The process of determining which indexes are useful and which are not.

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How to optimize indexes on MySQL query with various sorts

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

Minimizing Page Fetches

I have a complicated database structure and am trying to use it to retrieve Records based on multiple selection criteria from several tables. As a general rule, is it better to attempt to use ...
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1answer
45 views

Dropping old and creating a new clustered index

I am wondering what is the best approach for dropping and creating a new clustered index on a table within SQL Server 2008. My primary concern is the length of time it will take to perform this ...
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1answer
427 views

MySQL: Optimize query with a range and distinct count

I have a query on a large table with millions of rows that looks like this: SELECT COUNT( DISTINCT clicks.tx_id ) AS unique_clicks_count , clicks.offer_id FROM clicks WHERE ...
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1answer
425 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: ...
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1answer
91 views

Optimizing an Informix query — Specify architectural solutions if possible too (like caching service)

We have a huge query on an Informix database that is not performing well. The query is doing a join of 9 different tables. Maximum row count is just 40,000 rows. The query also has 9 sub-queries, and ...
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1answer
40 views

How to determine if an Index is uselss in Percona MySQL?

Using Percona Server 5.5 I've a table which stores user activty (lets call it user_activity). It was created quite a few years ago when I had only a little bit of knowledge about database ...
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1answer
48 views

How to order the where clause and join columns in a covering index?

Simple query example: Select t1.A, t1.B, t1.C, t1.CustomerID from table1 t1 join table2 t2 on t1.CustomerID = t2.Id where t1.A = 'x' and t1.B = 'xx' and t1.C = 'xxx' I created a non clustered with ...
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55 views

Indexes involved in intervals collision detection

Let's assume an hotel booking application wants to display all customers being present between two dates. Starting with a venue table : CREATE TABLE `venue` ( `id` INT NOT NULL AUTO_INCREMENT ...
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1answer
137 views

When to use hashtable over binary search tree vice verse for Database Index

Database Index can be constructed using binary search trees (BST) or HashTables , From my understanding so far , HashTables are superior to BST in terms of time taken for searching and insertions ...
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0answers
44 views

How to do Statistics in Partial Indexes of PostgreSQL efficiently?

This answer motivated think again my following tables but I am still uncertain how to store statistic data for quick selection. I think it is well done with partial indexes because only a subset of ...
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0answers
313 views

How to count selectivity rows in PostgreSQL 8.2

I have problem with two queries on PostgreSQL v8.2. It seem like the optimizer chooses a wrong index: db=# explain select count(*), messagetype, alias from event where templateinfoid = 10 and ...
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Unique Index much bigger than the table itself

Pg 9.3 on debian 7. I have a very huge table in rows, about 178 million (will turn 250 million in a week and then grow 500 thousand a day), but not that huge in size, wich is 20GB, it's a small ...
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0answers
60 views

Why would a default constraint be missing an index?

I have a query that looks at the sys.dm_db_missing_index_group_stats system view to determine what missing indexes there are for maintenance purposes. If I remove the filter from the query that ...
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0answers
97 views

Covering Index - Insert Performance

We are running some performance tuning on our database in SQL Server. The database in itself is pretty small with around 13 tables. But there are multi-level relationships between tables. When I try ...
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0answers
69 views

work/cache table issues, heavy inserts with heavy reads

we have a work table that stores availability of products. This table is updated with millions of inserts every night and medium amounts of inserts throughout the day. during the updates, we delete ...
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0answers
68 views

Can there be any case where it would require additional indexes while all columns compose primary key

Ok i don't know whether this question is asked before or not Here my table SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO CREATE TABLE [dbo].[tblProductPagesFeatures]( ...
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0answers
81 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 ...
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0answers
69 views

Query Performance - Why is a query slower when there are two criteria on the same column?

I have these two queries against a view, where I've added WHERE clauses against a date column (Indexed, Unique, Non-Clustered, Ascending): SELECT ColA FROM MyView a WHERE a.[Date] >= ...
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0answers
64 views

Multiple SQL Server Indexes, which ones to keep?

I am looking at my database that several people have worked on. A particular table is responding slowly when queried on a certain join. I notice some of the parameters of the join are not indexed. ...
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0answers
111 views

Rebuild/Re-organize index and Update statistics in SQL server

For many of the sql servers we have seen that the SQL agent Maintenance job first runs the re-indexing and later as a second step it update stats with full scan. I want to figure out if auto update ...
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0answers
99 views

Why is Update Query Slow with correct Indexes?

