2
votes
2answers
27 views

Mysql used key changes between two consecutive EXPLAINs

I have a huge unmaintained innodb table (~1.5billion rows), I just started to try to query it. I write && instead of AND once; and surprise! it uses different key! EXPLAIN EXTENDED SELECT * ...
1
vote
1answer
39 views

MySQL: does Index Merge Sort-Union access algorithm use temporary table?

My question is about index_merge optimization in MySQL. I have a query with a set of range conditions connected with OR. EXPLAIN of the query shows that index_merge method is used and the Extra ...
0
votes
0answers
26 views

What Index can I apply to a GROUP BY, MIN() and WHERE MySQL Query

I have the following table: CREATE TABLE `wp_prize_draws_log_copy` ( `id` int(11) unsigned NOT NULL AUTO_INCREMENT, `pid` int(11) NOT NULL, `entry_date` date NOT NULL, `entry_time` datetime ...
0
votes
1answer
50 views

Why is the index not used?

When I run the following querys in MySQL: SELECT count(*) FROM Inventory AS i WHERE i.lastModified > 1389920146804 or SELECT i._id FROM Inventory AS i WHERE i.lastModified > 1389920146804; ...
0
votes
1answer
41 views

Best Indexing Strategy for Query with Equality[A], Range[B], Group By[C], AND Order By[count(P)]

I have a poorly performing query: SELECT user_id, count(item_id) as count FROM table items WHERE category = 'magazine' AND created_at > 1384754400 GROUP BY user_id ORDER BY count(item_id) desc ...
0
votes
2answers
134 views

MYSQL - Why does this SELECT get slower the further down the table?

My table: CREATE TABLE `wp_users` ( `ID` bigint(20) unsigned NOT NULL AUTO_INCREMENT, `user_login` varchar(60) NOT NULL DEFAULT '', `user_pass` varchar(64) NOT NULL DEFAULT '', ...
4
votes
3answers
80 views

StackExchange clone: where should I add my indexes?

I'm creating an open source stack exchange clone and the following is my schema. What should I add indexes on for it to be optimal? Here is the schema in Rails format (SQL format below as well): ...
1
vote
2answers
111 views

Adding index to large mysql tables

I have a table | base_schedule_line_items | CREATE TABLE base_schedule_line_items ( id int(10) unsigned NOT NULL AUTO_INCREMENT, installment int(10) unsigned NOT NULL, on_date date ...
0
votes
0answers
39 views

is it good to add index on column used in group by clause?

I have a query like- select x, sum(y) from xyz where z>=100 group by x order by sum(y) desc; will it be faster if I am going to add index on x?
1
vote
3answers
149 views

Low Cardinality of Index performing better than High Cardinality?

For testing purposes I have 2 Tables TableA and TableB in an mysql-InnoDB, both with the same columns id bigint not null auto_increment, depot smallint not null, custno bigint not null, range_from ...
0
votes
1answer
125 views

How to optimize indexes on MySQL query with various sorts

I have an INNODB table levels: +--------------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | ...
1
vote
1answer
180 views

MySQL query optimization with aggregate ORDER BY

I have an analytics table that stores metrics aggregated the day level. I need to ask questions such as "For a given date range and client, what are the most popular items." The schema is as follows: ...
0
votes
1answer
118 views

Index for ORDER BY on aggregate in MySQL

I'm working with the following query: SELECT *, SUM(entries_count) AS entries_count FROM leads WHERE promo_id IN (1, 2, 3) GROUP BY user_id ORDER BY entries_count DESC LIMIT 25 OFFSET 100; It's ...
2
votes
2answers
113 views

Optimize query or model, to get an population overview in time

I think I've got a very simple model and query, but I cannot find a way to make use of indexes to boost performance. I wonder if there is a trick in my model, or MySQL query, to speed up the ...
0
votes
0answers
54 views

MySQL randomly refuses to use index

Mysql randomly refuses to use indexes for even simple queries. 1 example from slow-query log: # Time: 130904 12:19:59 # User@Host: cron[cron] @ [10.71.41.38] # Query_time: 58.488760 ...
1
vote
1answer
246 views

Would adding indexes to my foreign keys improve performance on this MySQL query?

Consider the following query: SELECT `locations`.`id` AS `location_id`, `locations`.`address`, `locations`.`lat`, `locations`.`lng`, `tickets`.`status_id`, `customers`.`name`, ...
0
votes
1answer
68 views

Indexes and Optimizations for Logging System

I'm designing tables for a new log system and am having trouble figuring out what indexes I'll need (I'm a developer, not a DBA), and am also open to any suggestions/criticisms/etc. for making the ...
0
votes
1answer
44 views

MYSQL - Using simple inventory number convention as Primary Key

I have an inventory with three numbered groups like so: Group 1: 0-999 Group 2: e0-e999 Group 3: v0-v999 Can I simply make a one-column table to store this information and make that column the ...
0
votes
1answer
89 views

Am I wrong in table design or wrong in selected index when made the table?

