In the context of a database, optimisation refers to the process of the query optimiser selecting the best query plan to execute.

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238 views

Why are the plans different if the queries are logically alike?

I wrote two functions to answer Day 3's first homework question from Seven Databases in Seven Weeks. Create a stored procedure where you can input a movie title or actor's name you like, and it ...
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43 views

Tips for improving my particular batch processing

I'm working with mail data from the USPS, which contains 10 related tables to make up a single mailing, as well as a single table containing all of the scans that each mail piece may receive. Once per ...
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1answer
80 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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59 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?
0
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1answer
96 views

On which fields to index? Fields queried (WHERE) or fields returned (SELECT)

I have a large MySQL database table (~1 million rows and growing) on an AWS RDS Medium instance: mysql> describe clients; ...
0
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37 views

How to make a process use all the power of the machine (MySQL process)

I need to do a serious migration of data from MySQL to MongoDB. I have dumped the actual database from its server to the Amazon AWS box. I set up a powerful Amazon AWS Ubuntu EC2 12.04.3 type ...
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1answer
65 views

MySQL geospatial query optimisation suggestions

I am new to DB Administration. Trying to sort out this query which is the heart of our application. I am searching google on similar questions, but would like an experts opinion on my particular ...
2
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1answer
127 views

Optimizing query on a partitioned table

Tried to find an answer for this, but couldn't. So bear with me and apologies if this has been answered elsewhere. It may be just me not being able to find it. Here's the setup: SQL 2008 R2 EE. Table ...
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2answers
55 views

What does enabling containment on server incur?

Having read in a book of Patrick LeBlank "Microsoft® SQL Server® 2012 Step by Step": "Benefits and limitations of contained databases As with most features, there are benefits and ...
9
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3answers
349 views

Optimizing a CTE hierarchy

Update below I have a table of accounts with a typical acct/parent account architecture to represent a hierarchy of accounts (SQL Server 2012). I created a VIEW using a CTE to hash out the hierarchy, ...
0
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1answer
36 views

Oracle sql plan for a select with procedure in terms section

Is there any difference in optimizing a plan to execute any sql request in case of using a procedure from a package which checks to display row or not and in case of constructing a plain sql query ...
6
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2answers
633 views

Adding a Clustered index to a HEAP table on someone else's app

We're using a proprietary application based on SQL Server 2005, which has many HEAP based tables (that is, no Clustered index). Over the years, these tables have grown badly fragmented (e.g. 99% ...
1
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1answer
67 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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2answers
154 views

MySQL (InnoDB) UPDATE SET performance with value in WHERE AND clause

If an UPDATE query is performed where the values being SET are also part of the WHERE clause, in the form of an additional AND statement on the column being set's value, is there a significant ...
3
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2answers
114 views

if database is not shrinked does it affect backup size?

Ok my question is simple. Lets say that when i click database and hover over shrink it says it can be reduced 1 GB space. Now when i do a backup of this database, does this space also getting added ...
5
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1answer
608 views

Schema for analytics table in Postgres

We use Postgres for analytics (star schema). Every few seconds we get reports on ~500 metrics types. The simplest schema would be: timestamp metric_type value 78930890 FOO ...
4
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2answers
810 views

How can row estimates be improved in order to reduce chances of spills to tempdb

I notice that when there are spill to tempdb events (causing slow queries) that often the row estimates are way off for a particular join. I've seen spill events occur with merge and hash joins and ...
0
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1answer
714 views

Optimize MySQL Self JOIN Query

I have a query which is running in 15+ seconds SELECT t1.`ST_StockCode`, t2.`SM_StockCode`, t2.`ST_ItemSize` FROM `stocks` AS t1, `stocks` AS t2 WHERE ...
2
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2answers
113 views

Convert to Self JOIN

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 ...
0
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0answers
30 views

Large-query optimization: given my “explain” results, what stands out?

I've got a monster query, which runs quite quick in many cases, but in some cases very much slower. The EXPLAIN output below is from one of the slow cases. I'm guessing that the slowdown is related ...
2
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0answers
452 views

Query optimization on a large table in PostgreSQL

I am not super experienced with databases, just have a college level course under my belt. I am trying to see if an existing query can be optimized. Currently on average takes over 300ms. There is a ...
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2answers
70 views

SQL Server 2000 optimzation job hasn't run for a while

Our SQL Server 2000 used to run a Sunday morning 3am job of optimizing the database. Somehow it was turned off and hasn't run in a year. We have noticed slow access to the database. We turned it ...
0
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1answer
106 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 ...
3
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1answer
103 views

PL/pgSQL functions and optimizations fences?

I am newbie on DB stuff. And my DB knowledge is very old (around MSSQL2000). All what I remember is, the stored procedures are faster than ordinary queries because it avoid query compilation and ...
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80 views

can this mysql query be optimized further?

