2
votes
1answer
113 views

Why is CTE open to lost updates?

I don't understand what Craig Ringer meant when he commented: This solution is subject to lost updates if the inserting transaction rolls back; there's no check to enforce that the UPDATE affected ...
1
vote
1answer
73 views

Improve performance on concurrent UPDATEs for a timestamp column in Postgres

I am using a timestamp column called updated_at for cache invalidation. More information on this particular technique here. The queries all have the same format UPDATE "managers" SET "updated_at" = ...
0
votes
1answer
54 views

PostgreSQL - If I run multiple queries concurrently, under what circumstances would I see a speedup? Under what circumstances would I see a slowdown?

I approach you all humbly as one who is NOT a DBA, and I'm sure that my question is fraught with conceptual shortcomings and "it depends on" land mines. I'm also pretty sure that all of you who ...
3
votes
1answer
383 views

Postgres Update, limit 1

I have a postgres database which contains details on clusters of servers, such as server status (active, standby, etc). Active servers at any time may need to fail over to a standby, and I don't care ...
2
votes
2answers
81 views

Tuning Postgres for Single connection use? Or is postgres wrong tool?

Any rules of thumb for work_mem, maintenance_work_mem, shared_buffer, etc. for a database that DOESN'T anticipate concurrent connections and that is doing lots of aggregate functions? I'm a social ...
0
votes
1answer
213 views

How to create fault tolerant databases? [closed]

I have a local application running on a LAN. Sometimes a database gets shutdown. In such a scenario how can I keep the application working? Can I have two concurrent databases so that one picks up the ...
5
votes
2answers
133 views

Inconsistency in repeatable read

http://www.postgresql.org/docs/9.2/static/transaction-iso.html The Repeatable Read mode provides a rigorous guarantee that each transaction sees a completely stable view of the database. However, ...
3
votes
1answer
1k views

PostgreSQL concurrent increment of counter

I need to maintain a statistical table for a project, composed by a list of items and their usage (Think about something like a website in which you would like to count pageviews). Each time an item ...
5
votes
1answer
882 views

How to improve performance on PostgreSQL when using multiple concurrent processes?

Seeing query performance which is not satisfactory on our Python application, which runs several processes that use SQLAlchemy core to access a PostgreSQL 9.2 database. We may have around 100 - 200 ...
12
votes
4answers
3k views

Locking issue with concurrent DELETE / INSERT in PostgreSQL

This is pretty simple, but I'm baffled by what PG does (v9.0). We start with a simple table: CREATE TABLE test (id INT PRIMARY KEY); and a few rows: INSERT INTO TEST VALUES (1); INSERT INTO TEST ...
4
votes
1answer
506 views

How large should my pool size be? And should I use pgbouncer?

I have a Rails application with 4 Unicorn workers. How do I determine what postgresql database pool size I should use? And if I have 6 applications connecting to this postgres database, would that be ...
4
votes
1answer
1k views

Concurrency with Select-conditional Insert/Update/Delete - PostgreSQL

I have an intervals table which stores a start date and an end date for variables variable_id (four columns : id, start, end, variable_id). Clients compute new intervals for one variable and store ...