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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3
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2answers
133 views

Clarification on Clustered index scan and Clustered Index Seek

I have created one table with 80000 records with Cluster Index on CustomerID column. When I queried the following statements the execution plan behaves in differently. Can anyone clarify the same. ...
1
vote
1answer
43 views

Using indexes in ORDER BY MySQL

Here i have table with indexes and more than 700000 entries. CREATE TABLE `t1` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT, `title` char(255) COLLATE utf8_unicode_ci NOT NULL, `cat_id` ...
1
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0answers
13 views

Add index to mysql table with ndbcluster engine

I'm having trouble while adding index on mysql table with ndbcluster storage engine below is the error . [mysqlcluster ver. 7.4 GA] mysql> alter table `sks_staff_office` add index `pid_index` ...
2
votes
1answer
33 views
+100

Increase in IO Wait after adding indexes with postgres

I've recently been put in charge of a system that has been fairly untended for a period of time. The majority of activity is via queued worker jobs based off of data feeds from other systems/data ...
1
vote
2answers
83 views

Index not used on partitioned table

We have a table similar to this one mysql> SHOW CREATE TABLE my_requests\G *************************** 1. row *************************** Table: my_requests Create Table: CREATE TABLE ...
1
vote
1answer
147 views

How to speed up queries in MySQL on a table with ~50 million rows

The table has 4 columns of type datetime, smallint(6), tinyint(4) and decimal(15,5). The first 3 columns are PK. There are four indexes on the table: one with all the PK columns, and one with each ...
0
votes
0answers
5 views

MongoDB ixscan seems to be scanning more objects than expected

I'm using MongoDB 2.6.12 and a collection has the following index {a: 1, d: -1}. In case the types matter a is a Number and d is a Timestamp. From what I can see in the code we are limiting this ...
3
votes
1answer
770 views

Do OR conditions in Oracle SQL queries spoil index use / cause full table scan?

I have a query on Oracle 11g of the following type, which results in a series of highly inefficient full table scans: select t.Id, t.ObjectId, t...[other Tasks columns] , od1...[ObjectData1 ...
1
vote
1answer
169 views

Using index on datetime field not working really

Here is my query select msisdn, sum(score) as score from contest_player_update_history_ideacontest6_35 where request_date >='2015-01-14 00:00:00' and request_date <= '2015-02-03 23:59:59' ...
0
votes
3answers
72 views

What is the performance impact of indexing a frequently updated column?

I just want to know if I'm doing this right. I've searched google for hours already and I can't find a straight answer. I have a table with potentially a very large amount of inserts and updates. Any ...
1
vote
1answer
17 views

MySQL 5.6 Online DDL lead to to much table-metadata-locks when I just add index

It's normal that table-metadata-lock shows up for a short time when ALTER TABLE t add index ... starts and ends. But I have encountered all DML operations blocked in Waiting for table metadata lock, ...
1
vote
2answers
364 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
30 views

Dynamic script to Drop Indices of a specific column

I´m currently writing an SQL script to update our database and for that I need a script to drop indices that rely on a specific column (because I also want to drop the column). In my script I have ...
8
votes
1answer
289 views

Is the WHERE-JOIN-ORDER-(SELECT) rule for index column order wrong?

I am trying to improve this (sub-) query being part of a larger query: select SUM(isnull(IP.Q, 0)) as Q, IP.OPID from IP inner join I on I.ID = IP.IID where ...
1
vote
1answer
18 views

Perfomance of CREATE INDEX vs CREATE INDEX CONCURRENTLY in PostgreSQL

I know CREATE INDEX CONCURRENTLY is slower, but how many longer it will takes to finish in comparison with the traditional CREATE INDEX? 40% more or much more than that? I am creating an index in a ...
1
vote
1answer
46 views

Oracle index with REGEXP_REPLACE is it a good idea?

I have a table of contacts with 1 million registers and now the user wants to search in it by the telephone. Trying to avoid a fullscan I decided to create a new index in this column, but the trick ...
10
votes
2answers
10k views

How to choose a collation for international database?