I have this query select counterparty_id, max(id) max_id from client_administrations where counterparty_type = 1 and effective_on <= '2013-10-22' group by counterparty_id When I ...
0
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2answers
87 views

Filesort while using primary key for orderby

I have been breaking my head for the past two days now for this. CREATE TABLE `clients` ( `id` int(10) unsigned NOT NULL AUTO_INCREMENT, `guarantor_name` varchar(50) NOT NULL, ...
6
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2answers
294 views

How to optimize NOT IN statement

Why does NOT IN performs INDEX SCAN instead of INDEX SEEK? Here's my current index on the table, CREATE NONCLUSTERED INDEX [idx_dmcasarms_CourseList_cDesc] ON [dbo].[courselist] ( [c_desc] ...
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2answers
49 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 = ...
0
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3answers
147 views

Optimize extremely slow SQL query [closed]

SELECT j.job_id,j.last_updated,j.job_title,j.status, (SELECT COUNT(*) FROM candidates WHERE job_id=j.job_id) resumes_count, (SELECT COUNT(*) FROM candidates c WHERE job_id=j.job_id AND c.ref_type=1) ...
2
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1answer
541 views

How to optimize a query that includes counts of rows in multiple tables?

My query looks like this: EXPLAIN SELECT ... FROM USER u LEFT OUTER JOIN (SELECT COUNT(*) notified_count, user_id FROM user_email_tracking ON u.id = email_tracking WHERE email_type_id = 4 ...
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1answer
143 views

message table schema - body TEXT or varchar [closed]

I want to make a small social network. For messaging body which one is more suitable? VARCHAR or TEXT? if VARCHAR how long is efficient?
3
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1answer
2k views

Slow Queries Not Logging

I am attempting to enable slow query logging on our server in order to identify any queries that could use optimization. Sounds simple enough, however my file is not being written to. I get no errors ...
0
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1answer
793 views

How to measure a perfomance of SQL Server database? [closed]

I have the task to improve the performance of a SQL Server 2012 database (one of 4 in an instance) by 60% confirmed by corresponding statistics. So, I need to measure "performance" of the RDBMS ...
2
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0answers
153 views

How to give permissions to 90+ SQL Servers without tweaking in each of them?

There are over 90+ MS SQL Servers (SQL Server 2005, 2008 and 2012). All in the same Windows domain (but physically all over the world). How to give a domain user (administrative, or other) ...
2
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2answers
120 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 ...
6
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3answers
4k views

Why does MySQL ignore the index even on force for this order by?

I run an EXPLAIN: mysql> explain select last_name from employees order by last_name; +----+-------------+-----------+------+---------------+------+---------+------+-------+----------------+ | ...
0
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89 views

Vertica pagination

I have a query that gives the total number of rows to use in a pagination: select count(1) as total_rows from (subquery with some sum() and 2 inner joins) as as total_sums 1 - when I run only the ...
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1answer
60 views

Do id columns help (in speed) select statements?

I have a table which contains data from aggregation software. The columns mostly are int columns, but three of them are string columns. It looks sort of like: userId, someData1, someData2, ...
0
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1answer
49 views

Join on with modified ON

I am trying to create table with summary of few other tables. All solutions i came up with are very slow and clearly not optimal. Initially I tried with multitude of subquerries but that was very ...
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3answers
128 views

One or several tables for attributes

I just spent some time discussing two alternative DB designs with a coworker and I'm not convinced. Neither of us is strictly DBA so we may be missing something. The overall goal is to create the ...
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85 views

How to index for a group by with columns from different tables?

Is it possible to create an index from columns of 2 different tables? If not, how do we optimize a query that does a group by on columns of 2 different tables? For example: the following ...
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0answers
127 views

Postgres - Partitioning old tables, partition query planning, optimisation

I've been trying to optimise our database, but not being a DBA and not having done a whole lot of tuning before I'm struggling a little with "too many options". I've already run pg_tune and bumped a ...
1
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1answer
64 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 ...
2
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1answer
129 views

Mysql Fragmentation. How bad is too bad?

I ran a table status for my companies production site and its showing close to around '49085939712' for just about every table in my database and we have around 400 tables. I am not a DB ...
4
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1answer
245 views

View with fallback (performance/optimization question)

I have a table with tariffs for stuff; the tariffs table is not important in this scenario, the "tariff values" are. In this Demonstration SQL Fiddle the tariff_plan is the FK to the tariffplans table ...
2
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2answers
468 views

Setting innodb_buffer_pool_size in for Mysql

We have a dedicated DB box with with 8 GB of RAM and running Redhat linux 64 bit OS. Our MySQL Data + Index size almost 7.8 GB. About setting innodb_buffer_pool_size, I have read 2 suggestions Set ...
3
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1answer
393 views

mysql: need help to optimize my query/table

I'm wondering if someone could help me optimize my tables/query to speed up a query. It is currently running ridiculously slow. I think a well-thought out index could help me. Any help would be really ...
0
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2answers
108 views

Help creating this query

I'd like to integrate the following query: SELECT parent.id , COUNT(child.id) AS child_count FROM messages parent INNER JOIN messages child ON child.parent_id = parent.id ...
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47 views

Creating a dedicated HD parition at beginning of disk for data files, benefits and draw backs?

I am thinking of creating a dedicated partition on the harddisk for the mysql database data files in /var/lib/mysql , while considering those 2 points: a dedicated partition will avoid any file ...
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1answer
2k views

Why isn't oracle using an index for distinct query ?

This is the scenario SQL> exec dbms_stats.gather_table_stats(user,'TM', cascade=>true) PL/SQL procedure successfully completed. SQL> SELECT SEGMENT_NAME , SEGMENT_TYPE , BYTES / 1024 / ...