On 26th of September, Peter Eisentraut committed patch which adds:
Add ALTER TYPE ... ADD/DROP/ALTER/RENAME ATTRIBUTE Like with tables, this also requires allowing the existence of composite types with zero attributes. reviewed by KaiGai Kohei
Tag: postgresql
Performance gains from using foreign keys
Foreign keys are known for couple of things, but speeding up your system is not one of them. But sometimes, having them in place lets you make queries significantly faster.
How? Let me show you example I have seen lately (well, it's simplified example based on something much more convoluted, and definitely longer):
How to group messages into chats?
My jabber server had the feature, that it logs all messages that got sent through it.
This is pretty cool, and useful. And now, i got asked to use it to create list of conversations.
What exactly is this? Whenever I send (or receive) something there is record in database with information about which local user, communication type (send/recv), correspondent, when it happened, and what is the body of message.
And based on this, we want to list messages into chats. How?
Why is my index not being used?
This question (and its variants) show quite often on #postgresql on IRC. People get sequential scans, and are worried that it's slow and bad.
So, I hope that this blogpost will shed some light on the subject why indexes are being chosen to be used, or not.
Waiting for 9.1 – concat, concat_ws, right, left, reverse
On 24th of August, Takahiro Itagaki committed patch:
Log Message: ----------- Add string functions: concat(), concat_ws(), left(), right(), and reverse(). Pavel Stehule, reviewed by me.
Continue reading Waiting for 9.1 – concat, concat_ws, right, left, reverse
How to manage changes to your database?
Every now and then somebody asks how to make diff of database schemata.
Usual background is like: we have production database, and development database, and we want to see what is different on development to be able to change production in the same way.
Personally I think that such approach is inherently flawed. Why?
OmniPITR – hot backup on slave
Well, the biggest information is that hot-backups on slave work. And they work fine. Really fine.
Some more information (with nice graph!):
Waiting for 9.1 – Recognize functional dependency on primary keys.
Yesterday (August, 7th), Tom Lane committed:
Log Message: ----------- Recognize functional dependency on primary keys. This allows a table's other columns to be referenced without listing them in GROUP BY, so long as the primary key column(s) are listed in GROUP BY. Eventually we should also allow functional dependency on a UNIQUE constraint when the columns are marked NOT NULL, but that has to wait until NOT NULL constraints are represented in pg_constraint, because we need to have pg_constraint OIDs for all the conditions needed to ensure functional dependency. Peter Eisentraut, reviewed by Alex Hunsaker and Tom Lane
Continue reading Waiting for 9.1 – Recognize functional dependency on primary keys.
Waiting for 9.1 – Reduced lock levels for ALTER TABLE
On 28th of July, Simon Riggs committed patch which:
Log Message: ----------- Reduce lock levels of CREATE TRIGGER and some ALTER TABLE, CREATE RULE actions. Avoid hard-coding lockmode used for many altering DDL commands, allowing easier future changes of lock levels. Implementation of initial analysis on DDL sub-commands, so that many lock levels are now at ShareUpdateExclusiveLock or ShareRowExclusiveLock, allowing certain DDL not to block reads/writes. First of number of planned changes in this area; additional docs required when full project complete.
Continue reading Waiting for 9.1 – Reduced lock levels for ALTER TABLE
How to make sure you will not get any help on IRC
Some guy came to #postgresql today. Described his problem, got additional question, and then … well .. I wouldn't believe if it didn't happen to me.
Continue reading How to make sure you will not get any help on IRC