my ...
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3answers
329 views

best practice for 'staging' relation in stored procedure: use temp table, or view?

When I write stored procedures that take relation A and output relation Z, I like to create 'staging' relations along the way, so I can inspect the state of the data after each step in the programming ...
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1answer
113 views

PostgreSQL - Out of memory on count group by query

I'm trying to execute the following statement in PostgreSQL database: create table tmp_nodes as select node_id,count(way_id) as count from way_nodes group by node_id; This query fails because the ...
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59 views

Adding additional condition significantly degrades performance

Have the following query: SELECT * FROM table_A INNER JOIN table_B ON /* conditions */ INNER JOIN table_C ON /* conditions */ INNER JOIN table_D ON /* conditions */ WHERE table_B.state = 'active' ...
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96 views

SQL Server - Data and Log Separation

We have a SQL Server 2008 R2 which has, among others, a 12K RPM HDD and a 7.2K RPM HDD. The original intention was to store the data files on the 12K drive and the log files on the 7.2K drive, as is ...
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262 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 ...
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99 views

Need help tuning my.cnf file

I need help tuning mysql. Currently it is using a lot of CPU. I dont find any query that last longer than 3 seconds in SHOW PROCESSLIST and there are only around 20-25 running most of the time. Still ...
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2answers
87 views

Does having many databases affect MySQL performance?

I have huge unused databases in MySQL. Do they affect my MySQL engine performance even if they are unused? Do they consume memory on their own? Thanks
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181 views

Are mongodb bulk inserts really increase server perfomance (and faster)?

Bulk inserts always are faster in client side because of saving round-trips, but at the server-side is there any sensible performance improve? It seems the code for bulk inserts, just loops over ...
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134 views

Best design of mongo replica set for DB read/write speed

I'm building a Node app that uses MongoDB. Whilst it would probably be fine to have node and mongo sitting on the same VPS, I want to ensure that the MongoDB is backed up and maintain high ...
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2answers
66 views

Index is not used with same Query on two Servers [closed]

I have two notebooks with same specs (same model, only ram is 24GB/32GB, same ssd) and exact same database and same sql server version. SQLIO is 3300 and 3600. Now I run a query on one notebook and ...
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1answer
138 views

Optimistic Paging and separate query for COUNT?

I am using SQL SERVER 2012 FETCH/OFFSET after searching a lot that this will give me the best performance. But for paging to work, I need a Total count. There are 2 ways to achieve this. 1) Paging ...
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1answer
103 views

Optimizing a slow MySQL query

I'm trying to optimize a ~100GB database. All data values are in one single innodb table, is this bad? Here's what a common query looks like: SELECT `CensorCode`, `LocalDateTime`, `UTCOffset`, ...
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77 views

Any way to speed up my queries in MariaDB with tables less than a 4 GB in size?

I'm doing some text mining work and a bit frustrated that queries are taking 6 to 10 minutes to run. My workstation has a 3.5ghz Xeon, 32GB of RAM, and 2 SSD as RAID 0. Is it possible to do ...
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48 views

How can I rewrite the following removing the date_format function?

I have a table with a column when that is of type datetime. I am doing the following filter which can not use and index: AND DATE_FORMAT(t1.when, '%Y-%m-%d') <= LAST_DAY(now() - interval 1 month ) ...
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1answer
47 views

Impact of replication compression & encryption on performance, traffic?

What is the impact of MySQL compressed-slave-protocol on replication traffic? According to High performance MySQL it can lower the traffic to a third of the same replication without the compression. ...
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1answer
156 views

Increased performance from single statement, multiple row inserts?

I'm currently obsessing over bulk inserts via prepared statements with libpqxx. I am far from a database expert and even further when it comes to Postgres, but just thinking superficially, it doesn't ...
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27 views

Performance : MySQL replication or only one big server?

I'm searching about the best choice. We have to host a website with 10.000 - 20.000 visitors per day actually, growing. At the beginning, which would be the best : Having 2 MySQL servers (12 GB ...
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1answer
108 views

What mongodb database layout would fit better

I'm currently writing an application using the MEAN stack, pretty much only for fun and because MEAN is "cool" at the moment. Therefore I'm thinking about the database layout. The data needed to be ...
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2answers
291 views

How to fix slow LIMIT queries with big offsets without heavily rewriting them?

Imagine a very basic example of your average discussion board. For example: CREATE TABLE threads ( id INT UNSIGNED NOT NULL AUTO_INCREMENT, title VARCHAR(100), PRIMARY KEY (id) ) CREATE ...
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9 views

Improving the performance of this select query [duplicate]

i have two tables TABLE 1 and TABLE 2 And i am running this select query to fetch the data , it takes long time to run SELECT TABLE1.* , TABLE2.COL1 , TABLE2.COL4 FROM TABLE1, TABLE2 WHERE ...
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169 views

How to improve the performance of this select query?

I have two tables: TABLE1 and TABLE2. And I am running this select query to fetch the data. It takes long time to run: SELECT TABLE1.* , TABLE2.COL1 , TABLE2.COL4 FROM TABLE1, TABLE2 WHERE ...
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2answers
206 views

Oracle becomes too slow after system crash [closed]

I am using Oracle 11.2 as a database for my application. For this purpose I should import my data (around 100m records) to this database. For this purpose I used SQL Developer. Unfortunately at the ...
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51 views

Big Mysql table optimization

I have a table that I use to cache google translate API answers. Table structure is orig_string and group are indexes Now it has more that 1million rows with 35000 distinct values in group field. ...
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29 views

“dynamic set” in a MySQL table

I have a table where one column will have a few values many times (maybe 20 different values). Now I would like to use something like the set to improve performance and memory consumption. The problem ...
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1answer
117 views

Slow MySql server - even on a super fast server

I have just upgraded my 12 year old server to a really fast new one. It is a dedicated server, Dell R620 1 x Intel E5-2620 (2.0GHz, 6C) CPU 32GB RAM - 4 x 250GB SSD RAID 1, in short vastly faster in ...
6
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2answers
321 views

Improve performance of COUNT/GROUP-BY in large PostgresSQL table?

I am running PostgresSQL 9.2 and have a 12 column relation with about 6,700,000 rows. It contains nodes in a 3D space, each one referencing a user (who created it). To query which user has created how ...
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478 views

A little clarification on how 'LIMIT' works

Not being a full blooded member of the DBA clan, but more of a dev clan, I find myself trying to figure out some slow running queries. The subject of my question however is not 'Why my queries are ...
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63 views

Oracle result cache behaviour

Oracle by default caching the query results and function results(Buffer cache). I have noticed this with AutoTrace utility, where the physical reads are huge on first execution, but from next ...
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177 views

Inserting to table: Insert rows with Left Outer Join or Insert rows then Update?

I have a table of Orders and another table of Deliveries. The Orders table will contain a reference to the Deliveries table if there is a corresponding row. Not every row in Orders will have a row in ...
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141 views

HOW does ROWNUM work with this “optimization”

I'm trying to optimize a query in which I have some requirements where I need to be able to arbitrarily select a row ROWX from a query. Why is it that SELECT XML_DATA FROM (Select ROWNUM AS ...