I have a query that updates a temp table. There are 2 Filtered indexes (by date) used in this query. However, the update take 8-10 mins to run. I am struggling to find out why it is so slow. There is ...
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0answers
69 views

MySQL not using multicolumn index on self join

I'm trying to optimise a query that performs an inner join with itself. The table size is currently 10GB ~50 million rows. /* Count all occurrences between start and end site id of a given speed ...
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0answers
63 views

I am not able to create/reindex a unique index in a table

I have a table that contains user locations (called public.user_location) and is the following: Column | Type | Modifiers id | ...
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83 views

Guidelines on best indexing strategy for varying searches on 20+ columns

I’m running a search engine for cars. It’s backed by a postgresql 9.3 installation. Now I’m unsure about the best approach/strategy on doing index optimization for the fronted search. The problem: ...
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Index Maintenance

I have a query thats performing badly and has a RID lookup. There are already quite a few indexes on the table and in the query stats I can see they are used although some less than others and all ...
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0answers
98 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 ...
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696 views

SQL Server Database Engine Tuning Advisor vs DMV queries

What is the best way to tune the indexes on my production database? I normally use the following query : SELECT user_seeks * avg_total_user_cost * (avg_user_impact * 0.01) AS [index_advantage], ...
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43 views

Is there some tricks to better index a URL column in postgres?

I'm working with a table that needs fast retrieve rows by its url column. But they all will be starting with http://www.: http://www.google.com http://www.amazon.com http://www.stackoverflow.com I ...
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32 views

PostgreSQL: raise error if planner needs to do an sequence scan

I want to check if our code does use only indexed columns. I think it does, but I want to be sure. How can I configure/modify PostgreSQL to raise an exception if it needs to do an sequence scan? It ...
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0answers
50 views

MySQL is pretty slow after 50-100k rows whats happen?

i have trying now a lots of time, and i try to find a way there make sense to find out of my problem, but this problem stil make a lot perfumes issues. i testing it of on a developer server ( 2 ...
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17 views

Index creation issue with MySql and Linux

MySQL Server database is installed on RHEL5.5 and db version is 5.6.20 Community Server. In MySQL database we have a table and it has 11,144 records. I am altering the table and adding index to it. ...
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19 views

MongoDB Sparse Index Query

I have around 40 million records in my collections but some million documents doesn't contain a field "catId". Sample Document : { "_id": ObjectId("5458b1a24669c5c0d66ae658"), "host": ...
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0answers
40 views

Why creating the missing index still shows it in the missing index dmv?

I followed the steps in this blog post to create the missing index and to clear it from the missing index dmv after running a select statement which uses the indicated column in the where clause and ...
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0answers
40 views

PostgreSQL indexing table on multiple columns

I have a table that holds half hour metering values in a compact form on a daily basis. The table has a structure as described below: day: timestamp without time zone, // describes a day ...
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0answers
149 views

Performance tuning self-joining MySQL query

I asked a question recently on the correct way to update a table using multiple joins to itself in order to generate the desired values. Updating MySQL innodb table based on multiple joins After ...
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0answers
46 views

Speed up sorting in this query

I'm trying to optimize the following plan and noticed that PostgreSQL spends a lot of time (relatively speaking) on sorting before the merge joins. Is there a way (using indexes, cluster the table, ...
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0answers
78 views

Index Tuning Question

I have the following query: SELECT T1.ITEMID, T1.ITEMTYPE, T1.PURCHMODEL, T1.HEIGHT, T1.WIDTH, T1.SALESMODEL, T1.COSTGROUPID, T1.REQGROUPID, T1.EPCMANAGER, ...
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59 views

Slow search times with functions despite index?

I'm aware that this question might be under the guidelines of being closed, but I'm out of ideas at the moment on how to optemize this table any further. Given a have a few billion records with ...
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0answers
63 views

MySql - multi-column index using only null values from one column

I have a Innodb table with a index that looks at 3 columns. ColA is integer and always has a value. ColB is varchar and always has a value. ColC is datetime and sometimes has a value (NULL). My ...
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0answers
38 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 ...
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176 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?
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980 views

Table Valued Function Very Slow

I have a TVF that when called takes 10 secs to run. However if I take the query inside that TVF, it takes only 1 sec. I have added correct indexes on this underlying query tables. In the Execution ...
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105 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 ...
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0answers
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Need Review - Index Rebuild and Index Reorganize strategy?

I've written a block of code to design Index Reorganize and Index Rebuild strategy based on following recommendation. I'm considering only Clustered and Non-clustered index, not Heap. Does anything ...