A database structure that can improve the speed of queries at the cost of disk space and slower inserts/updates. It stores a copy of one or more columns but structures the data differently to allow for faster access.

learn more… | top users | synonyms (2)

1
vote
1answer
306 views

Does the length of the index name have any performance impact?

This may seem silly, but in trying to stick to my standard nomenclature when naming indexes in our DB, the latest one was a little lengthy, and like all things DB I wondered if it in any way could ...
2
votes
0answers
43 views

Filtered Index is not selected once an identical, non-filtered, index is made [duplicate]

I have a lot of historical data, but 98% of the time, my data entry team only looks up data from the last 5 days. So I added a filtered index to help those lookups be faster. My test query looks ...
1
vote
2answers
408 views

Are nonclustered indexes used when joining tables?

I know that joins of type Sort-Merge don't use nonclustered indexes, because they work by sorting both tables and then joining them. But I've read recommendations to noncluster index all FKs, I ...
2
votes
2answers
237 views

Is unique index better than unique constraint when an index with an operator class is required

Postgres docs say: The use of indexes to enforce unique constraints could be considered an implementation detail that should not be accessed directly. One should, however, be aware that there's ...
2
votes
1answer
524 views

SQL Server : Index Seek with very high Scan Count [closed]

I have a query that joins 2 tables: Documents table, that has DocID as Unique Clustered Index DocumentsRows table, that has DocID, RowID as Unique Clustered Index When I join those 2 tables, I ...
6
votes
1answer
560 views

Timestamp-based index

I have a big database (200GB+) that contains some log info. And I want to speed up SELECT queries and stored procedures. I have a table with a GeneratedOnUtc datetime column, and have a non-clustered ...
2
votes
2answers
2k views

Updating large table (~6.5 million rows) & indexes

I'm trying to update a table with about 6.5 million rows in a reasonable amount of time, but I'm having some issues. We're adding a new column to an existing table and then setting a value for all ...
0
votes
1answer
41 views

Will a covering index save a table hit if only the commoly-used length of a `text` field is indexed?

I would like to add a covering index for a table that contains a text field. The maximum size of the field that is in use is ~2000 ASCII characters, 95% is below 800 characters. I am considering ...
0
votes
1answer
37 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 ...
4
votes
1answer
582 views

Unused index in range of dates query

I have a query that is not using existing indices and I do not understand why. The table: mustang=# \d+ bss.amplifier_saturation Table ...
1
vote
1answer
64 views

Is >58 hours to create an index normal? Should I cancel and try again?

I have an InnoDB table with ~43,964,557 rows containing 20.5 GiB of data (not counting existing indexes). mysql> show table status like 'backpack_items'; ...
3
votes
2answers
302 views

Will reindexing use the empty space or just grow table?

I have a table which is 170 GB and it has 98 GB of free/empty space. The free space was created by a massive deletion. If I run DBCC REINDEX or ALTER INDEX REBUILD, will the index use that free space ...
2
votes
2answers
216 views

How should I (re) index the table while keeping the transaction log small?

I have a 170 GB table in a database. It has 70% fragmentation on its index (index has multiple columns in it). The last time I tried DBCC REINDEX the transaction log blew up in the hundreds of GBs. ...
2
votes
1answer
145 views

Retrieving latest record using DISTINCT ON is slow [duplicate]

Using Postgres 9.4. I have a table cartests with 5.5M rows. Each row is a car test: \d log.cartests; Table "log.cartests" Column | Type | Modifiers ...
0
votes
1answer
99 views

SQL Server Table Index To big

I have a table that has approximately 450k records here is the structure of it CREATE TABLE [dbo].[Reviews]( [ReviewID] [int] IDENTITY(1,1) NOT NULL, [AuthorName] [nvarchar](50) NULL, [AuthorURL] ...
11
votes
1answer
1k views

Would index lookup be noticeably faster with char vs varchar when all values are 36 chars

I have a legacy schema (disclaimer!) that uses a hash-based generated id for the primary key for all tables (there are many). An example of such an id is: 922475bb-ad93-43ee-9487-d2671b886479 There ...
0
votes
1answer
345 views

MySQL performance of applying unique constraint single column vs combination column

I have a large MySQL InnoDB table containing around 137 million rows. I need to add a unique constraint to the table. We have two options: 1) A combination index on three columns, one of which will ...
0
votes
2answers
744 views

What indexes should one use to optimize a PostgreSQL query with a JOIN depth of 2?

