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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9
votes
5answers
284 views

Getting a scan though I expect a seek

I need to optimize a SELECT statement but SQL Server always does an index scan instead of a seek. This is the query which, of course, is in a stored procedure: CREATE PROCEDURE dbo.something ...
1
vote
0answers
53 views

Query with join to a table on a different database need an index

I'm creating a query that one of its joins is made to a table from a different database. The query analyzer is suggesting the creation of an index, however I don't have permission to add objects to ...
0
votes
1answer
62 views

Oracle index usage

I came across V$SEGMENT_STATISTICS dynamic view. What statistic should I consider to tell if index block is being updated from time to time (on the contrary to scenario where index block is created ...
2
votes
3answers
87 views

MySQL query takes over a minute to complete

I am trying to pull calls associated with website visits from our huge database... I have got SQL that works, pulls correct results it just takes over minute to complete... Here is the SQL SELECT ...
2
votes
0answers
32 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, ...
1
vote
0answers
40 views

Mysql slow copying to tmp table to indexing

I try to indexing table. The table size is about 60GB. But indexing query is hang on 'copying to tmp table' 18 hours. I found advice setting 'myisam_sort_buffer_size' myisam_sort_buffer_size : 128M ...
3
votes
4answers
403 views

Is there any scenario where the existence of one or more Indexes in a table can prejudice it?

The title sums it up. I've learned and always heard that indexes in tables improve CRUD operations. A developer that I met last weekend told me that he does not like Indexes because they are bad - ...
0
votes
1answer
51 views

sqlite database table with 1000's of columns

I am using sqlite3 in an application to conduct an alalysis of distances between sets of points. Distances between these points have been precomputed using dijkstra's algorithim and left me with a ...
1
vote
1answer
78 views

Slow query performance on large table with no unique keys

I have a table that has approximately 20 million records and I'm having a very hard time improving the performance of the following query. It's taking well over a minute to run. SELECT ...
4
votes
2answers
141 views

Will the Query Optimizer Ignore A Fragmented Index?

Scenario: I have a heavy OLTP table with an index. I see many inserts, updates and deletes and the index fragments heavily within a day or less. While on day one of the index build, the optimizer ...
0
votes
1answer
31 views

Why is MySQL choosing that index?

I have a large indexed table with over 35 million rows. Here are the indexes, with a naming convention that shows their sequential column order: IDX_E93438363DAE128B, ...
0
votes
1answer
65 views

Innodb full table Scan

mytable is an InnoDB table with (a, b) as the primary key. Does this query check all table? Select * from mytable where ( b='2' and c='3') I want to find out if 'cluster' structure ...
0
votes
1answer
57 views

Creating index using dynamic SQL [closed]

I have following code for creating gist index CREATE INDEX web_stats_project_107_properties_crosspromo_gist_idx ON web_stats_project_107 USING gist (properties) WHERE properties @> ...
1
vote
0answers
53 views

PostgreSQL doesn't use index on inherited tables

I have two tables in PostgreSQL 9.4.5 deployed on Amazon RDS: an append only, weekly partitioned, All Positions table. These store all position readings from about 100,000 sensors. There are about ...
0
votes
1answer
47 views

MySQL optimizer difference between 5.6.27 and 5.5

We've just updated the MySQL version of the database of one of our clients from the 5.5 to the 5.6, everything is working fine except one simple query which is causing us troubles. Having the ...
0
votes
1answer
41 views

Will this SQL snippet REINDEX my GIN index? Why is it renaming an old index onto another?

I have a large PostgreSQL 9.3 database. One index on one table is quite large and appears to be bloated. I am using pgcompact from pgtoolkit to reduce database bloat without heavy table locks. However ...
3
votes
2answers
70 views

Should I normalise this database?