I've build web application as a tool to eliminate unnecessary data in peoples table, this application mainly to filter all data of peoples who valid to get an election rights. At first, it wasn't a ...
1
vote
0answers
80 views

Can't get rid of filesort on joined query sorting on second table

For some reason, this query: EXPLAIN SELECT * FROM biz as b INNER JOIN listings as l ON b.id = l.biz_id WHERE l.pub_id = 14 AND b.cat_id=310 ORDER BY l.level DESC, l.random DESC LIMIT 5; says it ...
0
votes
1answer
86 views

Two identical MySQL tables, one not using indexes

I have one MySQL Server (5.0.37) on a Linux Server that have many databases. Some of them (12) have each an identical table to log sensors data. Schema of one table CREATE TABLE `measuresHistory` ( ...
1
vote
1answer
652 views

Varchar index - will hashing value make it faster?

I have a VARCHAR(1000) column in a table. It will contain strings that will not be guaranteed to be unique. I have a query that searches this column as part of a WHERE IN clause, the list of values in ...
1
vote
1answer
45 views

Is it better to add an index and search via the index or add a unique constraint and let an insert fail?

I have a table with over 2.5 million records in production that keeps track of if a specific user has already viewed an job: mysql> DESCRIBE job_views; ...
1
vote
1answer
528 views

MySQL: logging queries which would execute without using indexes

I am trying to use log_queries_not_using_indexes = 1 to find queries which are not executing optimally on a MySQL server. However, I find the resulting log file of rather limited value. Apparently, ...
4
votes
1answer
706 views

What are the disadvantages if indexes are added on all columns?

I know, that it is not a good design to set too many indexes, but just for understanding the theory: What exactly are the disadvantages if you add an index on all columns in a table in MySQL? Are ...
2
votes
0answers
54 views

How can one improve the performance of a query that selects on a low cardinality column in MySQL?

I have a "State" column that has a low cardinality (three possible value), on which most of my queries perform an equality selection (WHERE col = 'blah') AFAIK you need something like a bitmap index ...
3
votes
1answer
78 views

What is a suitable index for this query?

Below query is taking long time - around 540 seconds. The table did not have any indexes. I created indexes on columns in the WHERE clause and other fields but the query is not using these indexes. ...
2
votes
1answer
994 views

Unique insert performance: Primary Key vs Unique Index

I have a table of unique values (domains_unique), with collumn domain varchar(255), with more than 20 mil records. What's the fastest way to insert into the table, by keeping the domain unique ...
1
vote
1answer
51 views

MySql include partition key in index?

Please look at the following Mysql table: http://pastebin.com/b0NDSbdz I've partitioned the table by sent_at and I'm making sure that most of the queries pass sent_at. do I need to include sent_at in ...
1
vote
1answer
106 views

Performance impact of including result column in indexed columns

I have a database (in MySQL, using InnoDB) that I am using for texture identification in a 3D image. In it, there will be a table of texels(texture pixels) with hue included, in the form of: texelid ...
1
vote
2answers
129 views

How to optimize this query?

Query: Select * from `t_event` where `create_user_id`=7 and (`event_create_date`)=('2012-12-18 00:00:00') and `event_type_cd`=11 and `domain_id` =602 and `job_id` =1 limit 1 Table structure: ...
2
votes
2answers
105 views

Optimizing index creation

One thing that has bothered me for awhile is creating many many indexes for the one table where the query only differs slightly or contains many of the same columns. An example case would be: table1 ...
1
vote
1answer
200 views

Simplify and optimize a complex query

Our site has a chronological event feed that uses MySQL. We have noticed that some of the queries tend to run for quite a bit longer than others. For example, some queries for our heaviest users take ...
1
vote
2answers
885 views

Best way to organize compound indexes on partitioned table (date by range)?

I have a table with an auto increment primary key, but in order to use the partition feature in MySQL I had to include the date in the primary key so I would use partition by range using the date ...
1
vote
1answer
151 views

What would be a optimal index for this query in mysql

I'm trying to optimize this query. SELECT * FROM sales_reps WHERE account_id = 1 AND (state = 'enabled') AND (clients >= 5 OR revenue >= 10000) ORDER BY name, platform, client_group, ...
5
votes
2answers
2k views

How can I improve the speed of a query on a 20 million+ row table?

I have a query that is used for getting internet traffic statistics of certain IP addresses. There are separate IP address fields for hosts and blocks of IPs called assignments. The data is stored ...
2
votes
1answer
101 views

Are two indexes needed?

Our MySQL database will contain an encyclopedia. The encyclopedia will be shown in pages where every page contains entries starting from a letter. Which indexes should I use? Should I have two ...
3
votes
2answers
99 views

MySQL using a index referencing a different column

I have a large table which uses a versioning system in the table. When a record is updated a new record is inserted with the old data and the original record is updated ( so to maintain the same ...
4
votes
2answers
371 views

Why is a secondary index chosen over a clustered index for SELECT COUNT(*) …?

In this query: select count(*) from largetable; a secondary index is chosen: mysql> explain select count(*) from largetable; ...
4
votes
3answers
196 views

Most efficient (or meaningful) way to index grid-based data

I have a MySQL table which I expect to be in surplus of a few million rows and 99% select statements. The problem I am having is coming up with a meaningful way to determine the Primary Key. (I have ...