In the context of a database, optimisation refers to the process of the query optimiser selecting an efficient physical execution plan.

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PostgreSQL 9.1 - Asynchroneous commits performance boost

During peak hours our users experience a lot of timeouts due to an overloaded database server. We are currently trying to make optimizations in order to cope with the high traffic. We read in the ...
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256 views

query optimization delete nested query [closed]

Can the following query be optimized ? DELETE FROM COLOR_TAGS WHERE COLOR_PROJECTID = $id AND NoteID IN( SELECT ID FROM note_note WHERE BibID=$bid AND isdel=0);
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78 views

How can I select data with one query?

I have the following tables: Table xwrh9_betty_dictionary_ids +----+----------+-------+-------------+---------------------+-------+-------+ | id | ordering | state | checked_out | checked_out_time ...
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108 views

How to add an “INCLUDE” part in an Index Created as a part of CONSTRAINT

I am going through the execution plan of a tsql query. There is a key LookUp (Clustered) in the plan. To avoid this Key LookUp, I tried to Include a column (Status_Ind) to The Index (The Index ...
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528 views

Multi-Column Full Text Search Going Very Slow

I have a full text index on a table articles for the columns content, title and keywords When doing the search on each of the columns, like so select count(1) from articles where ...
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67 views

How to optimize multiple ORDER BYs?

I'm getting sluggish performance on a table with ~300,000 rows and B-Trees on each column. This is for a dynamic pagination page where the query is constructed on demand, and the application caches ...
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184 views

How to store temp tables in memory during table “optimize”?

When optimizing tables, SHOW PROCESSLIST lists it as "copying to tmp table". I'm trying to ensure the copy takes place in memory to speed up the process. I've tried adjusting the tmp_table_size to ...
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207 views

Can I rely on this SQL shortcut to save a query?

Consider a table with a status field that holds one of two values: | status | set('active','default') | YES | | active | I need to know how many records are in the table, and additionally how ...
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89 views

DROP TABLE on a huge InnoDB table

I have an innodb table with over 140 million rows taking 26GB. I would like to drop this table however this is taking way too long, probably days. How can I speed up this query? processor: Intel® ...
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89 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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1k views

GUID stored in a varchar field

I have inherited several databases that use GUIDs as PKs. Instead of all the datatypes being uniqueidentifier most are varchar(50) and some varchar(100). Fields are true GUID some where created by ...
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83 views

Need some support on MySQL Query

I have a query SELECT leads.id, sfav.id is_favorite FROM leads INNER JOIN teams tst ON tst.team_set_id = leads.team_set_id INNER JOIN members members ON tst.team_id = ...
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1k views

boolean purpose column char(0) or tinyint(1)

For Boolean purpose column which one is better: nullable char(0) or tinyint(1). I know bool is an alias for tinyint(1) , but in "High Performance MySQL" book that published by O'reilly said: "If ...
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249 views

XML Large DataBase is the best? [closed]

Is the best way to implement a large database is XML? Or is there a better way? 1 - reduce the time complexity 2 - Reduce the amount of traffic between the tables And other factors ... Which ...
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187 views

Is there a way to get slow-query-log-like profiling information on a single query?

Specifically, I'm looking for this information: # Query_time: 0.011922 Lock_time: 0.000088 Rows_sent: 107 Rows_examined: 663 Rows_affected: 0 Rows_read: 107 # Bytes_sent: 4152 Tmp_tables: 3 ...
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141 views

How to restructure this slow query

For the following query: SELECT l.* FROM `leads` AS `l` INNER JOIN `users` AS `u` ON l.client_id = u.id WHERE (`l`.`lender_id` = 1) AND (l.claimed_date IS NULL) AND (`l`.`disabled` = 0) AND ...
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6k views

What would be the fastest approach to bulk update this mysql table (Innodb)?

I have a table with 100M rows. I am able update my table like 850 updates / minute. How to speed this up? I am using following approach: mysql -uroot < query_file where query_file contains 1M ...
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52 views

No value to update but still an TABLE UPDATE Operator

I see this type of code a lot in my databases IF EXISTS(SELECT 1 FROM sample WHERE ID=@id) BEGIN UPDATE sample SET name='cat' WHERE id=@id; END So from my primary analysis it does 2 scan in ...
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80 views

Are nonclustered indexes used when joining tables?

I know that joins of type Sort-Merge don't use nonclustered indexes, because they work by sorting both tables and then joining them. But I've read recommendations to noncluster index all FKs, I ...
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46 views

What would be most elegant way to replicate data contents periodically into a MySQL table?

I need to parse contents from an API route and insert into a MySQL database. The aim of parsing contents is to replicate the data from the API to my database table. I need to check API response every ...
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442 views

MongoDB performance problem

I have a MongoDB for storing result like this {_id, type, imei, lat, lng, spd, dir, time} {_id, type, imei, lac, cid, time} If type is f first one is used and if it is l second one is used. Here ...
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96 views

optimize the query with big and low cardinality

I have big enough dataset and few joins to get them all with help next query: SELECT DISTINCT c.c_id FROM c_active z1 INNER JOIN cs c ON (z1.cv_id=c.cv_id) INNER JOIN indi i ON (c.m_id=i.m_id) INNER ...
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113 views

Postgres: my “data/backup” directory is way too large

In my postgres 9.3 data directory, there exists a subdir called "backup" that is 6.1G compared to my pg_xlog which is only 130M. I understand that pg_xlog is the WAL logs, so what is in the backup? ...
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3answers
622 views

Building A SQL table horizontally VS vertically

What is a better design principle when designing SQL Server tables. One can either add columns (ie grow horizontally) or grow it vertically (ie rather adding rows) I have a situation when there are ...
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273 views

inserting large quantity of data into mysql table

I need to insert about 400 000 000 rows of test data into the InnoDB table. Table is quite simple: CREATE TABLE IF NOT EXISTS `tgt` ( `id_1` int(10) unsigned NOT NULL, `id_2` int(10) unsigned NOT ...
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144 views

What's the best way to translate a website [closed]

I have a website in Django using MySQL, and I have more than 4.000 entries that I want to translate. What's the best way to do it? Create a new database for every language? Create other table for ...
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76 views

Will a specific denormalization increase performance in a specific scenario?

