I'm new to MySQL and want to know that if I have a table with 25 column and the first one of it is the "id". Would the computer render every time through the whole table to search the particular "id".
if you construct the query like SELECT * FROM $table_name WHERE table_id=$id; then it will not render all table.
And as #dku.rajkumar says in the comment, it depends on what you want to fetch and your query structure.
It may depend on the query and also the STORAGE Engine you choose to use.
like MyIsam or InnoDb
example
CREATE TABLE tablename (
id INT UNSIGNED PRIMARY KEY
)ENGINE=MyIsam;
CREATE TABLE tablename (
id INT UNSIGNED PRIMARY KEY
)ENGINE=InnoDB;
there do exist difference in way tables are stored ,dependiing on storage engine , which certainly will reflect in the criteria mysql server (mysqld) performs search to cater your needs .
Related
A my-sql database table is having millions of data records.This table consists of a primary key [say user id],serial number [can have duplicates] and some other columns which allows null values.
Eg: say the schema is
CREATE TABLE IF NOT EXISTS SAMPLE_TABLE (
USER_ID INTEGER NOT NULL,
SERIAL_NO NOT NULL,
DESCRIPTION VARCHAR(100),
PRIMARY KEY (USER_ID)
)ENGINE INNODB;
Now I want to search a data row,based on the serial number.
I tried first adding a unique index including both columns [user id and serial no.] as
CREATE UNIQUE INDEX INDEX_USERS ON U=SAMPLE_TABLE (USER_ID,SERIAL_NO);
and then search for the data query based on serial number as below;
SELECT * FROM SAMPLE_TABLE WHERE SERIAL_NO=?
But it didn't success and I'm getting OOM error in mysql server side when I execute above select query. Appreciate any help on this.
You should not have added user_id intobthecindex you created. You just need an index on serial_no for that query.
If you provides necessary codes,it would be better than given explainations..However first you should find the id references to seraial number,then search the column corresponding to id
I have decided to use mysql sequence table, since I am using spring jdbc batch insert (can't get primary key with this feature), where I will be pass generated key while inserting each row, I have googled long time now, didnt get proper way of creating sequence table.
I have created a sequence table
create table table_sequence (value int not null) ENGINE = MYISAM;
but I feel it seems to be very basic, since I need to have max value, and cache limit for each instance.
I have many tables, do I need to have one sequence table for each table?
I have very less idea about db sequence, so suggestion are helpful to me. thanks
this may help you:
http://dev.mysql.com/doc/refman/5.0/en/example-auto-increment.html
CREATE TABLE animals (
id MEDIUMINT NOT NULL AUTO_INCREMENT,
name CHAR(30) NOT NULL,
PRIMARY KEY (id)
) ENGINE=MyISAM;
INSERT INTO animals (name) VALUES
('dog'),('cat'),('penguin'),
('lax'),('whale'),('ostrich');
SELECT * FROM animals;
I have a massive (3,000,000,000 rows) fact table in a datawarehouse star schema. The table is partitioned on the date key.
I would like to add an index on one of the foreign keys. This is to allow me to identify and remove childless rows in a large dimension table.
If I just issue a CREATE INDEX statement then it would take forever.
Do any SQL gurus have any fancy techniques for this problem?
(SQL 2008)
--Simplified example...
CREATE TABLE FactRisk
(
DateId int not null,
TradeId int not null,
Amount decimal not null
)
--I want to create this index, but the straightforward way will take forever...
CREATE NONCLUSTERED INDEX IX_FactRisk_TradeId on FactRisk (TradeId)
I have a plan...
Switch out all the daily partitions to tables
Index the now empty fact table
Index the individual partition
Switch all the partitions back in
Initial investigation implies that this will work. I will report back...
A short recap of what happened. I am working with 71 million records (not much compared to billions of records processed by others). On a different thread, someone suggested that the current setup of my cluster is not suitable for my need. My table structure is:
CREATE TABLE `IPAddresses` (
`id` int(11) unsigned NOT NULL auto_increment,
`ipaddress` bigint(20) unsigned default NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM;
And I added the 71 million records and then did a:
ALTER TABLE IPAddresses ADD INDEX(ipaddress);
It's been 14 hours and the operation is still not completed. Upon Googling, I found that there is a well-known approach for solving this problem - Partitioning. I understand that I need to partition my table now based on the ipaddress but can I do this without recreating the entire table? I mean, through an ALTER statement? If yes, there was one requirement saying that the column to be partitioned on should be a primary key. I will be using the id of this ipaddress in constructing a different table so ipaddress is not my primary key. How do I partition my table given this scenario?
Ok turns out that this problem was more than just a simple create a table, index it and forget problem :) Here's what I did just in case someone else faces the same problem (I have used an example of IP Address but it works for other data types too):
Problem: Your table has millions of entries and you need to add an index really fast
Usecase: Consider storing millions of IP addresses in a lookup table. Adding the IP addresses should not be a big problem but creating an index on them takes more than 14 hours.