I'm designing a database which will store data in different languages (using UTF-8), so I think the best way to display the query's results is ordering it according to the user's language during the ...
1
vote
1answer
15 views

What run-time configuration parameters are used for concurrent index creation

Suppose I were to run the following. The first line shows the server's default maintenance_work_mem value. mhildreth=# show maintenance_work_mem; maintenance_work_mem ---------------------- 16MB (1 ...
0
votes
0answers
14 views

potgresql foreign key index unused for some columns on one specific server

I have a table publication, with two columns type_id and sub_type_id (there are, of course, more columns, but they are not important) on a server, all containing int8 foreign keys to tables type and ...
1
vote
1answer
60 views

Should I remove this clustered index?

I have lots of tables designed similar as the following (slightly simplified) sample. The original table on different servers has between 50,000 and 200,000 rows (around 12,000 - 150,000 pages). ...
11
votes
2answers
409 views

Minimizing Indexed Reads with Complex Criteria

I'm optimizing a Firebird 2.5 database of work tickets. They're stored in a table declared as such: CREATE TABLE TICKETS ( TICKET_ID id PRIMARY KEY, JOB_ID id, ACTION_ID id, STATUS str256 ...
5
votes
1answer
849 views

Should one always VACUUM ANALYZE before REINDEXing in PostgreSQL 8.4?

Early in the morning every day a pgAgent job refreshes the contents of table A from table B on my PostgreSQL 8.4 database. Table A contains around 140k records across 91 columns and has two indexes - ...
0
votes
0answers
31 views

Building MySQL InnoDB clustered indexes

Assuming that you have a table like CREATE TABLE `t1` ( `search_id` int(11) NOT NULL, `provider_id` bigint(20) unsigned NOT NULL, `status` text NOT NULL, `imported_at` int(11) NOT ...
2
votes
0answers
29 views

How is Index rebuild affected by IN_ROW_DATA vs LOB DATA

I am using Ola Hallengren's scripts to maintain my databases. On a few of them there are indices that don't seem to be benefiting from the maintenance. I know that his scripts have a lower threshold ...
5
votes
1answer
65 views

Index creation leads to large transaction log growth

I have an approximately 1 billion row table. I then create an index as follows: CREATE NONCLUSTERED INDEX [IX_Index1] ON [dbo].[MyTable]( [CustomerID] ASC ) -- CustomerID is uniqueidentifier WITH ...
1
vote
2answers
58 views

Trigram index for for ILIKE patterns not working as expected

I've got a simple but slow query: SELECT DISTINCT title FROM ja_jobs WHERE title ILIKE '%RYAN WER%' AND clientid = 31239 AND time_job > 1457826264 ORDER BY title LIMIT 10; Explain analyze: ...
14
votes
3answers
1k views

What is the optimal data type for an MD5 field?

We are designing a system that is known to be read-heavy (on the order of tens of thousands of reads per minute). There is a table names that serves as a sort of central registry. Each row has a ...
0
votes
1answer
20 views

Different behaviour between oracle and postgres regarding alter table primary key command

In Oracle 11g, when you write alter table abc add constraint abc_pk primary key (one, two, three); Automatically an index for one, two, three is added. In PostgreSQL 9.5, when you do the same, ...
0
votes
1answer
136 views

Does remove document automatically remove the index that reference this document?

I am wondering if removing the document will automatically update the index if this document is referenced?
-3
votes
1answer
30 views

Database engine disk access [closed]

Do you know what is the difference between the database engine get rows in a table without and with use of an index in a disk prespective. They way the engine access the table in disk is the same when ...
1
vote
1answer
179 views

Index to fix this query MySQL

We have an extremely large forum running lots of third party software (Most of which doesn't run all that well) and we're starting to optimize things as time allows. This query keeps popping up in the ...
1
vote
0answers
29 views

Resolve “stuck” system process of dropping indexes

I am re-vamping some indexes, and have decided to drop 3 on a certain table. The process has been running for almost 2 hours now. The table does have quite a few million rows, but I still feel that is ...
0
votes
1answer
27 views

MongoDB 'too many indexes' problem

I've got a problem, when I got 6 fields and have no subset of fields, which my app always uses. That means that all of my queries always have different set of fields to scan. Then I read a little old ...
0
votes
1answer
144 views

Hash index for InnoDB

I saw a database schema that looked like this CREATE TABLE foo ( name_hash bigint, name varachar(500), a varchar(500), b varchar(500), ... PRIMARY KEY (name_hash), KEY ... ...
25
votes
1answer
46k views

How to use psql with no password prompt?