I have two database designs thought of for storing messages(instant messages) between users. It will be a group chat system. I have two table designs in mind. One is this: CREATE TABLE ...
2
votes
1answer
59 views

PostGIS - indexing - speed up query

I have this query (called from PHP, hence the $ variables): SELECT a.name, St_AsText(a.geom), b.name AS name_b, b.id FROM a LEFT JOIN b ON b.id = a.b_id WHERE ...
0
votes
1answer
51 views

Do mongodb's 2dsphere index works on multidimensional coordinantes array?

if i create a index like that : db.createCollection("users") db.users.ensureIndex({coordinates:"2dsphere"}); and then insert a point var point = { type: "point", coordinates: [ 1, 2, 3, 4 ] ...
0
votes
0answers
150 views

Database Design for group chat

I am creating a chat system as a RESTful API. This is what my design looks so far A request can be made to fetch the newest 50 messages that are part of a group id. Even if I do get a list of ...
3
votes
1answer
83 views

Aggregation GROUP BY bottleneck

I have a performance bottleneck with a SELECT GROUP BY operation. Schema I have a table like this: CREATE TABLE [InverterData]( [InverterID] [bigint] NOT NULL, [TimeStamp] [datetime] NOT ...
1
vote
1answer
72 views

Would adding an INDEX on varchar column in Mysql increase performance?

I have the following table to store log messages: CREATE TABLE `log` ( `id` bigint(20) NOT NULL AUTO_INCREMENT, `timestamp` varchar(40) COLLATE utf8_unicode_ci DEFAULT NULL, `logger` varchar(255) ...
4
votes
1answer
402 views

Why did adding a secondary index not increase select performance?

I have a table in MySQL called messages, which looks like this : id (primary key) | description | created_at(timestamp) This table is supposed to hold chat messages between users of my ...
6
votes
1answer
144 views

Index not used with `=any()` but used with `in`

Table t has two indexes: create table t (a int, b int); create type int_pair as (a int, b int); create index t_row_idx on t (((a,b)::int_pair)); create index t_a_b_idx on t (a,b); insert into t ...
3
votes
1answer
66 views

Does the principle of having an “ever increasing index” also apply for NVARCHAR and VARCHAR?

This might sound like an amateur question, but I just need to be 100% sure and I haven't found anything on it online. It is considered good practice having an "ever increasing index". Now, does that ...
3
votes
0answers
106 views

What's the point of prefixing each element in the column by its column number in multicolumn GiN indexes?

According to these slides which, I believe, are incorporated into the current implementation, each column element in multicolumn GiN indexes is prefixed by its column number and is stored separately ...
6
votes
2answers
529 views

Effect of an index on update statements where update column is not in an index

I constantly see people say that indexes slow down update, delete and insert. This is used as a blanket statement, as if it is an absolute. While tuning my database to improve performance, I keep ...
6
votes
1answer
362 views

What happens when we add an index to an existing table with a large amount of data?

I've a table which will contain around ~15 Million records. Now I need to add an index to the table. Adding an index will take some time to update every entry in the table. I'm quite confused ...
1
vote
1answer
64 views

Store Mysql Index in separate .Ibd file?

Is there any option to store table index in separate .ibd file? something like file_per_table mode? Becuase my table is growing more than 200gb. Table .ibd file have index for that table also. so If ...
-1
votes
1answer
57 views

Verify this TSQL to find the indexes fragmented over 50%

select OBJECT_SCHEMA_NAME(IPS.object_id) 'schema', OBJECT_NAME(IPS.object_id) as table_name,index_type_desc, round(avg_fragmentation_in_percent,2) 'avg_fragmentation_in_percent', si.name ...
4
votes
1answer
118 views

Index not being used in SELECT query

I have a table of about 3.25M rows with the follow format in Postgres 9.4.1 CREATE TABLE stats ( id serial NOT NULL, type character varying(255) NOT NULL, "references" jsonb NOT NULL, ...
3
votes
1answer
163 views

Do WHERE IN queries reindex the table after each set within the query?

