PostgreSQL is an enterprise class, open-source, object-relational database management system (ORDBMS) available for all major platforms including Linux, UNIX, Windows and OS X. Please mention your exact PostgreSQL version when asking questions.

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23
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3answers
23k views

Find highest level of a hierarchical field: with vs without CTEs

note: this question has been updated to reflect that we are currently using MySQL, having done so, I would like to see a how much easier it would be if we switched to a CTE-supporting database. I ...
19
votes
2answers
4k views

Is a composite index also good for queries on the first field?

Let's say I have a table with fields A and B. I make regular queries on A+B, so I created a composite index on (A,B). Would queries on only A also be fully optimized by the composite index? ...
17
votes
3answers
6k views

Is the CPU performance relevant for a database server?

This is a purely theoretical question. Let's say I have an application deployed on multiple servers. A load balancer, Multiple/scalable applications servers A (single) database server (for the ...
3
votes
2answers
3k views

Configuring PostgreSQL for read performance

Our system write a lots of data (kind of Big Data system). The write performance is good enough for our needs but the read performance is really too slow. The primary key (constraint) structure is ...
25
votes
5answers
7k views

Working of indexes in PostgreSQL

I have a couple of questions regarding working of indexes in PostgreSQL. I have a Friends table with the following index: Friends ( user_id1 ,user_id2) user_id1 and user_id2 are foreign keys to ...
13
votes
3answers
8k views

Measure the size of a PostgreSQL table row

I have a PostgreSQL table. select * is very slow whereas select id is nice and quick. I think it may be that the size of the row is very large and it's taking a while to transport, or it may be some ...
19
votes
4answers
16k 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 ...
11
votes
3answers
981 views

Can spatial index help a “range - order by - limit” query

Asking this question, specifically for Postgres, as it has good supoort for R-tree/spatial indexes. We have the following table with a tree structure (Nested Set model) of words and their ...
5
votes
3answers
3k views

Postgres Write Performance on Intel S3700 SSD

I'm not seeing the Postgres write performance increases I thought I would with a single SSD vs a hardware RAID 10 array of (16) 15k RPM SAS drives. I have a Dell R820 with a PERC H700 hardware RAID ...
8
votes
2answers
6k views

Optimizing bulk update performance in PostgreSQL

Using PG 9.1 on Ubuntu 12.04. It currently takes up to 24h for us to run a large set of UPDATE statements on a database, which are of the form: UPDATE table SET field1 = constant1, field2 = ...
7
votes
3answers
32k views

How do I insert a row which contains a foreign key?

Using PostgreSQL v9.1. I have the following tables: CREATE TABLE foo ( id BIGSERIAL NOT NULL UNIQUE PRIMARY KEY, type VARCHAR(60) NOT NULL UNIQUE ); CREATE TABLE bar ( id BIGSERIAL ...
19
votes
4answers
7k views

PostgreSQL Stored Procedure Performance

Coming from a MySQL background, where stored procedure performance (older article) and usability are questionable, I am evaluating PostgreSQL for a new product for my company. One of the things I ...
22
votes
3answers
14k views

PostgreSQL multi-column unique constraint and NULL values

I have a table like the following: create table my_table ( id int8 not null, id_A int8 not null, id_B int8 not null, id_C int8 null, constraint pk_my_table primary key (id), ...
20
votes
6answers
14k views

How do I efficiently get “the most recent corresponding row”?

I have a query pattern that must be very common, but I don't know how to write an efficient query for it. I want to look up the rows of a table that correspond to "the most recent date not after" the ...
6
votes
3answers
3k views

Should I add an arbitrary length limit to VARCHAR columns?

