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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4
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1answer
1k views

SQL Server 2008 query planner failing after index drop & recreate

Recently we ran a script to our production DB that would dynamically drop and recreate hundreds of indexes as filtered indexes. While this script had run perfectly in all other previous tests, now ...
4
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1answer
212 views

Strictly only RAM matters?

I have to work on a project which would have a extra large table with billions of records but only two fields one is id and another is text. And id would be set to BIGINT and PK then if 8+2 (extra 2 ...
3
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2answers
209 views

Why seq-scan can be much faster than index-scan and index-only-scan in this simple query?

I am using PostgreSQL 9.4.4. I have a query like this: SELECT COUNT(*) FROM A,B WHERE A.a = B.b a and b are the Primary Keys of tables A and B, so there are B-indexes on a & b By default, ...
3
votes
1answer
539 views

Drop primary key without dropping an index

Is it possible to drop primary key constraint on a table without dropping the index? I have a situation when I want to remove the PRIMARY KEY to get rid of the NOT NULL constraints and set it to ...
3
votes
1answer
959 views

'ERROR: text search dictionary “unaccent” does not exist' during CREATE INDEX?

I'm running PostgreSQL 9.3 on Mac OS X Yosemite. I try to create an unaccent lowercase trigram index. To achieve it I did this: mydb=# CREATE EXTENSION pg_trgm SCHEMA public VERSION "1.1"; ...
3
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1answer
261 views

Very large btree index with few rows (openstreetmap gis data)

I tried to import a subset of open street map data to a Postgres database using the standard tool (osm2pgsql). I then tried to rebuild the indices on the table using plain sql (dropping them, then ...
3
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1answer
4k views

Very slow simple PostgreSQL query on RDS

I seem to be getting very slow queries on a medium sized RDS box (db.m3.medium, 3.7gb ram). This is across a table of 4,152,928 rows.. select sum(some_field) c from pages where pages.some_id=123 and ...
3
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1answer
871 views

Error when creating an index in SQL Server 2012

I'm trying to create the following index on our test environment (SQL Server 2012): CREATE NONCLUSTERED INDEX [iTransaction-OriginatingTransaction] ON [dbo].[Transaction] ( ...
3
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1answer
214 views

Minimum rowcount for filtered index?

Creating an index always has trade-offs. Whenever you insert, update or delete, it has to perform those operations on the index as well. This is all pretty commonly known. But with the advent of ...
2
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5answers
164 views

Lots of Indexes - MySQL vs MongoDB - Migrating

So, I've never used MongoDB, I just read a lot about it and I think it's going to be good for my project. Also, I do not have lots of experience with MySQL and to be even more honest I have no clue of ...
2
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1answer
126 views

what would be a good choice of clustered index (and other indexes) for this situation involving a indexed view?

To help me improve the performance of some queries I have created the following indexed view: CREATE VIEW DBO.vwOrders WITH SCHEMABINDING AS ...
2
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3answers
292 views

Why does PK constraint require a separate index when I already have a suitable unique clustered index?

This is part of table definition from here: CREATE TABLE [dbo].[JobItems] ( [ItemId] UNIQUEIDENTIFIER NOT NULL, -- lots of other columns CONSTRAINT [PrimaryKey_GUID_HERE] PRIMARY KEY ...
2
votes
1answer
306 views

Row with latest timestamp

How to get the row with the latest value in a TIMESTAMPZ column? Is an index needed? Does an index change the strategy? Would behavior vary by database (I'm using Postgres 9.4)? My app records data ...
2
votes
1answer
288 views

Index on column with data type citext not used

In PostgreSQL 9.4, with following schema: CREATE TABLE people ( id INTEGER PRIMARY KEY, name TEXT, junk CHAR(1000) ); INSERT INTO people(id, name) SELECT generate_series(1,100000), ...
2
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0answers
170 views

Finding missing_index_details in MySQL

MS SQL Server apparently can tell you what indexes would be useful for your query. Is there anything similar in MySQL? This article (scroll to "Find missing indexes") says that in Microsoft SQL ...
2
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2answers
87 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 ...
2
votes
2answers
236 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
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 ...
2
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2answers
221 views

Database events that will cause deletion of index

In SQL server if we try to change a data type of a column having index ,then it deletes the indexes associated with that column and changes the data type . I was not aware of it and was faced problem ...
2
votes
1answer
4k views

Query taking non-consistent time to execute [closed]

I have a query which takes large time to execute sometimes.When i checked the speed it was taking 15 seconds.But actually it should run faster than that.When i again checked the query it again ...
2
votes
4answers
2k views

When do I use another type index than integer? (eg string) [integer vs string index]

I was reading about relational databases like sqlite and I always see the schema for user storage like: UserID (index) | Username | Password but wouldn't it be actually much faster to use Username ...
2
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1answer
1k views

Does the size of the primary key contribute to table size?

I have a table (InnoDB) with data length around 36G and index length 23G. It had a composite primary key across three columns. As an initial attempt to reduce the size of this table, I dropped the ...
2
votes
1answer
82 views

Do I need to reenter old data after adding an index to a table?

I want to add index to my tables. Some of my tables already have couple thousand rows. Do I need to reenter my stored data after adding index to columns (to make them aware of index/so the indexing ...
2
votes
2answers
1k views

IN Clause causes Execution plan to change from Nested Loops to Hash Match

I'm tuning a query and have discovered some behaviour I'm not clear about. If I remove the WHERE IN clause the query runs in 3 seconds instead of 3 minutes. There only 7 rows returned in the ...
1
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0answers
31 views

What is the maximum value for the index_length of a MySQL 5.5 table?