Suppose I have a table with fields | a | b | c | d | ... | z | which contains millions of records and which will serve millions of queries a day. And the field z holds the id of some parameter which ...
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186 views

Need to optimize simple SELECT query for InnoDB table with 2million rows

I'd like to make this query the fastest possible, since it's called really often. SELECT login_events.id FROM login_events WHERE ( DATE(created_at) >= DATE(CURRENT_DATE) AND person_id = 1 ) ...
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2answers
51 views

Convert to JOIN [duplicate]

I have a correlated sub query, which is taking 16 Minutes to execute how can i convert it to join or optimize it. SELECT SSF.SM_StockCode, SSF.ST_ItemSize FROM Stock AS SSF WHERE SSF.SM_StockCode = ...
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68 views

Does limit impact affected rows or not?

I have this table: CREATE TABLE IF NOT EXISTS `usergroups` ( `id` int(11) unsigned NOT NULL AUTO_INCREMENT, `user_id` int(11) unsigned NOT NULL, `group_id` smallint(5) unsigned NOT ...
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3answers
629 views

Table clean up taking too long

I am selecting around 10 million rows which are invalid from table grid into ##grid_temp and deleting their related info from grid_info table. I am running this in a python script. It is taking more ...
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81 views

Query optimization when no row is returned

I am using explain to figure out what is happening in my query which is: explain select t from c where u1_id = 1 group by t; I see "Using where" in the Extra column of the resultset. But this only ...
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89 views

Database and query optimizacion

I have a database containing three tables: tbl_database (main table is the primary), tbl_cmdatabase and tbl_blacklist. The three tables share the same structure but differ in the number of records ...
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74 views

Message system - delete message, or flag for deletion?

I'm wondering, what is the best approach about message deletion in a mysql based message system. Plan A: When the sender sends a message, it will be saved in 2 versions. One for the sender and other ...
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119 views

Does PostgreSQL optimize queries in transaction?

In my app I need to make big imports from user files, and to achieve that all records are updated/created I do it inside transaction. But before it I need to update massive, already existing in DB, ...
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738 views

Slow query with straight_join for small result

I have a performance-problem with a query in my application and I don’t understand the behavior of mysql. The query consists of different joins, especially the join to the mentioncache-table. If the ...
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1answer
95 views

What is the best relationship model for high performance?

I want to model a relationship between Customer and Transaction. However, because Customer is only described by a unique string and no extra info, I have two possibilities to implement it in the ...
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1answer
2k views

Planning simple CMS: How much relation?

I'm currently in the process of designing the database for a rather minimalistic Content Management System I'm working on alone. It should allow scalability while remaining speed, especially on boxes ...
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158 views

Optimizing table and choosing storage engine

Having the follow MyISAM table: +----------------------+-----------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | ...
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102 views

Should I Avoid Repeated References to Aggregate Columns in a View?

So I'm wanting to summarize the balance of the accounts in my business application. My (simplified for our purposes) data model looks like: --Main account table that holds the single accounts create ...
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9 views

Reducing query cache for mostly INSERT-heavy database?

What sort of MySQL query cache should I choose considering the following... Large, rapidly growing database (I got 500,000 rows). UPDATEs practically never happen. SELECTs are rare, but when they do ...
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25 views

Finding the end of a Relationship chain optimally

I have a table that contains an id column, a parent column, and it's child column. So for every record, I know what record comes before it and what will come after it in a chain relationship, but from ...
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48 views

If a database is in memory does it still need indexing?

INFO I'm following lessons on databases. We're learning about indices now. Question If big parts of a table are in the memory, would using a index still have benefits? My side I would assume ...
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59 views

How to manipulate join order of PostgreSQL optimizer?

I am working on table join order optimization. While query processing, I want to get table join order generated by optimizer, and update it by using my own algorithm in PostgreSQL? How can I update ...
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40 views

Speed Up Index Creation in MySQL

In MySQL 5.5, I have a table which is recreated on a daily basis and for which the process of adding an index is taking about 50 minutes which I'm hoping to reduce. At the time when the index is ...
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3answers
131 views

Text Storage and Database Design Optimization in a SQL Server Database

Given a database with a number of columns (c), where some of these columns contain text that is one of multiple values due to a set CONSTRAINT on the columns, what is the most efficient way to ...
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153 views

Database design suggestions for a data scraping/warehouse application?

I'm looking into the database design for a data warehouse kind of project which involves a large number of inserts daily. The data archives will be further used to generate reports. I will have a ...
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353 views

Optimizing GROUP BY Query

I'm running the following query: SELECT `type`, MAX(`time`) AS `last_updated` FROM `stocks` GROUP BY `type` On the following table: CREATE TABLE `stocks` ( `id` int(11) NOT NULL AUTO_INCREMENT, ...
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69 views

index for OR operator with different columns

What would be best index for this kind of query: -- id is the PK create table test3(id number,name varchar2(30) not null,lastname varchar2(30) not null); select id from test3 where id=:1 and ...
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57 views

How can I optimize this query?

I'm trying to select the time field from five tables and return the oldest time. The userid field in every table is indexed. Here's the query: ( SELECT `time` FROM `eventlog` WHERE userid = ...