According to PostgreSQL's docs, there's no performance difference between VARCHAR, VARCHAR(n) and TEXT. Should I add an arbitrary length limit to a name or address column?
6
votes
3answers
558 views

Issue with composite type in an UPSERT function

I have a function in PostgreSQL 9.1 called fun_test. It has a composite type as input parameter and I keep getting a casting error when I call it. CREATE OR REPLACE FUNCTION netcen.fun_test(myobj ...
7
votes
1answer
2k views

SQL injection in Postgres functions vs prepared queries

In Postgres, are prepared queries and user defined functions equivalent as a mechanism for guarding against SQL injection? Are there particular advantages in one approach over the other?
10
votes
2answers
477 views

Postgres query plan of a UDF invocation written in pgpsql

It's possible when using the pgadmin or plsql to get a hold of a query plan for a sql statement executed via a UDF (using EXPLAIN). So, how do I get a hold of the query plan for a particular ...
9
votes
4answers
10k views

Aggressive Autovacuum on PostgreSQL

I'm trying to get PostgreSQL to aggressively auto vacuum my database. I've currently configured auto vacuum as follows: autovacuum_vacuum_cost_delay = 0 #Turn off cost based vacuum ...
56
votes
5answers
5k views

Do stored procedures prevent SQL injection?

Is it true that stored procedures prevent SQL injection attacks against PostgreSQL databases? I did a little research and found out that SQL Server, Oracle and MySQL are not safe against SQL injection ...
9
votes
3answers
2k views

How is LIKE implemented?

Can anyone explain how the LIKE operator is implemented in current database systems (e.g. MySQL or Postgres)? or point me to some references that explain it? The naive approach would be to inspect ...
6
votes
1answer
6k views

How to use aes-encryption in PostgreSQL?

I tried aes-encryption by using following statement: SELECT encrypt('test', 'key', 'aes'); which worked, but I am not able to decrypt the value. I inserted it in a field of datatype bytea but I'm ...
7
votes
1answer
1k views

Algorithm for finding the longest prefix

I have two tables. First one is a table with prefixes code name price 343 ek1 10 3435 nt 4 3432 ek2 2 Second is call records with phone numbers number time 834353212 10 ...
6
votes
1answer
3k views

How to determine the sweet spot between pool size and database connections in PostgreSQL

We are having trouble handling the traffic during peak hours to our database server. We're looking into improving the hardware (see this question about that side of things) but we also want to work on ...
9
votes
2answers
2k views

Best way to populate a new column in a large table?

We have a 2.2 GB table in Postgres with 7,801,611 rows in it. We are adding a uuid/guid column to it and I am wondering what the best way to populate that column is (as we want to add a NOTNULL to ...
7
votes
1answer
2k views

PostgreSQL Failover - What tools should I use?

Here is the scenario: There are two machines running CentOS 6.2 - machine0 and machine1 Both have PostgreSQL 9.1 installed. One of them should be active, as a master system and through asynchronous ...
5
votes
1answer
1k views

Get WAL files from AWS RDS PostgreSQL instance

We have a Postgres RDS instance on Amazon Web Services. We have automatic backups enabled, and we take snapshots on a daily basis. We would like to generate a local 'up-to-date' backup of the RDS ...
14
votes
3answers
8k views

Are regular VACUUM ANALYZE stil recommended under 9.1?

I'm using PostgreSQL 9.1 on Ubuntu. Are scheduled VACUUM ANALYZE still recommended, or is autovacuum enough to take care of all needs? If the answer is "it depends", then: I have a largish database ...
11
votes
4answers
30k views

How to insert (file) data into a PostgreSQL bytea column

This question is not about bytea v. oid v. blobs v. large objects, etc. I have a table containing a primary key integer field and a bytea field. I'd like to enter data into the bytea field. This ...
6
votes
2answers
2k views

Multicolumn index and performance

I have a table with a multicolumn index, and I have doubts about the proper sorting of the indexes to get the maximum performance on the queries. The scenario: PostgreSQL 8.4, table with about 1MM ...
5
votes
2answers
6k views

How to turn json array into postgres array?

I have a field user that holds a json document that roughly looks like that: { name: 'foo', tags: ['foo', 'bar'] } What I would like to do is to turn that tags array into a concatenated ...
9
votes
1answer
2k views

How to preserve the original order of elements in an unnested array?