Disclaimer: I am relatively new to PostgreSQL. I'm wondering how to optimize a query that does 2 INNER JOINs. My scenario is fairly simple: Select Posts with a photo (Posts.photo IS NOT NULL) and a ...
1
vote
0answers
69 views

Defragmentation of SQL Server 2008 indexes

I am having issues defragmenting indexes. I keep using the various defragmentation methods for defragmenting a SQL Server index such as DBCC INDEXDEFRAG and DBCC DBReIndex, but none seem to be ...
2
votes
0answers
63 views

ola hallengren Index Maintenance script - GUID Index

We been running ola hallengren Index Maintenance script and was ran into a problem with some indexes that have GUID as the Index Key, They are Frag and have a page count of 6,309, but they don’t get ...
1
vote
2answers
111 views

Creating index on large MySQL table taking forever

My table has 981 million rows and is about 30GB large. It is six columns: ID, Ticker, Date, Time, Price, Volume. The data was in text files and using LOAD DATA INFILE was actually quite painless and ...
0
votes
1answer
137 views

PostgreSQL SELECTs not returning correct result following recovery?

I took a copy of the current database from a live slave using pg_basebackup and recovered it to a brand new isolated computer following the instructions in the docs. Once the new database had started ...
0
votes
0answers
54 views

create_index_cost used_bytes vs alloc_bytes

I'm reading a lot about create_index_cost, but I can't seem to find out why there is such a discrepancy between the size of used_bytes and alloc_bytes. I know what each parameter means, but why is ...
0
votes
1answer
300 views

TokuDB + MariaDB 10: should I use a clustered index

I have a large table (200 Columns.. I know, but it wasn't my design) that will grow fast and I will have a lot of useless rows in it, identified by an IP (a varchar 32 column). The table will get ...
7
votes
2answers
1k views

Finding the query causing the missing index DMVs

How can I find the query causing the missing index DMVs suggesting to create a particular index? Thank you.
2
votes
1answer
62 views

Slow query on mid-size tables with good index coverage

I'm running a query that touches 2 moderately sized tables (1-5 million rows). EXPLAIN shows it touches only indexes and very few rows, however it takes very long to complete (~8 seconds). The only ...
3
votes
1answer
195 views

Should database be denormalized if I need an index across multiple tables

I have a catalog of album and song names. The song has a foreign key to the album table. I expect queries like: SELECT * FROM song s JOIN album a ON a.id = s.album_id WHERE LOWER(CONCAT_WS(' ', ...
2
votes
1answer
1k views

Dropping multiple KEYS of a table

Dropping multiple KEYS in a table is a preferred option or one by one is preferred? “DROP KEY A,DROP KEY B,DROP KEY C" For more 900 million records in the table. How does it work internally?
1
vote
2answers
242 views

Mysql might have too many indexes

I am using the php framework Laravel for my application, together with mysql 5.6, in order to have full-text search with innoBD. But I am not sure if I have too many indexes. My application allows ...
7
votes
1answer
5k views

Why not rebuild indexes with page count <1000?

I use Ola Hallengrens script for Index maintenance. Before I did that, I used the following query to see which indexes are fragmented most: SELECT dbschemas.[name] as 'Schema', dbtables.[name] as ...
1
vote
1answer
202 views

Is it worth indexing a varchar(32) column of UUIDS where half the UUIDS are v1 and half are v4?

I have a MySQL InnoDB table with tens of millions of rows. Each row has uuid column. They are stored in the standard VARBINARY(16). I was recently asked to add a column to this table of VARCHAR(32) ...
6
votes
2answers
1k views

Can rebuilding indexes cause worse performance after the rebuild is finished?

