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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1answer
156 views

Sybase ASA: Saving and dropping all foreign keys and most Primary Keys for (Bulk) Insert

Background Information: I am trying to migrate from an ASA 12 Database, to a ASA 12 Database by using a Remote Server. I have to migrate a lot of Rows (not all), spread over a lot of tables (not ...
2
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1answer
126 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(' ', ...
4
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1answer
61 views

When to use sort_in_tempdb when rebuilding indexes?

We are debating whether to use the SORT_IN_TEMPDB option for our DW tables. My understanding is that there are more writes when using this option, although they are more sequential. We have a SAN ...
12
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3answers
1k views

Can spatial index help a “range - order by - limit” query

Asking this question, specifically for Postgres, as it has good supoort for R-tree/spatial indexes. We have the following table with a tree structure (Nested Set model) of words and their ...
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3answers
56 views

Intentionally corrupting an index in PostgreSQL

I need to know if there is any method for intentionally corrupting an index in PostgreSQL. I have been searching for it for a long time but never seen anyone mentioning such an act.
3
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1answer
323 views

Postgres 9.3 - deletes terribly slow for 10 minutes after dropping indexes/constraints

If I run a script which drops indexes (17 of them, CONCURRENTLY makes no difference except that without it I get the occasional deadlock), then constraints (20 constraints on 18 tables) and then run a ...
3
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1answer
30 views

Guidelines for full-text index maintenance

What guidelines should be considered for maintaining full-text indexes? Should I REBUILD or REORGANIZE the full-text catalog (see BOL)? What is a reasonable maintenance cadence? What heuristics ...
2
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1answer
44 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
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1answer
127 views

Dropped Index during Database Engine Tuning Advisor

I was analyzing a query using "Database Engine Tuning Advisor". During this time the database started to get blocking, long running queries and ended by restarted the instance. When I checked after ...
3
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1answer
33 views

MySQL query WHERE IN + ORDER BY, which EXPLAIN is better and how to avoid filesort?

This is my table definition, without any special index for now: CREATE TABLE `filter` ( `field_name` varchar(32) COLLATE utf8_unicode_ci NOT NULL, `category_id` varchar(32) COLLATE ...
6
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1answer
268 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 ...
0
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1answer
46 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, ...
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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 ...
0
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2answers
39 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?
2
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1answer
29 views

Non clustered index for non-evenly distributed data in large SQL table

I have the following table containing 2.000.000.000 rows: CREATE TABLE [VeryLargeTable] ( [dataCol1] [NVARCHAR(MAX)] , [dataCol2] [NVARCHAR(MAX)] , [Manufacturer] [NVARCHAR(10)] , ...
0
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1answer
33 views

Custom big key-value database indexing [closed]

I want to make a key/value database with millions of records. A custom-length unique UTF-8 text will be used as key 16 unique bytes will be used as value What is the best way of storing this ...
1
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1answer
52 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), ...
3
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2answers
102 views

SQL server tools to identify query optimisations and missing indexes [closed]

I have a broad question regarding SQL Server that was given to me on a quiz and I am not sure what the answer is as I do not have access to SQL Server at home. My question is how can I utilise SQL ...
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5answers
19k views

Index Seek vs Index Scan

Looking at an execution plan of a slow running query and I noticed that some of the nodes are index seek and some of them are index scan. What is the difference between and index seek and an index ...
4
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1answer
76 views

PostgreSQL partial index unused when created on a table with existing data

In PostgreSQL 9.3, I am attempting to create an efficient index on a rarely-used (0.00001% of total records) boolean column. To that end, I discovered this post on SO: ...
25
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4answers
20k views

When should I rebuild indexes?

When should I rebuild the indexes in my relational database (SQL Server)? Is there a case for rebuilding indexes on a regular basis?
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1answer
30 views

Database index on FK with only NULL values

We have in our database an index with table cardinality over 10.000 but full key cardinality only 1. The reason for this that all the values for the column are NULL, hence cardinality 1. Does this ...
0
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1answer
29 views

Which are the differences and advantages on single INDEX or compound INDEX?

I have two INDEX on a n:m relationship table as you can see on pics below: Now I can have this also: My questions: What is the advantage from last way(pic compound) over the two first? Can ...
1
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1answer
23 views

Rename PK column names when they are FK in another tables

I need to change the names on PK columns and that has relations with another tables meaning they are FK also so this is what I am doing: SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0; SET ...
0
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2answers
20 views

Separate indices for the field I want to get the MAX() and the ones in the WHERE clause

My customer's database has a gigantic table (hundreds of millions of records) and a SELECT that, by cumulative use, is eating a huge chunk of processing time. Each exec takes almost a minute in ...
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0answers
25 views

Speeding Up Query - Hangs at Sending Data - Indexed Correctly

I am looking for ways to speed up the below query. I currently have indices on FIRST, LAST, UNIT_PARENT, HomeAddressLine1, HomeAddressLine2, HomeCityNAme, HomeStateAbbreviation, HomeZipCode, HomeZip4, ...
5
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3answers
209 views