Given the string: 'I think that PostgreSQL is nifty' I would like to operate on the individual words found within that string. Essentially, I have a separate from which I can get word details ...
4
votes
1answer
1k views

PostgreSQL 9.2: vacuum returning disk space to operating system

Vacuum usually does not return disk space to operating system, except some special cases. From the docs: The standard form of VACUUM removes dead row versions in tables and indexes and marks the ...
4
votes
2answers
2k views

Index max row size error

Is there a upper bound for an array column? I am getting this error when inserting into the array field - PG::Error: ERROR: index row size 3480 exceeds maximum 2712 for index "ix_data" Here's my ...
4
votes
2answers
922 views

PostgreSQL unexplained table bloat

I have a table in a Postgres 8.2.15 database. The table bloated to almost 25GB but after running vacuum full and cluster the table size was dramatically smaller, well under 1GB. A few weeks later ...
3
votes
1answer
969 views

How to create an index on an integer json property in postgres

I can't figure out for the life of me how to create an index on a property of my json column which is an integer. I tried it this way (and also dozens of others) CREATE INDEX user_reputation_idx ON ...
2
votes
6answers
76 views

Need separate columns that calculate percentage

I have the following table: NAME Alex Bob Bob Tim Alex Roger I need to produce the following: Name Count Percentage Alex 2 33% Bob 2 33% Roger 1 16.6% Tim 1 ...
8
votes
1answer
2k views

PostgreSQL EXCLUDE USING error: Data type integer has no default operator class

In PostgreSQL 9.2.3 I am trying to create this simplified table: CREATE TABLE test ( user_id INTEGER, startend TSTZRANGE, EXCLUDE USING gist (user_id WITH =, startend WITH &&) ); ...
4
votes
2answers
1k views

Inner join using an array column

Having trouble indexing and executing a query in O (log n) time. The query includes an INNER JOIN, an ORDER BY, and an equality operation. If I understand the laws of databases correctly, a query can ...
4
votes
2answers
715 views

Select longest continuous sequence

I am trying to construct a query in PostgreSQL 9.0 that gets the longest sequence of continuous rows for a specifc field. Consider the following table: lap_id (Serial), lap_no (int), car_type ...
19
votes
9answers
41k views

PostgreSQL is running locally but I cannot connect. Why?

Recently updated my machine from Mac OS X Lion (10.7.4) to Mountain Lion (10.8) and I think it borked my PostgreSQL installation. It was installed originally via Homebrew. I'm not a DBA, but hoping ...
21
votes
3answers
37k views

How do I list all columns for a specified table

I'm looking for a precise piece of information in a database which I have no knowledge about. It's a 3rd party product, they are slow on answering some questions, and I know the data is lying inside ...
22
votes
1answer
3k views

USING construct in JOIN clause can introduce optimization barriers in certain cases?

It was brought to my attention that the USING construct (instead of ON) in the FROM clause of SELECT queries might introduce optimization barriers in certain cases. I mean this key word: SELECT * ...
13
votes
1answer
3k views

How can I benchmark a PostgreSQL query?

I want to benchmark a query containing an user-defined function I have written for PostgreSQL. Are there any standard ways to run such a benchmark? I know that timing can be turned on with \timing ...
9
votes
3answers
10k views

Optimizing queries on a range of timestamps (two columns)

I use postgresql-9.1 with ubuntu 12.04. I need to select records inside a range of time: my table time_limits has two timestamp fields and one property integer. Indeed there are other info columns ...
15
votes
1answer
16k views

Optimal way to ignore duplicate inserts?

Background This problem relates to ignoring duplicate inserts using PostgreSQL 9.2 or greater. The reason I ask is because of this code: -- Ignores duplicates. INSERT INTO db_table ...
15
votes
2answers
12k views

Force drop db while others may be connected in postgresql

I need to remove a database in postgresql DB. How can I do it even if there are active connections? I need a sort of -force flag, that will drop all connections and then the DB. How can I implement ...
11
votes
1answer
1k views

Why does NOT IN with a set containing NULL always return FALSE/NULL?

I had a query (for Postgres and Informix) with a NOT IN clause containing a subquery that in some cases returned NULL values, causing that clause (and the entire query) to fail to return anything. ...
1
vote
2answers
1k views

Moving a Postgres database from standalone local DB to Amazon RDS

I have a working Ruby on Rails 4 app running locally on my Mac. I'm running Postgres locally. I want to move the database (and only the database, not the whole app) to Amazon RDS Postgres. What is ...
4
votes
1answer
713 views

What AWS instance to choose for write-heavy PostgreSQL database server

We are now having problems trouble to tackle the intensive traffic to our servers during peak hours; see this related question on tuning the DB. At the moment we are using a smaller cloud service for ...