We have a customer database that is heavily fragmented - practically every table with more than 1000 pages has >95% fragmentation. Fill factors are set to sensible values, but page space usage is ...
1
vote
1answer
599 views

Index rebuild log growth

How much log index rebuild will generate.I remebered reading rebuild index should generate same amount of log file as table size.But my tests are showing otherwise.We need this estimate since we are ...
0
votes
1answer
87 views

Why Does the Update Statement also updates indexes?

I am currently learning about SQL queries and how indexes work with them, and I ran into a situation that I don't understand. Let's say I have this query for that updates a tables' values with another ...
3
votes
2answers
959 views

use an Index correctly to optimize queries

I have an SQL database with millions of records and when I'm querying the data like select * from ActCosts where ScenarioID= 456 The tables has 1,323,718 rows and it gives me like 50,000+ rows ...
5
votes
2answers
105 views

New Index on table cause table to be locked really often

Here are my tables : CREATE TABLE [dbo].[Trackers] ( [IdTracker] INT IDENTITY (1, 1) NOT NULL, [IMEI] NVARCHAR (16) NULL, [CreationDate] ...
2
votes
1answer
111 views

Indexed View - how to verify if it is worthy?

I have the following indexed view: CREATE view VProcessStatus WITH SCHEMABINDING AS select processstatus, StatusCount = COUNT_BIG(*) FROM DBO.tbltaxtransaction GROUP BY ...
2
votes
1answer
69 views

Dropped an index and recreated it in PostgreSQL 9.2, not used anymore

I have a table with 15M rows, with two indexes; one of them is a very simple BTREE on a string column. While trying to optimize some queries, I created a new partial index on the same column. Using ...
0
votes
1answer
682 views

Slow Postgres updates if OTHER columns are indexed?

Certain updates take far too long on large Postgres tables. Given these conditions: only one column is being updated, and it is non-indexed the column already has data in it for every row due to a ...
0
votes
0answers
127 views

Unique Constraint exception after dropping constraint

We had dropped a unique constraint using the ALTER TABLE DROP CONSTRAINT script, but it is still throwing the Unique Constraint exception while trying to insert. We drilled this down to two possible ...
1
vote
1answer
109 views

Index optimization on a view using a full outer join

Table structure: Foo FooChild Bar --- -------- --- ID ID ID Date FooID Date ...
1
vote
1answer
65 views

Which Indexes in which situations is more efficient in SQL Server 2012

I use SQL Server 2012. I want know when I want to know in what situation I have to use CREATE NONCLUSTERED COLUMNSTORE INDEX .... and in what situation I have to use Create NonClustered Index... ...
1
vote
1answer
405 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 ...
3
votes
2answers
1k views

space usage on sys.allocation_units and sp_spaceused

It is a known fact that the DMVs dont hold accurate information regarding number of pages and count of rows. However, when you have the stats updated, I can't see why they wouldn't. I am working on a ...
1
vote
1answer
181 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
494 views

Why wouldnt Mysql use index on the Primary query in a nested query

I have two tables: search_criteria and pricing. There is an index on search_id column in search_criteria table and on pricing_id column in pricing table. But running this nested query does not use ...
4
votes
2answers
1k 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
232 views

Full outer joins, coalescing, indexes and views

I have two tables, let's call them TableA and TableB. TableA TableB ------ ------ ID ID Date Date Foo Bar Both tables ...
3
votes
1answer
766 views

PostgreSQL 9.4 analysis, performance of normal column, indexed column and jsonb key

If I have a table containing: CREATE TABLE test( id SERIAL PRIMARY KEY, name VARCHAR(200), age INT, data JSONB ); and data column populated with {"name": xxx, "age": yyy}, sometimes ...
4
votes
2answers
261 views

SQL Server doesn't use expected index

I have the following query (simplified from an Entity Framework query, I don't have direct control of the SQL): SELECT TOP 15 HouseHoldingRuns.Id, ( SELECT TOP 1 ManCoId FROM ( SELECT TOP ...