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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1k views

mysql “Lock wait timeout exceeded” two transaction with different keys indexed

I have set of tables that I need to delete their records with a specific key and insert new records. Different transactions are used one for each key: Transaction 1: DELETE FROM table1 WHERE id=1; ...
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1answer
103 views

Constrain exclusion to fetch latest N rows

I'm managing a table with several million records which are being inserted in real time. A part of my app needs to display the last N inserted records, so at the beginning I just queried for: ...
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1answer
74 views

When is the index actually created?

I have noticed that even on huge tables with millions of records when I do a CREATE INDEX the index is created immediately (I get the console back in nsecs). Why is this? Doesn't it create the B-Tree ...
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1answer
1k views

Postgresql indexes in memory

I use Postgresql 9.2. I have tables stored on a ramdisk, but now indexes on those relations are located on a regular disk. I want to move them into ram too, but for all I know postgresql loads indexes ...
2
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1answer
266 views

Implications of a second index on a timestamp field in a sequential table

I have a MySQL table of a few gigabytes with roughly ~100M rows. I store data sequentially, such that the timestamps increase as the ID also increases. Because ordering and filtering by the timestamp ...
2
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1answer
656 views

MySQL InnoDB issue not using indexes correctly [Percona 5.6]

I just installed Percona 5.6 on my new CentOS 6.4 server. It's a fast machine 32 core xenon, 72GB ram, 8x SAS RAID 10 setup. So far so good My old server is a bit less powerful, and was running ...
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1answer
136 views

What is the structure that SQL Server uses to build and maintain indexes called?

What is the structure that SQL Server uses to build and maintain indexes called?
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1answer
83 views

Why add indexes to these columns in the Database?

I am trying to get my head around this code. It's from the Rails Tutorial Book and is part of the process of making a twitter like application. class CreateRelationships < ...
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0answers
21 views

Why is SQL Server Recommending I Create this Index? [duplicate]

I have the following query: Select SubId, Max(ReadTimeLocal) From dbo.PanelWorkflow Where ProcessNumber IN ...
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1answer
57 views

Creating an index on table A but with reference to table B

Our company uses a 3rd party application for numerous aspects of the business. One aspect is dealing with customer payments and when selecting a window within the app to list all the payments ever ...
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1answer
90 views

How is the number of records on a select determined as high or low by optimizer?

What is the threshold between using the index and doing an direct access to the database? I assume this decision is related to the number of index access (and subsequent access to the tables). If this ...
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2answers
311 views

What can be done to further enhance performance of Multiple Join and Aggregate Queries?

I have a typical star schema simulated here, and I am mentioning two queries: first query simply joins the fact table with 2 dimension tables and 1 calendar table, and the second query joins and ...
1
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1answer
78 views

Mysql with index [closed]

I have this following sentence: SELECT Day(C.DataCadastro) AS Dia, Month(C.DataCadastro) AS Mes, Year(C.DataCadastro) AS Ano, COUNT(I.Plano) AS Total FROM clientes AS C ...
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1answer
69 views

Query when index is ready

To improve performance of a query I set up an in-memory table and fill it with data. Of course to increase speed I will use an index on the data stored in the in-memory table. create table helper ( ...
0
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1answer
66 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 ...
18
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2answers
2k views

Index not making execution faster, and in some cases is slowing down the query. Why is it so?

I was experimenting with indexes to speed up things, but in case of a join, the index is not improving the query execution time and in some cases it is slowing things down. The query to create test ...
0
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1answer
287 views

How can I speed up a DateTime comparison query in MySQL?

I am performing the following query on a MySQL table with around a million records ( ~350MB ). It takes roughly 1.5 seconds every time. If I remove the OR last_updated > last_geocoded comparison, ...
2
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1answer
201 views

How efficiently does iSeries DB2 use index with WHERE <>?

