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.

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91 views

PostgreSQL isn't using indices in FULL OUTER JOIN

I have these tables I'd like to do a FULL OUTER JOIN between. They both have an index on (ts_minute, user_id, campaign_id, host_id) (which matches the join condition). In the following query, if I ...
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1answer
92 views

Multi table GROUP BY query optimisation

Currently I have a multi table/column GROUP BY query which is pretty slow. Below is the tables schema used by the query: report Table ...
2
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1answer
48 views

Performance of bitwise operators on byte column vs individual bit columns

I'm designing a database schema at the moment, but have a performance query. Our table needs to have (at least) two flags, or boolean values. We can call these IsComplete and IsExportable. The ...
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1answer
30 views

PostgreSQL : Where is index kept until check point occures ?

In PostgreSQL data is first written to WAL files. When commit is done, data is written to WAL files and then return to client (synchronous commit). When checkpoint reached or WAL buffer becomes full, ...
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1answer
439 views

No syntax for Nonclustered index in MySQL?

So, I have seen people discussing about differences between clustered V Non Clustered index, however, I didn't see any syntax for Non Clustered Index in MysQL. How does MySQL creates Nonclustered ...
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249 views

REORGANIZE seems to work as well as REBUILD all the time

On this MSDN Page it says if you should reorganize or rebuild based on the amount of fragmentation: 5% to 30% -> ALTER INDEX REORGANIZE Over 30% -> ALTER INDEX REBUILD WITH (ONLINE = ...
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0answers
56 views

Mongo find query is not using indexes in java code but working on mongo cosole

I found a strange issue. When i run mongo query from my java code with explain true it does not show me index used in the query but when i run it using mongo console it works fine . ...
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2answers
79 views

How can one optimize a query involving a sort and a LIKE?

Here is the query: EXPLAIN ANALYZE SELECT * FROM "Users" AS "User" WHERE "User"."name" LIKE 'garr%' AND "User"."id" NOT IN (2449214) AND "User"."hellbanned" IS NULL AND ...
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1answer
54 views

What is “cover-to-cover indexing”?

I came across this term reading my lecture notes; I can't find it on the internet. My notes say the following: Given a schema R(A,B) and a query of the form "A=a", or "B=b", or "(A=a AND B=b)". ...
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2answers
205 views

Optimizing a Postgres query with a large IN

This query gets a list of posts created by people you follow. You can follow an unlimited number of people, but most people follow < 1000 others. With this style of query, the obvious optimization ...
3
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1answer
241 views

Is a clustered index on a child table in a parent/child relationship the most optimal index?

A clustered index will sort row data in a table according to the ordering of the fields in the index. If so, why would you (or would you not) want to create a clustered index on the child table in a ...
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1answer
94 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 ...
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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 ...
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2answers
154 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 ...
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34 views

Very small indexes

What is the recommended best practice in dealing with indexes that store very little amount of data (like a few or few hundred pages)? Should these indexes be even maintained? Shouldn't they be ...
2
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2answers
149 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
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1answer
247 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
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1answer
291 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 ...
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2answers
741 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 ...
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1answer
36 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
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1answer
33 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
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1answer
294 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
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1answer
63 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'; ...
0
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2answers
122 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
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2answers
108 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
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1answer
106 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
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1answer
50 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] ...
6
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1answer
723 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
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1answer
190 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
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2answers
235 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 ...
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0answers
63 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
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0answers
48 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 ...
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2answers
71 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
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1answer
110 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 ...
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0answers
43 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
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1answer
133 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 ...
6
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2answers
427 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
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1answer
49 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 ...
0
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0answers
17 views

Missing index recommendation for an already existing index [duplicate]

SQL Server missing index DMVs suggest to create an index which already exists. The existing one and the suggested one exactly overlap each other; they are single (same) column index with no included ...
2
votes
1answer
133 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(' ', ...
1
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1answer
360 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?
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2answers
145 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 ...
5
votes
1answer
2k 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
126 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
881 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
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1answer
334 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 ...
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41 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 ...
0
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1answer
52 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
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2answers
518 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 ...
3
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2answers
85 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] ...