I'm trying to find out why a series of inserts is painfully slow (1 minute 15 seconds, on average) on a dedicated MySQL 5.5.47 server, while the same inserts are normally fast (less than 5 seconds) on ...
1
vote
1answer
70 views

Multi-Column PK or Auto-Increment PK?

In another question I mentioned that I have a table where, in order to ensure uniqueness, I need to use multiple columns as the PK. However, lookups are usually only done using the first of those ...
1
vote
2answers
363 views

Estimation of creating index in SQL Server

We create new index on our production database, with a few fields, our database size is around 300GB and it works for one hour and do not finished yet. How can you estimate this operation? If we ...
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 ...
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
123 views

Is database record access sequential after retrieving the indexed page from disk? [closed]

This question was posted on Stack Overflow but left unanswered, I was hoping maybe here I might find an answer. What I understand about databases that if a queried or requested record is found in the ...
1
vote
0answers
183 views

Best practice for storing image order number in a database

I am designing a social networking website(mysql with InnoDB engine + php) where I need to store image sequence in a database. The table structure is as follows:- PicId (BIGINT, AUTO INCREMENT, PK) ...
1
vote
2answers
191 views

Should I create an index for non key columns?

I have a table in a PostGreSql database defined as following: CREATE TABLE public."MATCH"( "ITEM_A_ID" bigint DEFAULT 0, "ITEM_B_ID" bigint DEFAULT 0, "OWNER_A_ID" bigint DEFAULT 0, ...
1
vote
1answer
190 views

Optimizing Postgres query

I've got a one to one relation from users to addresses table. Where one user can have one search address and one verified address. I've got two indexes on addresses table : Index on state field ...
1
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0answers
872 views

Based on these DBCC SHOWCONTIG stats, should I index this table?

I have a SQL 2008 Standard server on full mirror (safety). I reorganize all indexes weekly. I am looking into rebuilding a few indexes to improve performance. I ran DBCC SHOWCONTIG on my largest, most ...
1
vote
1answer
91 views

Is an explicit KEY redundant if it is covered by a UNIQUE KEY?

I am auditing an application which I've been developing over the course of several weeks. I've noticed this in CREATE TABLE: UNIQUE KEY `baz_3` (`baz`,`foo`,`bar`), KEY `baz` (`baz`), Is the ...
1
vote
1answer
3k views

Varchar index - will hashing value make it faster?

I have a VARCHAR(1000) column in a table. It will contain strings that will not be guaranteed to be unique. I have a query that searches this column as part of a WHERE IN clause, the list of values in ...
1
vote
2answers
1k views

Mysql. Block/disconnect slow queries

I am experiencing issue. Someone 'attacked' my server: simply by searching the same phrase with multiple requests. As it is text search request and database indices are not used, the engine searches ...
1
vote
1answer
749 views

Change a partitioned global non-unique index that is the primary key to a non-partitioned unique index

One of the largest tables in our system has its primary key setup as a globally ranged partitioned (in huge, useless, multi-billion value ranges) non-unique index. Its values are just a sequence ...
1
vote
1answer
982 views

Slow insert with MySQL full-text index

I use a full-text index in a MySQL table, and each insert into this table takes about 3 seconds. It seems that MySQL rebuilds (a part) of the full text index after each insert/update. Is this right? ...
1
vote
1answer
399 views

Should indexes automatically be placed into their own bufferpool?

We work with DB2 LUW (specifically we are currently on 9.7 FP4) running on AIX. Per best practices from IBM, they recommend that when you build a table, you place the data, the indexes, and LOBs/LONG ...
0
votes
1answer
13 views

Postgresql error: failed to re-find parent key in index

I haven't seen this before and am stumped. I have a Django app with a postgresql 9.3 DB (hosted on Ubuntu VM), and very recently I VM ran out of disk space (resulting in no space left on device ...
0
votes
1answer
32 views

Necessary to have separate index for lookups against one of a multi-column PK?

Sorry if this is a FAQ, but I'm having problems turning up exactly what I'm asking: I have a table (mysql) with a primary key which is composed of multiple columns only because this is necessary to ...
0
votes
1answer
273 views

Increase performance WITHOUT adding indexes [closed]

I'm having a rather large table (350MB, 1.3M rows) and there are dozens of queries arriving at this table every second. Most queries are super-fast thanks to indexes - but some others aren't. ...
0
votes
1answer
373 views

Is ANALYZE useful immediately after creating an InnoDB index?

Let's create a new index on an existing table: CREATE INDEX `IDX_some_index` ON `some_table` (`a_column`, `another_column`); Is this useful? ANALYZE TABLE `some_table`; Can anyone point to ...
0
votes
1answer
68 views

query not taking index into account

EXPLAIN EXTENDED SELECT SQL_CALC_FOUND_ROWS SQL_NO_CACHE g.*, u.user_id FROM geotable g JOIN userstable u ON g.uid = u.uid -- corners selection: WHERE (lat BETWEEN ? and ? AND lon ...
0
votes
2answers
1k views

How to index for a query with independent range conditions?

What is the best way to index a table that I query using independent range conditions? E.g. WHERE X < ? and Y > ?
-1
votes
4answers
510 views

Index on 'GROUP BY' with functions

I have a log table. It logs visitor data (time of visit, browser, window size ...). I want to create reports. I use a query like this (MySQL): SELECT COUNT(*) as raw_views ... FROM logs WHERE ...