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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2answers
635 views

Adding index to large mysql tables

I have a table | base_schedule_line_items | CREATE TABLE base_schedule_line_items ( id int(10) unsigned NOT NULL AUTO_INCREMENT, installment int(10) unsigned NOT NULL, on_date date ...
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0answers
54 views

is it good to add index on column used in group by clause?

I have a query like- select x, sum(y) from xyz where z>=100 group by x order by sum(y) desc; will it be faster if I am going to add index on x?
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0answers
50 views

Group by clause giving temporary and filesort

I am using this simple select query which selects data from table inner joins and using group by clause. Here is the query ..I have defined indexes for the where clause and group by clause. But some ...
5
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1answer
297 views

Don't rebuild indexes < 1000 pages - then why bother having them?

Microsoft recommends not bothering to rebuild indexes that have less than 1,000 pages (from memory I think it's because they are so small that they will be held in RAM). If I'm not rebuilding them, ...
9
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3answers
179 views

One index or two?

I have the following index created on a table in my database: CREATE INDEX [idx_index1] on [table1] (col1, col2, col3) The server is suggesting the following 'missing' index: CREATE INDEX ...
0
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1answer
80 views

Index being ignored by Oracle

I have a table for sensor data, simplified it looks like this: DEVICE_ID NUMBER SENSOR_ID NUMBER DATA_TIME NUMBER DATA_VALUE1 NUMBER The table constains billions of rows and is partitioned by week ...
0
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2answers
143 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 ...
4
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1answer
755 views

Why would you index text_pattern_ops on a text column?

Today Seven Databases in Seven Weeks introduced me to per-operator indexes. You can index strings for pattern matching the previous queries by creating a text_pattern_ops operator class index, as ...
2
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1answer
585 views

Need for indexes on foreign keys

I'm struggling with indexes, primary keys and foreign keys... And the need of having them all. If I have two tables, both of them have an integer as a primary key. The first table references ...
0
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1answer
86 views

Which index types do not support online index rebuilds?

In SQL Server 2012 Enterprise Ed., which index types do not support online index rebuilds? and why? and which activity-operations can prevent online index rebuilds?
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1answer
225 views

What is blocking 'SELECT… WITH(NOLOCK)'?

While following BrentOzar's "How Much is Offline During an Index Rebuild?" I was curious to run: SELECT Quantity FROM [Production].[TransactionHistory] WITH(NOLOCK) while executing a rebuild ...
0
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1answer
84 views

Oracle 11g INDEX_SS Hint

Given a table with columns A, B, and C of type CHAR(15) and an unique index If I have a query with a WHERE clause specifying A and C, oracle's optimizer chooses to do an index range scan. But if I ...
2
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1answer
451 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; ...
0
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1answer
67 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: ...
1
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1answer
62 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 ...
0
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2answers
504 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
votes
1answer
150 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
votes
1answer
310 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
112 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
77 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
19 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
55 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 ...
0
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0answers
61 views

Understanding how MySQL indexes work

I'm reading this page but I can't get past the following parts: When all tables are processed, MySQL outputs the selected columns and backtracks through the table list until a table is found ...
0
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0answers
89 views

How does MySQL handle an index if its full size is too large for memory?

Let's assume this (totally artifical) query: select id from T where id%3=0 order by id desc; The index of T (InnoDB) is according to information_schema.tables sized 5 GB and T itself is 3 GB but ...
1
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1answer
76 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 ...
2
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2answers
159 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
76 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 ...
0
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1answer
47 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
54 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 ...
17
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2answers
894 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
158 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
votes
1answer
112 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 ...
1
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1answer
185 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
100 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
116 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
134 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 ...
2
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2answers
585 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 ...
1
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1answer
161 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 ...
17
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3answers
815 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
votes
2answers
126 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 ...
2
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4answers
950 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
5
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2answers
2k 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) ...
0
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0answers
203 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 ...
3
votes
1answer
384 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 ...
0
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2answers
48 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
votes
3answers
410 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 ...
2
votes
1answer
2k 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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0answers
323 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 ...
2
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1answer
240 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
574 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 ...