A class of issues where a database executes a query inefficiently due to the optimiser selecting an innapropriate query plan.

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11 views

Optimization suggestions for db2 materialized view

I have a view for db2 9.7 which has consolidated o/p from few tables. The view is built and it is working fine I want optimization suggestions on the view SQL CREATE VIEW XYZZ AS SELECT ...
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14 views

Copying to tmp table slow for query … but only sometimes

I have a query, and I admit it may not be the prettiest query in the world. Sometimes this query runs fairly fast (e.g. 200ms) and other times it runs super slow (e.g. 30s). I don't know why, and ...
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8 views

Design and queries for analysis of event-sequences

I will have to store sequences of events with certain properties in a database (MariaDB preferably) and I have some issues regarding the design and queries. The crucial part is the analysis of the ...
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1answer
48 views

SQL Server sometimes uses a lot more cpu for query

I have a stored procedure with a quite heavy SELECT statement that includes five joins and uses FieldName LIKE '%searchterm%' on multiple columns. This query usually finishes in about 2-5 seconds. But ...
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1answer
51 views

Querying MySQL, duration increases 10x fold after adding one more Join

I have a somewhat complicated query consisting of many joins on an issue tracker/project management database in MySQL. My issue is that my query was doing OK while I was in the process of building it ...
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1answer
47 views

Running a query on an improperly indexed, 600gb table

This is my first post on here and I'm really baffled by this. I have joined a team and somewhere in the past a horrific table was created which has been bloated to a point of 600+gb of data. ...
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1answer
19 views

pt-query-digest results are empty

I have a slow log generated by MySQL 5.1.71-log, that I've copied onto another machine. It appears I'm not getting any results from pt-query-digest. $> pt-query-digest slow.log # 2.1s user time, ...
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1answer
31 views

Simplifying query by adding Computed Column, performance impact?

The dev team came across the following query (might be incomplete; it's retyped from a screenshot) which had caused slowness: SELECT d.catalogno, d.itemid, SUM(lineamount+taxamount) AS Amount, ...
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65 views

SQL Server - Logical Reads lowered, Execution time remained the same

A view executed Select columns from view where col= "date range" (view contains calculation in it Col1+Col2*col3 AS Col4). It took 7 seconds for 500K rows to return, logical reads some 144k. Added ...
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2answers
47 views

Slow fulltext search due to wildly innacurate row estimates

Fulltext queries against this database (storing RT tickets) seem to be taking a very long time to execute. The attachments table (containing the fulltext data) is about 15GB. The database schema is ...
0
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1answer
33 views

Slow response from SELECT query

I have 50 lac rows (i.e. 5 million rows) in student table. I fire select * from student where s_name like('%something word%') limit 0,5. I define indexing on s_name column. That query takes 2 ...
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2answers
221 views

Get table name from union query?

This is my query SELECT Id, productName, Largeimagepath, Discount, Price, Image FROM tablename1 where Active =1 union SELECT Id, productName, Largeimagepath, Discount, Price, Image FROM tablename2 ...
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2answers
167 views

Why can't we access SQL Server when a long query is running in Management Studio?

We have a SQL Server Database (2012 Standard edition). The database is accessed through an ASP.Net web page which displays the count of databases in different tables on page load. This work fine ...
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22 views

My Query is waiting on “db file sequential read” for 5 minutes and getting timeout after that in Oracle

I have a very simple query when I run it individually from the SQL developer in my oracle database it is running perfectly, but when it is part of application flow then it is failing with timeout and ...
3
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1answer
198 views

Optimizing large database query (25+ million rows, using max() and GROUP BY)

I'm using Postgres 9.3.5 and I have a large table in the database, currently it has over 25 million rows and it tends to get even larger rapidly. I'm trying to select specific rows (all unit_ids with ...
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0answers
13 views

mysql update a table from another table - performance

I have two mysql tables, table_A = 2500000+ (rows) table_B = 6000000+ (rows) I need to update rows in table_A from data in table_B (using a multithreaded application) What is the fastest way ...
0
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1answer
68 views

