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

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2
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0answers
54 views

Single table row “sharding/versioning” to customize values

Introduction Hello everyone, I have done quite a bit of searching and I cannot find a solution for my specific issue. There are a few factors that complicate my situation, which I have outlined ...
0
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1answer
20 views

Oracle Autodop disabled at the table level

I have a question related to Oracle auto DOP and parallel DML concepts. I have a scenario, if I set the Auto DOP set to 1 on the table and if I run parallel DML statements on that table through ...
1
vote
1answer
52 views

Poor query performance in MySQL

I have a 10 million record table in a MySQL 5.5 InnoDB. It's running in a 16GB RAM server with good CPU and fast HD. When I run the following query SELECT DISTINCT knowledge_id, ...
0
votes
1answer
53 views

Sql Server Full Backup Duration Increased Dramatically

since last week My Full Backup Increased dramatically .before last week the time is about 3 hour and now the time is about 6 hour.in addition some query take long time to run. (not all the query).I ...
0
votes
1answer
71 views

Slow MYSQL performance due to sub queries

Here is my query: SELECT BAL,NAME, (SELECT SUM(DR) FROM transaction WHERE NAME=TNAME AND DATE < '2000-05-01') AS DR , (SELECT SUM(CR) FROM transaction WHERE NAME=TNAME AND DATE < ...
0
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2answers
58 views

A simple database and Query System? [closed]

I am new to databases and trying to solve one problem in which I have to build a simple database having few entries and then querying that database and then recording that answers from the database. I ...
1
vote
1answer
80 views

Best Indexing Strategy for Query with Equality[A], Range[B], Group By[C], AND Order By[count(P)]

I have a poorly performing query: SELECT user_id, count(item_id) as count FROM table items WHERE category = 'magazine' AND created_at > 1384754400 GROUP BY user_id ORDER BY count(item_id) desc ...
0
votes
2answers
355 views

MYSQL - Why does this SELECT get slower the further down the table?

My table: CREATE TABLE `wp_users` ( `ID` bigint(20) unsigned NOT NULL AUTO_INCREMENT, `user_login` varchar(60) NOT NULL DEFAULT '', `user_pass` varchar(64) NOT NULL DEFAULT '', ...
2
votes
1answer
35 views

General purpose view for last value in a group

I am trying to create a view to show the last value in the group. Looking for a more general purpose query. CREATE TABLE a ( id INTEGER, seq INTEGER, val VARCHAR2(16), PRIMARY ...
2
votes
1answer
79 views

Getting each status change in a table

I have a table that holds status changes per item. The item can go in and out of a status multiple times. ItemTable (ItemId int, Status varchar(50), DateOfChange date) I need to pull the date of ...
1
vote
2answers
106 views

Indexing varchar column to search for first letter

I'm trying to optimize a legacy web-app where users can ask for a list of all records whose name starts with a given character. The query to optimize is: SELECT oggetto.id_oggetto, titolo, anno, ...
0
votes
1answer
45 views

How can I efficiently search for all records from a given month, or a given year?

We have a couple queries that involve datetime fields. In particular, we are checking for things like SELECT field1, field2, ..., field20 FROM table WHERE MONTH(startDate) == 1 SELECT field1, field2, ...
1
vote
1answer
136 views

Slow running query with inner SELECT in where clause

I have a query that looks like the following: USE DATABASE3; GO SELECT t1.COL1 AS COLUMN1, t2.COL2 AS COLUMN2, t1.COL3, t1.COL4 AS COLUMN4, t1.COL5 AS COLUMN5, ...
1
vote
1answer
179 views

How to use LOW_PRIORITY for heavy queries?

