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

learn more… | top users | synonyms

3
votes
2answers
141 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
1answer
14 views

Reusing covering index for fields in FROM, from another query's index

For the following query I have a covering index as so: SELECT bar_id FROM foo WHERE user_id=:user_id AND date_sent=:date_sent; ALTER TABLE foo ADD INDEX (user_id, date_sent, bar_id); Now I have ...
3
votes
0answers
45 views

PostgreSQL operator uses index but underlying function does not

I'm attempting to use JSONB with JDBC, which means that I have to avoid any of the operators which use the '?' character (as the PostgreSQL JDBC driver has no escaping for this character). Taking a ...
0
votes
1answer
17 views

How to know if 'mysql index' are used or not in all database or table?

I read similar topics without success :/ I'd like to know how can i determine which index are used in my database or table : DATABASE Is there any tools, or SQL to use on the database, which can give ...
0
votes
0answers
23 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 ...
2
votes
0answers
55 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
votes
1answer
117 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 ...
0
votes
1answer
17 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 ...
4
votes
1answer
156 views

How to optimize: having COUNT(*)>1

Without considering the indexes, Is there a way to re-write this query and get the same result quicker? select fo.OrderNo, fo.OrderItemSeqNo, COUNT(*) from Facts.FactBackOrder fo group by fo.OrderNo, ...
3
votes
2answers
81 views

When does SQL Server determine to use a new index?

I have been performing some maintenance on a server that runs some software the company bought, so I can't really change how the queries have been written. I have used some tools to determine some of ...
4
votes
1answer
122 views

Table with clustered Index consuming max memory causing low PLE alerts

For one of my server with below configuration i am continuously receiving alerts for low PLE which ranges between 20- 400 and an average of 90-100 in a day: Server: SQL server 2008R2 Databases : ...
0
votes
1answer
83 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 ...
2
votes
2answers
114 views

Uniquifier on Non-Unique Clustered Index vs Unique Clustered Index

Lets say for example that I have a table structured this way: ID1 int ID2 int ID3 int DTM datetime I'm only able to create a unique clustered index on the table if I include ID1, ID2, and ID3 (a ...
0
votes
1answer
43 views

mysql multiple column index Cardinality order

How does Multiple-Column Indexes work in MySQL? How is it stored internally? consider a table with Multiple-Column Indexes on two columns (X,Y). If X has High-cardinality than Y i.e., X is less ...
1
vote
1answer
24 views

Clear missing index DMVs

How can I clear missing index DMVs such as dm_db_missing_index_group_stats, dm_db_missing_index_groups and dm_db_missing_index_details? I don't have an option to restart the server or taking it ...
1
vote
1answer
28 views

How to determine efficacy of index on child side of foreign key

Given a parent-child relationship between two tables, such as: table ORDER order_id PK (already indexed) order_name table ITEM item_id PK (already indexed) order_id (FK to ...
0
votes
0answers
36 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 ...
1
vote
0answers
38 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 ...
1
vote
2answers
35 views

Optimal indexing for SELECT (mysql)

What indexes would you recommend for the following select (and why)? Keep in mind there can be tens of millions of rows. SELECT * FROM mytable WHERE md5 = ? AND created_at >= ? AND created_at ...
1
vote
2answers
378 views

Query Performance Tuning on a huge table

I have the following table Transactions. The table looks like this: CREATE TABLE [dbo].[Transactions]( [TransactionID] [bigint] IDENTITY(1,10) NOT NULL, [PlayerID] [bigint] NOT NULL, ...
3
votes
2answers
153 views

Using sp_BlitzIndex - Diagnosed as “Index Hoarder: Addicted to nulls”

Context: MS SQL Server 2012 In using Kendra Little's awesome tool, sp_BlitzIndex, a number of tables were diagnosed as "Index Hoarder: Addicted to nulls". I'm not looking for a debate over NULLs and ...
0
votes
1answer
17 views

Disable TTL thread in MongoDB

Is there any way to disable TTL deletion thread in mongoDB? I know that you can modify the ttl index expireAfterSeconds value to a high number in order to "technically" stop ttl from deleting, but i ...
0
votes
0answers
47 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 ...
1
vote
1answer
80 views

Rebuild index in table with many values

I'm junior DBA ,have table with 11 million values ,one of the indexes is like : CREATE NONCLUSTERED INDEX [ix_mytbl_mycolumn] ON [dbo].[myTbl] ( [my_id] DESC )WITH (PAD_INDEX = OFF, ...
3
votes
2answers
168 views

SQL Server 2008R2 XML Column Index strategy for large tables?

I am working with SQL Server 2008 R2 and some XML columns in a very large table. I understand that I cannot use Selective XML Indexes due to our SQL Server version being < 2012. I'm brand spanking ...
1
vote
1answer
69 views

Create nonclustered index on uniqueidentifier type

CREATE TABLE [dbo].[session] ( [id] [int] IDENTITY(1,1) NOT NULL, [user_id] [int] NOT NULL, [session_id] [uniqueidentifier] NOT NULL, [supervisor_id] [int] NULL, some columns .. ...
1
vote
2answers
2k 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 ...
3
votes
2answers
35 views

Do Postgres GIN indexes need to be rebuilt periodically?

