An evaluation of whether a system works well enough to be fit for purpose. Normally performance refers to the speed with which a system completes an operation or set of operations over time.

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3answers
653 views

MySQL: How to avoid case sensitivity in SQL queries when migrate from Windows to Linux?

I have migrated my Database from Windows to Linux server. In many places, query has been written without focusing their cases (uppercase / lowercase). So, these queries are not getting executed and ...
4
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0answers
123 views

Timestamp-based index

I have a big database (200GB+) that contains some log info. And I want to speed up SELECT queries and stored procedures. I have a table with a GeneratedOnUtc datetime column, and have a non-clustered ...
0
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0answers
33 views

redshift performance effect if use 32 character long unique string as Primary key instead of auto incremented int

In my analytics application I am creating 32 char long unique string for each hit as user_session. In current implementation, I am storing user_session in tbl_sesssion in session column and I am ...
2
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1answer
82 views

Oracle 11g connect overhead

Currently one of our new applications is connecting to an Oracle 11g instance over 30,000 daily (at every user request) via their application server, using the same account. (it will be significantly ...
0
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1answer
44 views

Improving lots of Left Joins ( SQL Server 2008 - procedure )

This query is running with 8 minutes to complete. I'm trying to help the programmer with this task. I've created indexes and stats, update_stats and rebuild indexes but none of this is helping us. ...
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0answers
36 views

Multiple subqueries performance issue

I have a query that collects customer data. I select a lot of correlated data from different tables. I want to have only ONE result row for each customer. The query looks like that: SELECT c.Id ...
0
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1answer
30 views

Reusing covering index for fields in FROM, from another query's index

For the following query I have a covering index as so: SELECT bar_id FROM foo WHERE user_id=:user_id AND date_sent=:date_sent; ALTER TABLE foo ADD INDEX (user_id, date_sent, bar_id); Now I have ...
1
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1answer
108 views

Query on 250 million records

I have a table with below structure CREATE TABLE [dbo].[ColumnValues]( [Id] [int] IDENTITY(1,1) NOT NULL, [ColumnId] [int] NOT NULL, [Value] [nvarchar](max) NULL, [OutputArea] ...
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0answers
57 views

PostgreSQL Performance - Many Large Databases

I run an internal (development) database server containing 25 databases each ~71GB in size. There are usually between 50 and 100 active connections at any given time. What can I do to help improve ...
2
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1answer
40 views

io_stall question

I just installed SQL Server on new hardware and ran a test script to show io_stall information by file. Nothing else has been loaded yet, just a fresh install of SQL Server 2012. Why are the ...
5
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1answer
3k views

SELECT with large WHERE IN clause taking long time

I'm pretty new at all this so be gentle :). I have large medical DB where I need to extract data for patients based on selected doctor(s). Right now I build a patient list by SELECT patID FROM ...
0
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1answer
36 views

Query running slow on script and producing error 500 when run in phpmyadmin

I have a query that seems to take a good 30 seconds to execute even when the query produces no results. There are 4000 lines within the database and queries that produce all results run within ...
1
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2answers
188 views

OLAP or OLATP - How to determine

I have SQL express server with database that is used by one application. I am trying to optimize the DB but am not sure if the DB is OLTP or OLAP. There is no analysis server installed, the DB is ...
0
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0answers
29 views

Performance/Maintenance Implications of a Write Heavy Table In An Otherwise Normal “CRUD” Database

We have a small-ish (<100,000 rows) MySQL database (on Amazon RDS). Its supporting a fairly simple read heavy CRUD web application. Currently we're building out a web analytics system. It will ...
22
votes
4answers
22k views

Pattern matching with LIKE, SIMILAR TO or regular expressions in PostgreSQL

I had to write a simple query where I go looking for people's name that start with a B or a D : SELECT s.name FROM spelers s WHERE s.name LIKE 'B%' OR s.name LIKE 'D%' ORDER BY 1 I was wondering ...
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2answers
1k views

How to fix slow LIMIT queries with big offsets without heavily rewriting them?

Imagine a very basic example of your average discussion board. For example: CREATE TABLE threads ( id INT UNSIGNED NOT NULL AUTO_INCREMENT, title VARCHAR(100), PRIMARY KEY (id) ) CREATE ...
11
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4answers
6k views

What's better for large changes to a table: DELETE and INSERT every time or UPDATE existing?