I have scheduled heavy UPDATE queries at administrator level, and since they are heavy UPDATEs with multiple JOINs, consume a huge amount of resources. I do not want them to stop end users from ...
1
vote
1answer
681 views

UPDATE a column by COUNT of another table

It might be a naive question, but what is the difference of these two queries and which is preferred? UPDATE table1, (SELECT id,COUNT(*) idcount FROM table2 GROUP BY id) AS B SET table1.Freq = ...
0
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0answers
146 views

Execution time vary for the same query

I have a query which looks like this: select * from ORDERDOC, ORDERPOSITION where ORDERDOC.id = ORDERPOSITION.orderId --some other conditions; Execution plan looks like this: 0 SELECT ...
0
votes
4answers
285 views

Can migration from MS Access to SQL Server or … make database faster? [closed]

A company asked me to migrate their database from MS Access to SQL Server or MySQL because they think that on those engines their database will run faster. But I wonder if their problem isn't because ...
1
vote
1answer
1k views

statistics State in MySQL Processlist

I have a busy MySQL Server having query SELECT sys_sess_state, index_state, timeout_lvl, last_queued_dt, last_polled_wait_dt, create_id, create_dt, modify_id, modify_dt FROM PQR_AM_SYSTEM_SESSION ...
0
votes
1answer
79 views

Is it possible to optimize this query? Or any recommendations to speed it up?

After looking at my mysql slow log file I see that almost every entry there is related to this query: SELECT n.nid AS nid, AVG(v.value) AS rating FROM node n LEFT OUTER JOIN votingapi_vote ...
3
votes
2answers
174 views

Should I add multiple secondary indexes to search

I have a search screen on my app where the users can use up to 4 parameters to search. I have written a stored procedure to facilitate the search. Select ID, FirstName, LastName, ...
1
vote
1answer
77 views

Query tuning - performance

Could you please help me tune this query. It takes over half an hour to run! I want to identify repeat bookings (can only be identified using an annoying varchar field - email) UPDATE #Repeats --a ...
1
vote
1answer
139 views

MySQL: What is the most optimized way to use datetime type field in query

I am working on optimization of some slow queries in my application. I found a query in which datetime comparison has been used. Below is the subquery: select * from jos_content c where c.visible = 1 ...
1
vote
1answer
902 views

Query State hangs on sending data

For some reason, the query state hangs on "Sending Data" (using show processlist;) and I have no idea why. This is the table creating script: CREATE TABLE IF NOT EXISTS `esp_game` ( `gameID` ...
1
vote
1answer
406 views

Using OFFSET in a large table by a simple sub-query

The slow performance for using OFFSET in large table has been widely discussed in various blogs, and the most efficient way is to use an INNER JOIN as SELECT * FROM table INNER JOIN ( SELECT id FROM ...
1
vote
0answers
51 views

join performance, index vs. index+foreignkey

I'm using an orm framework that handles data (and its integrity) on top of mysql. So far I ignored foreign keys because the orm handles that just fine. I recently read that foreign keys can enhance ...
0
votes
2answers
348 views

MySQL: why assign NULL as default value

When we define a table, multiple times we assign default value of a column as NULL. I have How NULL is different than empty value('') as well as 0? Is there any impact of NULL value in query ...
0
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0answers
131 views

MySQL: how to determine key_len and its role in performance improvement of a query

I have a query, below is the structure of the table: CREATE TABLE `jos_tag_rules_fields` ( `id` int(11) NOT NULL AUTO_INCREMENT, `name` varchar(255) NOT NULL DEFAULT '', `label` varchar(255) ...
-2
votes
1answer
96 views

Maximum dataset size for a well-performing SQL Server 2012? [closed]

We're planning a project using SQL Server 2012 for storing about a billion records over less than 50 fields. Assuming good hardware, is SQL Server up to that task? Roughly how many request/second can ...
0
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0answers
59 views

MySQL, query optimization with join on huge table

I'm trying to execute a query on MySQL (Database created from a GTFS schema) I have two tables like these: trips trip_id | route_id --------------------- 1 | 409 2 | 409 3 ...
9
votes
2answers
1k views

Can a single PostgreSQL query use multiple cores?

In recent versions of PostgreSQL, can we share a query between two or more cores to get a performance boost? Or should we get faster cores?
0
votes
1answer
73 views

MySQL: fetch multiple global status and system variable in a single query

When we execute SHOW global status; or SHOW variables; we get list of 291 and 278 records in the resultset. For performance perspective, only few of them are much important. I have to fetch these ...
4
votes
1answer
586 views

Optimising a query against sys.fn_dblog

Looking for assistance improving a query. This query is used to review the last N transactions in the LDF file and then add some useful information like the user, start time, query text, etc.. Here ...
3
votes
2answers
157 views

Query planner thinks doing a sequential scan on a very large table is faster than using an index?