Do they get bloated like btree indexes? If so how can the bloat be measured e.g. by an automated reindexing script. I am interested in improving query performance and saving space.
2
votes
1answer
553 views

Use GIN to index bit strings

I'm trying to extend PostgreSQL to index bit strings up to 1000 bits. (These bit strings are created by quantization of high-dimensional vectors, so for each dimension up to 4 bits are assigned). ...
1
vote
1answer
44 views

Taking the difference in timestamps between successive entries

This is my first foray into DBA.stackexchange, so I'll say up front: this is a query optimization question. If this is not an appropriate question for DBA, let me know and I'll skulk away quietly... ...
1
vote
2answers
124 views

Find out when your index was last rebuilt / reorganized

I've recently come across a database, which has very high fragmentation on large tables. Page count > 1'000'000 with fragmentation 99,... I would like to know how long this table has gone without a ...
1
vote
1answer
56 views

EXECUTE within function not using index?

I have an accounts table with ~200k rows and an index for these columns: account_type_id BIGINT , member_id BIGINT , external_id VARCHAR(64) CREATE INDEX account_full_qualifiers_idx ON ...
3
votes
2answers
99 views

Why postgres is using an odd index with no relation to the query

(Debian 7, Postgres 9.3, dedicated machine with huge cache) I have one big table called process_data (14gb) and another tiny lookup table called process_location. I'm doing a query between these two ...
0
votes
0answers
80 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 ...
0
votes
1answer
35 views

MySQL uses intersection instead compound index

I have compound index on following columns: (country_id, lazy, has_avatar, inactive, gender, id, age, challenge_count) When I run following query: SELECT COUNT(*) FROM `user_profile` WHERE ...
0
votes
3answers
80 views

Active/current (1-5%) and historical records in same table: index or partitioning?

I am trying to discover the correct architecture for the following situation. An application stores 'source data' in multiple tables. Each of these 'source data' tables contains actual, current, ...
1
vote
0answers
32 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 ...
1
vote
1answer
61 views

How to index a query `WHERE field IS NULL` (postgres)

So I basically have a table with lots of inserts, setting one of the fields (uploaded_at) to NULL. Then a periodic task selects all the tuples WHERE uploaded_at IS NULL, processes them and updates, ...
2
votes
1answer
86 views

Why am I getting cardinality issues when querying a single table

I have the following query: SELECT [iri].[RateItemKey], [iri].[RateItemType] FROM [prism72].[dbo].[ispRateItem] AS [iri] WHERE [iri].[Status] = 1 AND ( ...
2
votes
0answers
56 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 ...
0
votes
1answer
28 views

Join Operation using index defined?

I need to optimize some queries with several joins. I plan to create some indexes for these queries. I am currently using MariaDB with TokuDB storage engine. Should I expect the indexes for the join ...
1
vote
2answers
184 views

Should these two indexes suggested by the SSMS missing index feature be combined?

I'm trying to improve the performance of a specific query that is automatically generated by Entity Framework. I have run the query through SSMS, and it has suggested creating two missing indexes. ...
4
votes
1answer
324 views

How to setup complex multi-column index for massive table

I've searched what I could search on Google, SO, etc and haven't found an answer that would seem to fit what I'm looking for. I'm hesitant to make a post about this as I'm sure the answer is out there ...
1
vote
1answer
80 views

Reading a SQL Server Execution plan

I am very new to any type of tuning but have been learning more.. One of my specific databases one of the problems identified with slow queries are a number of Implicit conversions. It is my ...
2
votes
3answers
70 views

Change table scan in query plan to seek

I have an ORM generated query (Django) running against a local Postgres 9.1.11 instance that looks up ~5 records from two specific match fields. Due to the nature of the EDI load program, I need to ...
0
votes
0answers
25 views

DB2 LUW 9.5 ignoring indexes

I am seeing something in DB2 that I've never seen before. DB2_VERSION: 09.05.5 AIX VERSION: 7.1.0.0 I've got a query that is properly indexed. In fact, it’s heavily indexed. However, when I get the ...
1
vote
0answers
55 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 | ...
16
votes
2answers
6k views

Does a re-index update statistics?

I've been doing the MS10775A course this past week and one question that came up that the trainer couldn't answer reliably is: Does a re-index update the statistics? We found discussions online ...
2
votes
1answer
80 views

Adding Indexes To a Partitioned table in SQL Server 2012

I have recently converted our one large table to use table partitioning in SQL Server 2012. It's a table that stores logs based on a time. So I created a partition function to split the table on my ...
1
vote
1answer
324 views

Why isn't SQL Server using my non-clustered index and doing a clustered index scan?

Here are my full tables: CREATE TABLE [dbo].[tblCrawlUrls]( [cl_IdUrl] [int] IDENTITY(1,1) NOT NULL, [cl_CrawlNormalizedUrl] [nvarchar](200) NOT NULL, [cl_RooSiteId] [smallint] NOT ...