MS SQL dev here, this is my first attempt to optimize a DB2 query on iSeries. I was asked to help improve a huge query which consists entirely of dozens of joined subselects. Some of those subselects ...
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1answer
384 views

Using coalesce on an index column

Does doing a COALESCE on an indexed columns in a WHERE clause e.g. WHERE COALESCE(table1.indexed_column, '9999-01-01') > table2.other_date_column affect indexing in a bad way? I think that it ...
0
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1answer
218 views

SQL Server Index Scan Actual Executions

I have a fairly complicated query and running it on two databases with same schemas, but with different data produces different result. On database D1 the elapsed time is around 1 second, and the ...
2
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1answer
220 views

Find statements related to sys.dm_db_missing_index… tables (SQL Server)

I have read up different articles related to SQL Server 2008 on how to find out missing indexes using the tables sys.dm_db_missing_index_groups, sys.dm_db_missing_index_group_stats etc. One thing ...
0
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1answer
155 views

Best read performance when every query is known, and the data doesn't change

I'm trying to maximise performance on an underpowered PostGIS server - 1 core, 4 CPUs. The data (OpenStreetMap) will be infrequently (monthly?) loaded, and never changes otherwise. Each of the 30 or ...
3
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2answers
1k views

MySQL - Add index to low cardinality text column?

I'm working on project where an enum column is being converted into a text column (I cannot change this). The cardinality of the column is low (7 unique values). Would I gain a performance increase by ...
2
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1answer
327 views

How to repair all indexes in a MySQL database?

My database got corrupted, and now the php app is throwing this error: Invalid query: Can't find FULLTEXT index matching the column list The error is not very useful, since it doesn't say what ...
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3answers
2k views

Index on Persisted Computed column needs key lookup to get columns in the computed expression

I have a persisted computed column on a table which is simply made up concatenated columns, e.g. CREATE TABLE dbo.T ( ID INT IDENTITY(1, 1) NOT NULL CONSTRAINT PK_T_ID PRIMARY KEY, A ...
3
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2answers
166 views

Query has where (a = a) or (b = b) - the 2nd part causing index scan. Full example included

I've been trying to figure out why this query (on integers) is using an index scan when both values (the original table, and the table its looking up in) are integers. The first part is used to fill ...
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4answers
3k views

How to find index organized table

I'm working on Oracle 11g database and I need to list all index-organized tables. Is there a dba's view to query for that ? Thanks
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2answers
9k views

Efficient query to get greatest value per group from big table

Given the table: Column | Type id | integer latitude | numeric(9,6) longitude | numeric(9,6) ...
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0answers
444 views

Using an enum as part of an index definition

When I use an ENUM column in a table the ORDER BY uses the ordinal of the ENUM not its value. I wasn't aware of that. So my question is what are the subtle issues when an ENUM is part of an index ...
4
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1answer
1k views

Advisability of using STATISTICS_NORECOMPUTE

I've recently become involved in maintaining a set of databases with some interesting index problems. One of the ones that aggravates me the most is the differences in the indexes between ...
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2answers
54 views

same field in bothe “where” and “order by” - how to index for this query?

The query: EXPLAIN EXTENDED SELECT *, u.user_id FROM xgate_geoloc g JOIN tig_users u ON g.uid = u.uid WHERE -- corners selection: ( ( ...
0
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3answers
833 views

Performance of primary key IDs with gaps (but in sequential order)

I know that having non-sequential IDs is bad for index performance. But assuming all my IDs are created in correct order, but with large gaps: i.e: 154300000 283700000 351300000 464200000 ...will ...
3
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1answer
6k views

MySQL requires FORCE INDEX on huge table and simple SELECTs

We have an application which stores articles from different sources in a MySQL table and allows users to retrieve those articles ordered by date. Articles are always filtered by source, so for client ...
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806 views