I have a basic WHERE IN query that takes too long (30+ secs) to process. DELETE FROM `table1` WHERE ( djID, localID ) IN (("128","26"),("110","32")) The table I'm querying on has about 20 million ...
4
votes
2answers
103 views

Optimize a query with small LIMIT, predicate on one column and order by another

I'm using Postgres 9.3.4 and I have 4 queries that have very similar inputs but have vastly different response times: Query #1 EXPLAIN ANALYZE SELECT posts.* FROM posts WHERE posts.source_id IN ...
13
votes
4answers
1k views

Why would SQL Server ignore an index?

I have a table, CustPassMaster with 16 columns in it, one of which is CustNum varchar(8), and I created an index IX_dbo_CustPassMaster_CustNum. When I run my SELECT statement: SELECT * FROM ...
8
votes
2answers
217 views

Are columns which are not indexes, sorted on disk together with index?

Are columns which are not indexes, sorted on disk together with index, in MySQL, in MyISAM and InnoDB? An incorrect thought that I started to write: I think that probably not, since they are not ...
5
votes
2answers
114 views

Rebuild index in SQL Server does not reduce fragmentation

I am trying to reduce the fragmentation of my indexes. First of all I rebuild all indexes with fragmentation higher than 30%, but the most of my indexes still with high fragmentation or does not ...
4
votes
1answer
51 views

Index not being used for logical operation

We have a MySQL table with a few million rows. We have set of users identified by a flag which int value. We are facing a problem that mysql is not using index. For example, following query is very ...
3
votes
1answer
44 views

Fastest way to find (rare) rows with a null value among millions of rows?

If I have an addresses table with ~ 4 million rows in a Postgres database. Is there a way to optimize the following query so that I can find the few rows where address_id is NULL? Sometimes I need to ...
1
vote
1answer
93 views

SELECT Causes Performance Issue [closed]

I have a SQL SELECT statement that has joins on 27 of our warehouse tables. Original statement was taking more than an hour everyday so I decided to optimize it. I created some indexes but still it ...
3
votes
3answers
118 views

Manually create index fragmentation

Does anybody have a good approach to manually create a specific fragmentation to an index, ideally without increasing the number of rows in the underlying table? I need this for the purpose of a ...
3
votes
1answer
49 views

MySQL: Add column to unique index or add new index?

For a MySQL database, I have an InnoDB table name user_metrics with the following columns: id INT(11) NOT NULL AUTO_INCREMENT, userid INT(11) NOT NULL, name VARCHAR(32) NOT NULL, value ...
7
votes
1answer
136 views

Improving a DbGeography query

I am still new to database administration and I'm trying to optimise a search query. I had a query which looked like this and took 5-15 seconds to execute in some cases, and also was causing 100% CPU ...
4
votes
2answers
73 views

Indexed but still slow during query

I have a table that stores REST requests and responses: CREATE TABLE ws_call_logs ( id BIGINT NOT NULL, ws_method_id BIGINT NOT NULL, device_id ...
1
vote
0answers
23 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 ...
4
votes
1answer
166 views

Do indexes get transferred with pg_restore

I see other questions that have been answered in the negative (i.e. indexes do not get transferred over with the standard pg_restore). However, it looks like it did in my recent dump/restore and I am ...
0
votes
0answers
30 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" ...
3
votes
1answer
54 views

Index not being used in PostgreSQL

I have three tables, call them table1, table2 and table3. table1 has a foreign key column referencing table2, and table2 has a column referencing table3. Both foreign key columns have a B-tree index ...
3
votes
1answer
43 views

B Tree and B+Tree differences

I'm studying B+ Tree and B Tree and I would like to understand two things about it, if someone can clarify it to me I would appreciate: Why can I store more search keys on an B+ Tree Index? My guess ...
7
votes
1answer
123 views

Will a Full-Text Catalog with Track changes: AUTO automatically update if Change Tracking for that table is not enabled?

I have this database table that is suppose to keep the full-text index up-to-date. However I am not seeing it happening at all (no error in the log because the last log I see was when I triggered it ...
-1
votes
1answer
61 views

How to fix slow MySQL Joomla query(s)

I have a few slow mysql queries and i read that fixing it is easy by just adding indexes to the table. But as of what i am supposed to be indexing in these queries i do not know. (Or how) First query ...