Solution: Partition your table using MySQL's Partitioning strategy
Case #1: When the table you want is not yet created
CREATE TABLE IPADDRESSES(
id INT UNSIGNED NOT NULL AUTO_INCREMENT,
ipaddress BIGINT UNSIGNED,
PRIMARY KEY(id, ipaddress)
) ENGINE=MYISAM
PARTITION BY HASH(ipaddress)
PARTITIONS 20;
Case #2: When the table you want is already created.
There seems to be a way to use ALTER TABLE to do this but I have not yet figured out a proper solution for this. Instead, there is a slightly inefficient solution:
CREATE TABLE IPADDRESSES_TEMP(
id INT UNSIGNED NOT NULL AUTO_INCREMENT,
ipaddress BIGINT UNSIGNED,
PRIMARY KEY(id)
) ENGINE=MYISAM;
Insert your IP addresses into this table. And then create the actual table with partitions:
CREATE TABLE IPADDRESSES(
id INT UNSIGNED NOT NULL AUTO_INCREMENT,
ipaddress BIGINT UNSIGNED,
PRIMARY KEY(id, ipaddress)
) ENGINE=MYISAM
PARTITION BY HASH(ipaddress)
PARTITIONS 20;
And then finally
INSERT INTO IPADDRESSES(ipaddress) SELECT ipaddress FROM IPADDRESSES_TEMP;
DROP TABLE IPADDRESSES_TEMP;
ALTER TABLE IPADDRESSES ADD INDEX(ipaddress)
And there you go... indexing on the new table took me about 2 hours on a 3.2GHz machine with 1GB RAM :) Hope this helps.
Creating indexes with MySQL is slow, but not that slow. With 71 million records, it should take a couple minutes, not 14 hours. Possible problems are :
you have not configured sort buffer sizes and other configuration options
look here : http://dev.mysql.com/doc/refman/5.5/en/server-system-variables.html#sysvar_myisam_sort_buffer_size
If you try to generate a 1GB index with a 8MB sort buffer it's going to take lots of passes. But if the buffer is larger than your CPU cache it will get slower. So you have to test and see what works best.
someone has a lock on the table
your IO system sucks
your server is swapping
etc
as usual check iostat, vmstat, logs, etc. Issue a LOCK TABLE on your table to check if someone has a lock on it.
FYI on my 64-bit desktop creating an index on 10M random BIGINTs takes 17s...
I had the problem where I wanted to speed up my query by adding an index. The table only had about 300.000 records but it also took way too long. When I checked the mysql server processes, it turned out that the query I was trying to optimize was still running in the background. 4 times! After I killed those queries, indexing was done in a jiffy. Perhaps the same problem applies to your situation.
You are using MyISAM which is being deprecated soon. An alternative would be InnoDB.
"InnoDB is a transaction-safe (ACID compliant) storage engine for MySQL that has commit, rollback, and crash-recovery capabilities to protect user data. InnoDB row-level locking (without escalation to coarser granularity locks) and Oracle-style consistent nonlocking reads increase multi-user concurrency and performance. InnoDB stores user data in clustered indexes to reduce I/O for common queries based on primary keys. To maintain data integrity, InnoDB also supports FOREIGN KEY referential-integrity constraints. You can freely mix InnoDB tables with tables from other MySQL storage engines, even within the same statement."\
http://dev.mysql.com/doc/refman/5.0/en/innodb.html
According to:
http://dev.mysql.com/tech-resources/articles/storage-engine/part_1.html
, you should be able to switch between different engine by utilizing a simple alter command which allows you some flexibility. It also states that each table in your DB can be configured independently.
In your table . you have already inserted 71 billion records. now if you want to create partitions on the primary key column of your table, you can use alter table option. An example is given for your reference.
CREATE TABLE t1 (
id INT,
year_col INT
);
ALTER TABLE t1
PARTITION BY HASH(id)
PARTITIONS 8;
I am sorry if this is a dumb question (cause it sounds unlikely).
I have a table that is 20 Million rows. However, only about 300K of these rows get accessed regularly, and they can be identified in a column condition called "app_user=1"
Is there anyway i can just index those rows, and when I call a select, i will be sure to pass in the condition as well?
I would recommend splitting the table into two separate tables. But in case you don't want to do that, the highest performance way to do this if you're always going to include "where app_user=1" in your queries is to create a primary key on the table that includes the app_user column as the first part of the key. InnoDB will use this as a clustered index which saves you a few extra disk accesses. You can create the table like this:
create table testTable (
app_user tinyint UNSIGNED default 0,
id int UNSIGNED NOT NULL,
name varchar(255) default '',
PRIMARY KEY k1(app_user, id)
) ENGINE=InnoDB;
A friend wrote this article on clustered indexes in InnoDB a while back:
http://www.joehruska.com/?p=6
Add a column called app_user and index on that, then pass in "WHERE app_user = 1" in your query.
You could go further to partition your table based on that column.