Complicated data

I have a requirement i got from my father. He gave me a table and wanted me to digitalis it. So that he can the system can do all the dirty jobs for him ( that's why there are developers in the world, ...
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0answers
20 views

Query being executed beyond timeout in a transaction Oracle

I have a simple query as below when executed separately the result is coming very quickly. But when is part of the application flow the same query is being shown as in execution status for more than 5 ...
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72 views

Almost identical queries but large time difference in execution

Exhibit A SELECT SUM(value) FROM Credits RIGHT JOIN calendar ON datefield = DATE(FROM_UNIXTIME(created_at)) WHERE confirm = 1 && reason = 1 && country = 'it' && created_at ...
1
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1answer
49 views

PostgreSQL: Another seq scan where an index scan is expected

Here's the query: SELECT DISTINCT ON(points.track_id) participants.contest_number, points.track_id, points.lat, points.lon, points.alt, points.timestamp, points.h_speed, ...
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2answers
72 views

Database SQL Script very, very slow (string manipulation over 700k rows)

I have table containing 700,000 rows containing a string id field with values such as rec-232276-dup-0 and rec-354240-org. The rec- is constant but the other parts of the id can change. I want to ...
0
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2answers
74 views

Find the closest bar, when searching for a drink

Problem: Find the closest bar that serves the drink(s) I'm looking for. Here you can find the generated MySQL code http://pastebin.com/5Uc2ewUW The API Request that interacts with this problem ...
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1answer
65 views

How to increase sql server performance? denormalization (making cascade delete off) vs making duplicate data

I have a database with following related table ( sql server enterptise edtion 2014) each state have many citites which each city has may municpalArea and so on State => Cities = > ...
1
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1answer
47 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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0answers
35 views

Emulating WITH clause in MySQL/query perfomance review

I have never really worked with MySQL queries till this last week. I was tasked with making a simple tool for my department that tracks contacts. Here are the 2 tables and the type of data they ...
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38 views

Slow mysql UPDATE with IF() conditions

not sure why I can't even EXPLAIN this query. Mysql refuses to EXPLAIN it. Table contains a million meaningless test entries. Full schema and data dump of the table available here: ...
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76 views

Memory Issue - SQL Server 2008r2

I am trying to troubleshoot a memory issue on a 2008r2 instance. Very high resource semaphore waits are present and a general slowdown of queries,backups,dbcc checks. Only one instance of SQL Server ...
0
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1answer
65 views

Speed up a MySQL BETWEEN query

SELECT dateToFind FROM table1 INNER JOIN table2 ON dateToFind BETWEEN dateFrom AND dateTo I need to improve the performance of this kind of query. I added BTREE indexes on dateToFind, dateFrom, ...
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32 views

Speed up sorting in this query

I'm trying to optimize the following plan and noticed that PostgreSQL spends a lot of time (relatively speaking) on sorting before the merge joins. Is there a way (using indexes, cluster the table, ...
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4 views

DB2 LUW 9.5 ignoring indexes

OK, Stack Exchange - got another good one for ya'. I am seeing something in DB2 that I’ve never seen before. DB2_VERSION: 09.05.5 AIX VERSION: 7.1.0.0 I’ve got a query that is properly indexed. In ...
0
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1answer
40 views

The materialized view is already optimal and cannot be tuned any further

I have tried DBMS_ADVISOR.TUNE_MVIEW to verify some materialized views created locally. One of the result returns an error: Error report: ORA-13600: error encountered in Advisor QSM-03116: The ...
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2answers
93 views

Is there a more efficient way to run this query for first/max transaction?

For each account, I need the first transaction date, the largest transaction amount, and the time taken to get from first to largest. Data is truncated and reloaded frequently, and I have read-only ...
2
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3answers
115 views

GROUP BY one column, while sorting by another in PostgreSQL

How can I GROUP BY one column, while sorting only by another. I'm trying to do the following: SELECT dbId,retreivalTime FROM FileItems WHERE sourceSite='something' GROUP BY seriesName ...
0
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1answer
44 views

Slow SQL Server authentication, but fast SAN, fast querying?