I am making a project where I need to change around 36K records in one table daily. I'm wondering what will perform better: delete rows and insert new ones, or update already existing rows For me ...
0
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0answers
61 views

SELECT query on mySQL taking 20 seconds to execute

Many points to note: This SELECT statement is happening both on my site, terminal, and on phpmyadmin, so the problem isn't a coding problem. If you delete the 11,000,000 rows and keep 20,000 rows ...
6
votes
1answer
514 views

Would index lookup be noticeably faster with char vs varchar when all values are 36 chars

I have a legacy schema (disclaimer!) that uses a hash-based generated id for the primary key for all tables (there are many). An example of such an id is: 922475bb-ad93-43ee-9487-d2671b886479 There ...
4
votes
1answer
557 views

SQL Server 2012 Local SSD TempDB Slow

I have a production deployment using local SSDs for tempDB. I have 2 SSDs in a RAID1 configuration. I am seeing average reads of 1-2ms but the average writes are showing as 1377ms on all four of my ...
3
votes
2answers
90 views

When does SQL Server determine to use a new index?

I have been performing some maintenance on a server that runs some software the company bought, so I can't really change how the queries have been written. I have used some tools to determine some of ...
0
votes
1answer
78 views

MySQL performance of applying unique constraint single column vs combination column

I have a large MySQL InnoDB table containing around 137 million rows. I need to add a unique constraint to the table. We have two options: 1) A combination index on three columns, one of which will ...
2
votes
1answer
109 views

Optimise huge Postgres table for fast read

I'm about to create a Postgres table with 1.5 billion rows. The table will just have a single TEXT column. The table is effectively a blacklist. When a user of my software saves certain data, this ...
1
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2answers
1k views

How to “warm up” a cold DB server?

1st setup was a DB slave that was used by customers. That was sufficiently fast. 2nd setup (now) is replication of a DB slave that is just used by me. The current setup is slower on query execution ...
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0answers
103 views

Excessive CPU Usage caused by long running query?

We have been getting intermittent excess CPU usage at 100%. There is not a whole amount running on the system. We also get warning of Batch Requests/sec above threshold.: 1030, which would seem to ...
1
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2answers
145 views

Oracle nologging impact for REDO Generation

Oracle database is on noarchivelog mode and tablespace is configured with nologging option keeping there will not be a situation to recover any data in mind. Following scenario was occured during ETL ...
6
votes
2answers
7k views

What's the difference between POINT(X,Y) and GeomFromText(“POINT(X Y)”)?

I'd like to store some geometric positions in my MySQL database. For this I use the POINT datatype. Almost everywhere I read that the function GeomFromText should be used to insert data in the table. ...
1
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1answer
137 views

What does a “Buffer cache hit ratio” of 9990 mean?

I got this query from a blog post: SELECT object_name, counter_name, cntr_value FROM sys.dm_os_performance_counters WHERE [object_name] LIKE '%Buffer Manager%' AND [counter_name] = 'Buffer cache hit ...
1
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0answers
30 views

Replication / Bulk Update between Servers

I'm looking to update several tables between two servers daily to have a replica of the data available. My question is, what is the least resource heavy and most effective method to implement this? ...
0
votes
1answer
238 views

Compare two big tables in PL/SQL

I need to implement comparing 2 tables by set of keys (columns of compared tables). By this comparing i should check equal records (equal = equal by set of defined keys (columns in these input ...
0
votes
2answers
81 views

Preventing sysquerymetrics from being created ASE 15.7

Can I prevent Sybase ASE 15.7 from creating the sysquerymetrics view for a database upon creation? And also, if the view is dropped how can it be added later?
1
vote
2answers
358 views

Perl - MySQL/MariaDB - slow with no identifiable bottleneck

I am running a Perl script (using DBI) which reads from raw files from a hard disk, and updates MySQL database (which is on a separate SSD). My performance is rather slow (1000 files processed in ...
7
votes
4answers
641 views

At What Point Should I Split or Partition a Very Large but Simple Table

Our site has some large but simple (INT, INT, DATE) tables for stats. Each table has up to 300,000,000 rows, and gets bigger every day. The hosting provider has suggested that we split or partition ...
1
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2answers
142 views