I've got a query that selects the most favorited photo for each of the last 12 editions for a particular domain (this is just a segment of a larger query, but the problem seems to stem from here): ...
0
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0answers
118 views

My SQLs are taking too long to execute for first time everyday in Oracle 11g [duplicate]

whenever I make a new request in my application it takes to long to respond for the first time and all the subsequent requests are faster. If I do it again after some hours or tomorrow again it takes ...
0
votes
0answers
140 views

MySQl: slow query is not using index in joining

Below is the configuration of my DB server: Apache version : Apache/2.2.22 (Win32) mod_ssl/2.2.22 OpenSSL/0.9.8 PHP version : 5.3.13 MySQL version : mysqlnd 5.1.11 Windows Server 2008 Standard ...
2
votes
1answer
212 views

T-SQL Query runs quickly on local PC, but slow on SQL Server?

I have a query with a few joins and a couple of basic SUM(...) statements, and no parameters. It's been running without issue for months - but has suddenly started running very slowly on the server ...
0
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0answers
73 views

Query with large number of or'ed predicates on the same column?

At one place we need to query a table to determine whether any records exists that are in a subset of the same table. The columns that are queried are varchar columns containing file-paths, and we ...
0
votes
1answer
80 views

Sequences Vs Count for auto-increment

Can some one please tell me the exact difference between the following statements , INSERT INTO table1 VALUES ((select count(column-name) from table-name2)+1); here i am using the count function to ...
0
votes
1answer
68 views

Query a name in large database, optimizations? [closed]

if you would like to query a name in a very large database, are there some ways to optimize this query? If 1 million names are in the database, and the name has to stay as it was registered (and not ...
0
votes
0answers
92 views

Postgres chooses a bad query plan

The following query finishes in 1.5s (which is ok, the table contains about 500M rows): explain (analyze, buffers) select sales.* from sales join product on (product.id = sales.productid) join date ...
0
votes
1answer
217 views

Insert but ignore if duplicate AND set a value different if exist in another table

I'm trying my make an invitation system together with the Facebook PHP APK. What I basically want is when you have invited your friends, Facebook redirects back to your website with an array ...
0
votes
2answers
254 views

How to get rid of using temporary when using DISTINCT in MySQL?

When I do the following, I get Using where; Using index; Using temporary. How do I get rid of Using temporary? http://sqlfiddle.com/#!8/f61a2/3/0 CREATE TABLE `test` ( `a` varchar(45) NOT NULL, ...
1
vote
1answer
139 views

Identical query, tables, but different EXPLAIN and performance

I have two tables levels and users_favorites +--------------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | ...
0
votes
1answer
75 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
votes
1answer
64 views

Is it any good for performance to have master and slave on the same server

There are similar questions on this site, but they mostly cover server failure and data backup aspects. I'm concerned only as far as query performance. If master and slave share the same resources, ...
1
vote
1answer
420 views

SQL Server performance for tables having large number of columns [closed]

I have a requirement where I need to create a table with about 600 columns. Out of 600 columns about 200 columns will be XML columns. Other column will be of other datatypes such as int, varchar, ...
1
vote
1answer
133 views

Precautions when designing database schema if tables are going to have billons of rows

I am about to start work on telephone dictionary kind of project. Its confirm that there are going to be billions of records in dictionary table, and each entry from this dictionary table may have ...
1
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1answer
460 views

Large INSERT INTO SELECT [..] FROM gradually gets slower

I've written a program that does a large INSERT in batches of 100,000 and shows its progress. The source table contains 2.5GB of data: CREATE TABLE wikt.text ( old_id INT(10) UNSIGNED NOT NULL ...
15
votes
3answers
762 views

difference in execution plans on UAT and PROD server

I want to understand why there would be such a huge difference in execution of the same query on UAT (runs in 3 sec) vs PROD (run in 23 secs). Both UAT and PROD are having exactly data and indexes. ...
3
votes
1answer
956 views

Comparing two queries in SQL Server 2012

I am comparing two queries in SQL Server 2012. The goal is to use all of the pertinent information available from the query optimizer when choosing the best query. Both queries produce the same ...