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

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82 views

Why does SQL Server use this index?

I have two indexes on a table with 786602 rows: CREATE NONCLUSTERED INDEX [IX1] ON [dbo].[O] ([A] ASC, [B] ASC) INCLUDE ([c1], [c2], [c3]) WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, ...
2
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1answer
60 views

Ways to Reduce Database Size and possibly improve performace. Untouched enviroment.

I am new to an environment. The Databases are virtually untouched by a seasoned DBA. I am looking for ways to reduce DB size and possibly improve performance. Unfortunately, I only have WEb edition ...
2
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1answer
711 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 ...
2
votes
1answer
502 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
82 views

How to speed up queries in MySQL on a table with ~50 million rows

The table has 4 columns of type datetime, smallint(6), tinyint(4) and decimal(15,5). The first 3 columns are PK. There are four indexes on the table: one with all the PK columns, and one with each ...
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127 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 variables/results from data analysis for quick selection in post-processing. If stored, I think it is well ...
3
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0answers
373 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 ...
2
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0answers
29 views

MySQL Performance issue: ~360ms to fetch 120 rows with 10 columns

I have the following tables: CREATE TABLE `events` ( `id` int(11) NOT NULL AUTO_INCREMENT, `status` varchar(255) COLLATE utf8_unicode_ci DEFAULT 'draft', `publish_at` datetime DEFAULT NULL, ...
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22 views

Combine several missing index suggestions with one index?

I investigate on missing indexes recommendations of my sql server engine. Looking at the most useful ones (for a specific table) that are candidates based on their potential usage and potential ...
2
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0answers
87 views

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 ...
2
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0answers
85 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 ...
2
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121 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 ...
2
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73 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 ...
2
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0answers
71 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]( ...
2
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0answers
91 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
766 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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42 views

Why does the first query scan and the second seek?

Please could somebody explain why the first query below scans on every JOIN to the REFERENCE_VALUES table but the second query seeks on the same JOINs. The first query does have other JOINs but I ...
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20 views

How to bucketize using Query optimal bucketization algorithm

I am trying to implement query optimal bucketization algorithm (QOB). The input of the algorithm is D=(V,F) where V is the value of the attribute and F is the frequency of occurrence. For EXAMPLE D ...
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28 views

Reasons why plans of sys.dm_exec_cached_plans do not match actual plans?

I re-assess index / query optimization and actually focus on key/bookmark lookpus that could be eliminated. Using a script of Jonathan Kehayas I go through the list of query plans that used those ...
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24 views

Index comparison

On my Production server (SQL2008) I have a query that returns suggestions of indexes. SELECT * FROM sys.dm_db_missing_index_groups g INNER JOIN sys.dm_db_missing_index_group_stats gs on ...
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27 views

DMV Index proposals still reported as missing

We have recently converted a big client running our patient/journal application from ORACLE to MSSQL, and after the conversion we have had quite a few performance issues. After running the DMV query: ...
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139 views

Script to find unused indexes over a period of time doesn't work in Oracle 11g

The statspack_unused_indexes.sql script described in this page would be incredibly useful to me, but it has been coded for an earlier version of Oracle. When I try to run it on 11g, I get the ...
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121 views

Slow Tally Tables

I have a pain point with a relatively large application concerning 'tally tables', which are used for keeping track of the number of items against 'campaigns' (placed by a client), and 'publishers' / ...
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108 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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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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24 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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203 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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221 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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196 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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101 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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71 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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113 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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55 views

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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1k 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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146 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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103 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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61 views

Index has no gain vs normal query

I have a table with a timestamp field. The table is loaded with rows which have ascending order of this field (time increases). I tried the following query, prior to establishing an index (there are ...
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23 views

Covered vs Noncovered Index & CRUD Sprocs question

I have what is a very simple question for most here I am sure. I would like to point out while i can run a query with the statistics on and get the answer, I would very much like an "under the hood" ...
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29 views

Minimum Oracle table size making IOT advisable?

I have inherited an IOT that doesn't seem to merit it because: only 25k rows fairly pure join table, non-index fields rarely queried total index width only ~125 bytes total row width only ~160 bytes ...
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66 views

MongoDB Slow updates

My application is doing extremely slow updates, despite my query being covered by indexes. My query is: query = {'spot': df_youtube['spot'].values[key], 'segment': ...
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0answers
179 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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0answers
38 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
70 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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20 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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0answers
48 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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86 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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77 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
73 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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47 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
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0answers
427 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?