MySQL : Open-Source, Relational Database Management System

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Is there a graceful or safe restart for mysql like for apache httpd?

I would like to restart mysql gracefully just like httpd where threads are served before restart. I would dislike queries breaking.
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MySQL transaction size - how big is too big?

I have an import process that runs every so often and I want it to be an 'all or nothing' kind of deal, aka: a transaction. There are many aspects, and the imports may yield anywhere between ...
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Mysql Innodb: InnoDB: ERROR: the age of the last checkpoint is InnoDB: which exceeds the log group capacity

I really need some mysql expertize. I am a newbi to mysql and I am seeing some server crash of my db in the past 1 week. I am using mysql 5.1.36 on Ubuntu. This is a dedicated mysql server with Dual ...
12
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1answer
9k 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 ...
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Database redesign opportunity: What table design to use for this sensor data collection?

Background I have a network of approximately 2000 sensors, each of which has about 100 data points that we collect on 10 minute intervals. These data points are typically int values, but some are ...
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1answer
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How to migrate large blob table from mysql to postgresql?

I'm now in process of migrating my MySQL database to PostgreSQL. Almost everything went fine (well, after lots of googling for correct mysqldump params etc.) except one table I have - actually the ...
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3answers
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Best way to design tournament database

I'm creating a webpage for placing bets on all matches of the upcoming Euro 2012 football tournament. Need some help deciding what approach to take for the knockout phase. I have created a mockup ...
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2answers
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Fastest way to change a 600GB table indexed key datatype from INT to BIGINT

I need to change a datatype from INT to BIGINT in a 600GB MySQL table. The column has a unique index. I might be good with unsigned INT, but I assume changing to that or BIGINT will be pretty much ...
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5answers
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Infrastructure for Highly Concurrent, High Write DB

My requirements are: 3000 Connections 70-85% Write vs Read Currently, we are maxing out a High-CPU, Extra Large Instance at 700 connections. All 8 cores are maxed. We think it's the number of ...
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2answers
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Is it safe to delete mysql-bin files?

I have MM Replication in mysql, and I want to squeeze some free space in the box be deleting unnecessary files, I came across these mysql-bin files inside /var/db/mysql/ There are hundreds of those ...
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5answers
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Where can I find the mysql slow log?

Just as the title says, where can I see it ? Are there any config options for it ( like how many ms would determine if a query is slow or not ) ?
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slow load speed of data from mysqldump

I've got a moderate size MySQL database with about 30 tables, some of which are 10 million records, some 100 million. The mysqldump of all the tables (into separate files) is fairly fast, takes maybe ...
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What is the default order of records for a SELECT statement in MySQL?

Suppose you have the following table and data: create table t(k int, v int,index k(k)) engine=memory; insert into t values(10, 1), (10, 2), (10, 3); When issuing select * from t where k = 10 with ...
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2answers
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How to select specific rows if a column exists or all rows if a column doesn't

I'm writing a script that gets a count of rows for a few tables, however for some tables I want to only get a count of rows where a flag is set (in this case active=1). Is there a way I can do this ...
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5answers
18k views

Why is DROP DATABASE taking so long? (MySQL)

New CentOS installation. I was running an import of a large DB (2GB sql file) and had a problem. The SSH client seemed to lose the connection and the import seemed to freeze. I used another window to ...
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3answers
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Why is 'LOAD DATA INFILE' faster than normal INSERT statements?

I've read an article that mentioned we can achieve 60,000 inserts per second by LOAD DATA IN FILE statement that read from csv files and insert it into database. Why should it differ from normal ...
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3answers
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Is innodb_file_per_table advisable?

We have an application where just one of the table will be growing into million of lines but the rest will just below a million. So what is the advice should we go with innodb_file_per_table or leave ...
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6answers
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Splitting Tables in MySQL. Good practice?

I have started working on an existing project and the previous developer had split up a table into 10 separate tables with identical schemas but different data. The tables look like this: ...
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2answers
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Does MySQL cache queries?

I'm interfacing a MySQL database with PHP Data Objects (PDO) and executing an extensive SQL query. Normally, it takes about 1500 ms; I still need to optimize it. When I run the PHP script twice ...
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4answers
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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 ...
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2answers
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innodb_file_format Barracuda

I have a couple questions for those more familiar. Most of my instances have been running Antelope despite having support for Barracuda. I was looking to play around with some compresses innodb ...
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2answers
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MySQL Sharding vs MySQL Cluster

Considering performance only, can a MySQL Cluster beat a custom data sharding MySQL solution? sharding = horizontal partitioning When I refer to sharding, I'm considering sharding made in the ...
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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 ...
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2answers
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How do I shrink the innodb file ibdata1 without dumping all databases?

InnoDB stores all tables in one big file ibdata1. After dropping a big table, the file is keeping its size no matter how big the table was. How can I shrink that file without having to dump and ...
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3answers
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Why am I getting `Impossible WHERE noticed after reading const tables` in explain query?