MySql INNER JOIN doesn't use composite index

I have two tables, table A which contains date and name of table B entry and table B which contains its name and type. Table a has a composite index on table_b_name and date. I'm selecting all table A ...
3
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1answer
557 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] ( ...
2
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1answer
951 views

Does MySQL reindex on update

I have a users table with various fields which are getting updated frequently. i.e table have: userid - PRIMARY int profile_views - int ratings - int last_active - int ( to store UNIX timestamps for ...
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0answers
143 views

Error creating spatial index sqlserver

I am creating spatial index on sqlserver table. CREATE SPATIAL INDEX [SIndex_udt_cell_SP_GEOMETRY] ON [udt_cell] ( [SP_GEOMETRY] )USING GEOMETRY_GRID WITH ( BOUNDING_BOX =(80.0713, 26.389581, ...
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0answers
778 views

Is it possible to optimize a range query so an explain statement would state “using index” instead of “using index condition”?

I have a very large table where specific queries made by my application are timing out. The table looks something like this: LargeTable ------------ Id [BIGINT(20)] UtcTimestamp [BIGINT(20)] Pivot ...
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1answer
195 views

How to minimize the need for recalculating index on SQL Server?

We have rather big tables (500 mils rows) where we expect frequent inserts. The tables have approx. 2 indexes each. The problem is that we are afraid that, when the index is recalculating the whole ...
2
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3answers
119 views

Are these indexes redundant?

I have two indexes on a table that will contain roughly 10-20 million records at a given moment. Index 1 CREATE NONCLUSTERED INDEX [IX_NC_AccountNumber_UTC] ON [dbo].[LogWindow] ( ...
0
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2answers
92 views

Rebuilding index

I have a transaction database and one of nightly job is to rebuild indexes that followed by a log backup and then shrink the log. Is this safe to do so ? Thanks Antony
0
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1answer
36 views

I have to create INDEX but which? [closed]

I have to create INDEX but which with this query ? SELECT * FROM TABLE WHERE A = 1 AND B = '5427dbfac0a8280d74bc672c72636a4f' AND C = 'BIL' AND D = 'B' and E = '01' GROUP BY F,G,E,H,I ORDER ...
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2answers
143 views

Fill Factor Setting and Performance

From what I've read, typically for indexing the recommendation is to leave the fill factor at 70-80, and the logic behind this seems that new data may be inserted into a table between existing values ...
3
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2answers
5k views

MySQL not using indexes when joining against another table

I have two tables, the first table contains all articles / blog posts within a CMS. Some of these articles may also appear in a magazine, in which case they have a foreign key relationship with ...
0
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1answer
134 views

Using an enum index to limit records

A common issue, just not sure on the keywords. I have a table of assessments (14k+ records). Each assessment can be in many different states ('draft', 'proofing', 'amends', etc... and 'done'). Most ...
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0answers
4k views

How to speed up query on table with millions of rows

The Issue: I'm working on a big table that consists about 37mln rows. Data include measurements of many devices made in certain time e.g. '2013-09-24 10:45:50'. Each day all of those devices are ...
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1answer
58 views

Creating Multiple Indexes on SQL Server [closed]

I am creating multiple indexes on a table in SQL Server. The script is still executing but all the required indexes are showing as objects in Object Explorer. Do the objects get created before the ...
3
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2answers
10k views

What is difference between primary index, secondary index, unique index and normal index?

I work on Oracle systems where I two type of indices exists in any table: Unique index (Based on any search key which is unique key). Normal index (Index made on any search key which is not ...
0
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1answer
90 views

How to store values of all columns in an index in PostgreSQL?

As described here: https://devcenter.heroku.com/articles/postgresql-indexes#managing-and-maintaining-indexes indexes do not store the entire row data themselves. Is it possible to store the whole row ...
2
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2answers
131 views

Optimize query or model, to get an population overview in time

I think I've got a very simple model and query, but I cannot find a way to make use of indexes to boost performance. I wonder if there is a trick in my model, or MySQL query, to speed up the ...