Postgres is performing sequential scan instead of index scan

I have a table with about 10 million rows in it and an index on a date field. When I try and extract the unique values of the indexed field Postgres runs a sequential scan even though the result set ...
3
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1answer
54 views

Finding optimal indices, different query competing indices

My schema: create TABLE "logs" ( "id" serial not null default nextval('logs_id_seq'::regclass), "request" varchar(1024), "token" varchar(512) default NULL, "was_batch_request" bool ...
1
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0answers
44 views

Database fragmentation and heap SQL Server

We have critical performance issues with our production database (its around 300 gb size) We have run the following script for a few huge tables : DECLARE @db_id SMALLINT; DECLARE @object_id INT; ...
0
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1answer
144 views

Use index intersection feature in mongo 2.6 to compound shard key

I am having three indexes like name,age,salary. I can use them as compound index as per 2.6 (name and age together). But can i use the same indexes as compound shard key like name and age. i also have ...
3
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0answers
35 views

type ALL in explain [closed]

I have tables like these: items +-------------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | ...
8
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1answer
258 views

Why would function based indices I’ve created lower the cost but not show up in the explain plan breakdown?

Sorry for the terrible column/table names but since this is for a work project I wanted to insure it was OK to ask. I was just hoping to at least learn why I'm not seeing my functional indices being ...
6
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2answers
153 views

Optimizing WHERE condition for TIMESTAMP field in MySQL SELECT statement

I am working on a schema for an analytics system which tracks usage times, and there is a need to see total usage time in a certain date range. To give a simple example, this type of query would be ...
2
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1answer
309 views

Check if an index exists by comparing columns

We are currently using ALL_IND_COLUMNS to check if an index exists by its name or the columns it is using. The problem is that we can only check if the index exists with columns in a specific order. ...
2
votes
1answer
446 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 - ...
9
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2answers
269 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 ...
0
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2answers
544 views

Run query faster, what index to use

I have a table with 85M rows : CREATE TABLE emissions_totales ( "schema_source" varchar(150), "snap" varchar(20), "gid" varchar(255), "polluant" varchar(50), "emi" float8, "numreg" varchar(3), ...
1
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1answer
27 views

Using a GIN index on an integer array to model sets of tags

In PostgreSQL, what are the pros and cons of using a GIN index on a column of type integer[] to model sets of tags, instead of doing a relation table? I am trying to design a simple data model with a ...
3
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1answer
88 views

To have PostgreSQL-like Partial Index in MySQL 5.5

I have big data where I only select a small interval of data at a time such that the selection is always in a sequence. I am trying to implement PostgreSQL like Partial index in MySQL which is ...
0
votes
1answer
180 views

MySql: Slow join and group by on indexed columns

The following query takes 15-20s to run SELECT "Trade_US"."ID" AS "Trade_US.ID", "Server_US"."Name" AS "Server_US.Name", "Trade_US"."TradeTypeID" AS "Trade_US.TradeTypeID", "Users"."ID" AS ...
2
votes
1answer
65 views

Multiple indices on a table

I have run SQL Profiler and I can see that I'm "missing" some indexes (non-clustered) on a table. How is it best to handle indexes that can be a "subset" of another index? Index 1 UserId, ...
2
votes
2answers
26 views

Indexing order by columns

Based on the query below it was suggested that I create an index on the column in the order by clause. My understanding is the sorting is done on the result set and not the table. The person ...
2
votes
2answers
169 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 ...
0
votes
1answer
45 views

How to manage RAM consumption in MongoDB?

I am using MongoDB. I have a hardware device which continuously submits data to the database every 10 seconds for 4 hours a day. The data includes latitude, longitude, and other basic information of ...
1
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2answers
86 views

Add UNIQUE index fails with duplicate entry error, but no duplicates found

Given table: CREATE TABLE mytable ( field_a CHAR(15) NOT NULL DEFAULT '', field_b MEDIUMINT UNSIGNED NOT NULL DEFAULT 0, field_c SMALLINT UNSIGNED NOT NULL DEFAULT 0, field_d SMALLINT ...
0
votes
1answer
138 views

When to use hashtable over binary search tree vice verse for Database Index

Database Index can be constructed using binary search trees (BST) or HashTables , From my understanding so far , HashTables are superior to BST in terms of time taken for searching and insertions ...
5
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2answers
104 views

“Recheck Cond:” line in query plans with a bitmap index scan

This is a spin-off from comments to the previous question: Postgres 9.4.4 query takes forever Using PostgreSQL 9.4, there always seems to be a Recheck Cond: line after bitmap index scans in query ...
12
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1answer
6k views

Index optimization with dates

I have a large table of objects (15M+ row) in PostgreSQL 9.0.8, for which I want to query for outdated field. I want to divide the query by millions, for scalability & concurrency purposes, and I ...
2
votes
2answers
65 views

Fulltext search using multiple indexes

I have a table with several columns, say a, b, c, d that should be searchable. The problem arises when I need to search a, b, c separately from d (and vise-versa). AFAIK, there's no way to achieve ...
1
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1answer
804 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? ...