I have a unique compound key like fr(fromid,toid) in the table, when I run the query with explain I get the following result: Impossible WHERE noticed after reading const tables` The query I ran: ...
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2answers
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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 ...
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3answers
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MySQL instance stalling “doing SYNC index”

Problem An instance of MySQL 5.6.20 running (mostly just) a database with InnoDB tables is exhibiting occasional stalls for all update operations for the duration of 1-4 minutes with all INSERT, ...
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How to properly kill MySQL?

I have CentOS 64bit with CPanel installed and I use service mysql stop However, it keeps doing ..... for minutes and it never stops. It used to be instant. Any idea why it does that and how to fix? ...
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3answers
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MySQL table_cache and Opened_tables

I have seen people use the comparison of Open_tables and Opened_tables to assess whether the table_cache is too small in MySQL. However, I believe that Opened_tables is cumulative across uptime, so ...
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2answers
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Must an index cover all selected columns for it to be used for ORDER BY?

Over at SO, someone recently asked Why isn't ORDER BY using the index? The situation involved a simple InnoDB table in MySQL comprising three columns and 10k rows. One of the columns, an integer, ...
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3answers
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move data folder and drive mysql centos

i need to move the data to a different folder and drive on my cent os db server. i added new hard drive (since we ran low on space), i have a 1tb of hard drive and i have a new 2tb i want to put the ...
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3answers
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Where is the INNODB Performance Leak?

I have a weird problem which I cannot seem to fix. I'm more an web programmer than a Server/DB Admin, so I hope someone here can help me. The Situation I am working on a system which handles a lot ...
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1answer
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MySQL table with 100,000 records queried often

I have a single database of about 100 tables to store various kinds of information. The most important table is our order table which is used to store customers orders and is over 100000 records as ...
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3answers
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Use MySQL to regularly do multi-way joins on 100+ GB tables?

Background: I’ve created a web application that I would like to be able to scale reasonably well. I know I'm not Google or Twitter, but my app uses a fairly large amount of data for each user and thus ...
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1answer
185 views

MySQL Commited data not seen to select query

Context: The framework used is Spring and all queries are run with JdbcTemplate. Mysql Server version is 5.6.19. The table is an InnoDB table and defaults like auto commit and isolation level ...
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4answers
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Benefits of using backtick (`) in MySQL queries?

In MySQL we can create queries with or without the backtick (`) symbol. Example: SELECT * FROM TEST; SELECT * FROM `TEST`; Both works fine in mysql-console. Is there any technical difference ...
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3answers
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Why do we use Group by 1 and Group by 1,2,3 in SQL query?

In SQL queries, we do use Group by clause to apply aggregate functions. But what is the purpose behind using numeric value instead of column name with Group by clause? For example: Group by 1.
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1answer
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How is INFORMATION_SCHEMA implemented in MySQL?

The INFORMATION_SCHEMA is, in theory, a set of views specified in the SQL standard that allow the user to inspect the system's metadata. How is it this implemented in MySQL? When I connect to a fresh ...
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2answers
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MySQL Set UTC time as default timestamp

How do I set a timestamp column whose default value is the current UTC time? MySQL uses UTC_TIMESTAMP() function for UTC timestamp: mysql> SELECT UTC_TIMESTAMP(); +---------------------+ | ...
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2answers
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What is the safest way to switch the binlog format at runtime?

Because of the following warning in mysqld.log: [Warning] Unsafe statement written to the binary log using statement format since BINLOG_FORMAT = STATEMENT. The statement is unsafe because it ...
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3answers
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How to estimate/predict data size and index size of a table in MySQL

I am finding what is the best way to estimate size of a table for that i have studied lot of blogs and forums but unable to find any accurate answer For an example we have a table City with InnoDB ...
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Is it unwise to run replication on same physical server?

I'm contemplating setting up a Master-Slave replication for my database. The slave server will be used for redundancy and possibly a reports server. However, one of the biggest issues I'm running into ...
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3answers
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Where can I find example databases for MySQL, SQL Server and Oracle?

I want to experiment with the 3 large database management systems. For this purpose it would be cool to have the same database (the same tables, etc.) for each of those. Where can I find sql scripts ...
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4answers
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eCommerce orders table. Save prices, or use an audit/history table?

Im designing my first eCommerce schema. I've been reading around the subject for a little while, and am a bit confused about the relationship between an order_line_item and a product A product can ...
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3answers
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MySQL data type for 128 bit integers

I need to store 128 bits unsigned integers into MySQL and I was wondering what is the best data type to store such big numbers. Right now, I'm using binary(16) but that involves a lot of conversion ...
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3answers
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MySQL: how to restore table stored in a .frm and a .ibd file?

I have previously saved a copy of /var/lib/mysql/ddms directory ("ddms" is the schema name). Now I installed a new MySQL on a freshly installed Ubuntu 10.04.3 LTS by running apt-get install ...
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6answers
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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 ...
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2answers
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kill all queries - MySQL

Sometimes during a SNAFU I have to run kill query xxxxxxx twenty or thirty times. Any sort of kill all command I am missing? On account of how I don't like typing.
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Are there any MySQL Benchmarking tools? [closed]

I've heard a long time ago that there is this tool that helps you tweek mysql settings for better performance but i can't seam to find it. I am aware that I can use ab for apache to simulate high ...
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2answers
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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 ...