I am asking you after days of research but I think I don't have required skills to understand what is happening. I have a slow authentication on a SQL Server 2008R2, which leads to a timeout for the ...
0
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2answers
28 views

Best way to store few rows of data every minute without creating 1440 columns a day?

I will be calling a server that returns some JSON data every minute. The values are along the lines of Value, Currency, DateTime, and maybe 1 or 2 more values. What is the best way to keep save these ...
2
votes
1answer
51 views

How to optimise window queries in postgres

I have the following table with approximately 175k records: Column | Type | Modifiers ...
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1answer
20 views

Can having a LIMIT on DELETE degrade performance dramatically?

I have a database project in php and mysql. For, hopefully redundant, data security I added a LIMIT 1 to the delete($uniqueID) php function we use. Nobody cared because records really aren't ...
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20 views

EXPLAIN (with subqueries) is giving results I don't understand

I have a query that relies on a subquery, and that subquery relies on another subquery. When I run an EXPLAIN on the full query, in does a full table scan of the table in the primary select. However, ...
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20 views

Why do these two queries (which I think are equivalent) rely on different keys?

We have a query that we don't like, since it ends up doing a full table scan. EXPLAIN SELECT count(*) AS c, location.name FROM study LEFT JOIN location ON study.location_id = location.id ...
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24 views

Is it best practice to include partition keys within foreign keys when referencing partitioned tables?

The large tables in our database are partitioned by an id in order to separate data and speed up IO. The table of the data is partitioned by the partition key, but the primary key is only on an ...
1
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1answer
76 views

Reducing execution time for this gnarly SQL

I'm creating an order system of some kind. There is a function that I use to get orders (in PHP) and retrieve the required information about the order. However, it seems that I am pulling a lot of ...
3
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2answers
40 views

Why is MySQL ignoring my indexes?

I have a query select distinct id from patient where company_id in (1) and (name_last like 'peter%' or name_first like 'peter%' or remote_id like 'peter%') running on a table that looks like this ...
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60 views

Oracle 11.2 Explain Plan takes too long

I'm using Oracle 11.2 SE on a 16GB Xeon E3 Linux machine as well as 11.2 XE on a 8GB i7 Win8 machine: SELECT banner FROM v$version: Oracle Database 11g Release 11.2.0.4.0 - 64bit Production PL/SQL ...
0
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1answer
41 views

If a query contains two identical subqueries, will they both run?

Say I have a SELECT query that contains two identical subqueries, like the below: SELECT (SELECT SUM(Price) FROM Product p WHERE p.GroupID = g.GroupID) AS 'TotalCost', (SELECT SUM(Price) ...
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0answers
49 views

Slow compilation of a SQL statement

I have SQL Server 2014 and a large table (more than 200Gb) with 100M rows and more than 300 columns. For one "unpivot" query I wanted to see its estimated execution plan and it took more than 90 ...
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1answer
40 views

Tuning Mysql and Monitoring

I would like to know if anybody can point me towards a tool/way for MySQL database tuning ... Actualy the tunning of my.cnf is like below My database is in MyISAM | Mysql 5.1.73 key_buffer = 500M ...
2
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2answers
206 views

UPDATE query with JOIN taking forever

I'm not very good with databases so please keep in mind even if the solution sounds like something everyone would have already tried, please post it because I likely have not tried it and it would ...
0
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1answer
45 views

Does it make sense to order condition in where query?

We have a clustered index in table Tbl with order of A,B,C. Does it make senses to write a query to have WHERE A = @a, B = @b, C = @c or it'll be as same as WHERE C = @c, B = @b, A = @a Does the ...
4
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0answers
47 views

How to handle bad query plan caused by exact equality on range type?

I'm performing an update where I require an exact equality on a tstzrange variable. ~1M rows are modified, and the query takes ~13 minutes. The result of EXPLAIN ANALYZE can be seen here, and the ...
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0answers
53 views

Last few rows from a non-indexed table in Oracle

I'm trying to run a query on an Oracle DB through SQL Server [dont' ask, it's a requirement] The Oracle table in question [lets call it hugeTable] has over 200 million rows and no index. I'm not ...