Unexpectively slow data loading into Oracle

Big amount (4.000.000+) of files (1-4Mb each) are loading into Oracle 10g for about several days. Table is allocated in big tablespace, which was created on special volume (labeled BIG_VOL) over ...
2
votes
1answer
57 views

Resource cost of a blocked query

I'm currently reviewing a case where an SSRS server is experiencing frequent blocking and deadlocking. The reports are not business-critical, and they are frequently killed to alleviate the blocking. ...
4
votes
2answers
1k views

Join on dm_db_index_physical_stats very slow

I'm running a small query below in a MS Dynamics AX 2012 database and it runs more than 5 minutes which I had to cancel and it is showing PAGEIOLATCH_SH wait type. The database data file is 560GB and ...
0
votes
1answer
152 views

How can I measure the number of IOPs for a certain query

I need to estimate the max IOPs for a certain MySQL DB (one that does not exist yet). The OS is Linux and the DB is MySQL 5.1.x (though I don't think the DB brand is important for the asked topic) ...
2
votes
0answers
51 views

Can CTE sub-statements be prevented from executing at all?

Through this strategy, time consumed by queries for my application have dropped to extreme lows; however, some queries consume more milliseconds than necessary. The reason why is that upon ...
1
vote
1answer
113 views

optimize design for a table with 50 columns [closed]

I have a table with 50 column and one of my friend has told me to split the table in 4 different table to save 12 column in each table. He proposed a design to have Master table and refer the PK of ...
1
vote
2answers
99 views

How to tune the below query

I am currently working on below table structure to pull the data/ generate any one time report. Let us consider the table name to be ABC. ID Field Value 1 Name Nagarjuna 1 Gender Male 1 ...
2
votes
1answer
132 views

Prepared statement overhead

I am using libpqxx to communicate with a PostgreSQL 9.3 server. For multiple table inserts, if they are split into individual prepared statements, they cost approximately 2ms each. If they are all ...
3
votes
1answer
49 views

Best Design for this “Sweepstakes” Project?

Hello there fellow developers, Merry Christmas first aff all, and i hope you will have a happy new year soon. :) I was having more or less a problem with an idea that came to my mind. I am currently ...
0
votes
0answers
161 views

Oracle - Slow queries without prepending schema name or providing hint

I am logged in as the schema owner in Oracle 11gR2 on Linux. I have 55 million rows in table. select max(col) from table; - takes 300 seconds (index full scan) select max(col) from schema.table; - ...
4
votes
5answers
4k views

Is it advantageous to scale out using multiple SQL Server instances on the same server?

For a use-case of 9 databases spread across 3 time zones, is it advantagous to spread the databases onto multiple SQL Server instances on the same server? What will I gain and what will I lose? ...
0
votes
0answers
66 views

Data warehousing: data transfer process too slow with larger batches

I have two primary instances of SQL Server, one for OLTP and one for reporting. The data warehouse for reporting is basically a Type 2 SCD: every table has DWDateStart and DWDateEnd columns and the ...
0
votes
0answers
71 views

What minimum RAM should the server have for a Django application with Postgresql server?

I have a Django application. The database is Postgresql with 8GB size. We are also using Nginx with gunicorn. Will a 4GB server be enough for good performance ( like on Digital Ocean) ? I was under ...
2
votes
4answers
471 views

Help understanding SQL Server 2005 execution plan

One of my stored procedure has long execution time (average around 4 to 7 minutes). Now I trying to tweak it an make it run faster. I am looking at execution plan and two things I see that using ...
7
votes
1answer
101 views

Is there a performance hit by breaking out tables into different schemas in SQL Server?

Is there any kind of performance hit when querying by placing tables in different schemas in SQL Server. For instance if I had 2 tables, Table1 and Table2, and put Table1 into the test schema and ...
0
votes
1answer
83 views

Large long-running reporting queries are causing very slow new mysql connections

Usually, mysql's connecton time is in the 0.001 second range. However, when I run a large reporting query (that spans multiple tables with aggregates), I get tons of warnings saying that new mysql ...
1
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0answers
17 views

Can MySQL Index Merge an Composite index with a single column index?

I am tuning a query and currently have an index as following : Index 1 : (col1, col2) An example query would be : SELECT * FROM t1 WHERE col1 = '1' AND col3 = '2'; I have created an index on ...