I wrote a script to REINDEX indexes in a database. Here is one of them: echo -e "\nreindex for unq_vbvdata_vehicle started at: `date "+%F %T"`" >> ${LOG_FILE} psql -U ${USERNAME} -h ${HOSTNAME} ...
3
votes
2answers
44 views

Poor SELECT performance on recheck cond with data and large (millions of rows) partial index

Query: EXPLAIN (ANALYZE, BUFFERS) SELECT COUNT (*) AS "count" FROM "Posts" AS "Post" WHERE "Post"."createdAt" > '2015-08-19 14:55:50.398' AND "Post"."new" = TRUE; Index: CREATE ...
7
votes
3answers
247 views

Execution Plan is NOT using INDEX, It uses Table Scan

I know when it comes to using an index or a table scan, SQL Server uses statistics to see which one is better. I have a table with 20 million rows. I have an index on (SnapshotKey, Measure) and this ...
2
votes
2answers
252 views

Using the database engine tuning advisor - how do I generate the scripts for the recommendations?

I have run a server-side profile trace for over an hour to produce a .trc file with all activities in one of my databases. I have then passed this .trc trace file as a parameter to the database ...
1
vote
1answer
110 views

Which field should be the candidate for index in this case?

You're tracking visits already in another table that contains quite some information about the visit. In order to block duplicate visits after a certain amount (Let's say 5) you think its best to use ...
1
vote
4answers
243 views

mysql need help optimizing query

I have a table containing servers logs, and another table containing rules to match certain and drop them. The logs tables contains around 1 million rows, and there are about 20-30 rules. The ...
3
votes
1answer
196 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
2answers
2k views

Improve MySQL Query Performance - Too many records

I am using MySQL RDMS for a contact management system. Now a days my database grew in size and contains more than 1 million records. Checking duplicate phone numbers became a big issue during ...
1
vote
1answer
20 views

INDEX size as bytes - PostgreSQL 9.2

Is there any way to get this query to return the index size as BYTES? SELECT relid::regclass AS table, indexrelid::regclass AS index, ...
5
votes
1answer
59 views

Indexes: integer vs string performance if the number of nodes in the index is the same

I hope this is the right place to ask! I am developing an application in Ruby on Rails with the PostgreSQL (9.4) database. For my use case, columns in tables will be looked up very frequently, as the ...
0
votes
2answers
113 views

LOB indexes corruption in Oracle

Why is it not possible to rebuild corrupt LOB indexes? So if my LOB index is corrupted, how to recover it?
3
votes
3answers
117 views

Why SQL Server uses Non-Clustered but not Clustered Index?

I have a table with 145 million rows CREATE TABLE [dbo].[RFTest]( [SnapshotKey] [int] NOT NULL, [SnapshotDt] [datetime] NOT NULL, [LoanNum] [int] NOT NULL, [GLSourceSystem] ...
2
votes
0answers
10 views

In PostgreSQL, can you read from an index during a ALTER INDEX … SET TABLESPACE operation?

I have a PostgreSQL 9.3 server, and there's a large index that I want to move to another tablespace on another disk, because I want to free up space on the original disk. However this is a production ...
7
votes
1answer
144 views

Two columns with and without index in where clause - How index works

I am executing a query on SQL Server 2008: SELECT col1 FROM table1 WHERE col2=val2 AND col3=val3 Here col2 has a non-clustered index, col1 is the PRIMARY KEY, and col3 does not have any index. ...
0
votes
0answers
30 views

SQL Server Index recomended but already there (DMVs)

I am using the DMV views to get a list of index recommendations and then I am reviewing each of them to make sure they make sense and don't overlap etc. Some examples are Index ON X ( Y ) and Table ...
0
votes
2answers
31 views

Index for column with two possible value

I use PostgreSQL 9.4. I have a database where a table have index in column which can contains two possible value only(gender: male/female). When I execute a query with condition on this column index ...