A bit ago I wrote a blog post that was supposed to show how to keep number of rows in table to N per some category.
Unfortunately, I overlooked a problem related to concurrency.
Continue reading How to limit rows to at most N per category – fix
Tag: postgresql
Fixes on why-upgrade.depesz.com
In case you're not familiar with this site, why-upgrade.depesz.com shows you aggregated changelog between any two releases, with optionally searching for some keywords.
Yesterday azeem on irc pointed me towards a problem on why-upgrade.depesz.com. Specifically, when displaying changes from 9.5.24 to 13.1 site showed 30 security fixes. But in reality there should be only 10.
How to install and configure PostgreSQL Debian/Ubuntu – for developer use – part 2
In previous post I showed how I'd install PostgreSQL for developer.
But that's not all. Now we need to add some configuration. What, how, where?
Continue reading How to install and configure PostgreSQL Debian/Ubuntu – for developer use – part 2
How to install and configure PostgreSQL Debian/Ubuntu – for developer use – part 1
Recently I spent some time thinking about what can be improved when it comes to helping new users start using PostgreSQL.
One thing that almost immediately jumped to my mind is – how to install PostgreSQL? The task is theoretically simple. But there are always some caveats – which packages to use, what to configure in the beginning, where to find config files and logs.
With that in mind I decided to write a howto based on my ideas on what is right. These do not necessarily mean that these are the best for everybody, but I think this is a good start for anyone wanting to start their adventure with PostgreSQL.
Final note of warning – this post is for installing and setting PostgreSQL on developer workstation. As in: server where user can do anything, and we don't really care about security. Please do not configure production servers using this howto.
Continue reading How to install and configure PostgreSQL Debian/Ubuntu – for developer use – part 1
Waiting for PostgreSQL 14 – Multirange datatypes
On 20th of December 2020, Alexander Korotkov committed patch:
Multirange datatypes Multiranges are basically sorted arrays of non-overlapping ranges with set-theoretic operations defined over them. Since v14, each range type automatically gets a corresponding multirange datatype. There are both manual and automatic mechanisms for naming multirange types. Once can specify multirange type name using multirange_type_name attribute in CREATE TYPE. Otherwise, a multirange type name is generated automatically. If the range type name contains "range" then we change that to "multirange". Otherwise, we add "_multirange" to the end. Implementation of multiranges comes with a space-efficient internal representation format, which evades extra paddings and duplicated storage of oids. Altogether this format allows fetching a particular range by its index in O(n). Statistic gathering and selectivity estimation are implemented for multiranges. For this purpose, stored multirange is approximated as union range without gaps. This field will likely need improvements in the future. Catversion is bumped. Discussion: https://postgr.es/m/CALNJ-vSUpQ_Y%3DjXvTxt1VYFztaBSsWVXeF1y6gTYQ4bOiWDLgQ%40mail.gmail.com Discussion: https://postgr.es/m/a0b8026459d1e6167933be2104a6174e7d40d0ab.camel%40j-davis.com#fe7218c83b08068bfffb0c5293eceda0 Author: Paul Jungwirth, revised by me Reviewed-by: David Fetter, Corey Huinker, Jeff Davis, Pavel Stehule Reviewed-by: Alvaro Herrera, Tom Lane, Isaac Morland, David G. Johnston Reviewed-by: Zhihong Yu, Alexander Korotkov
Continue reading Waiting for PostgreSQL 14 – Multirange datatypes
Waiting for PostgreSQL 14 – pg_stat_statements: Track time at which all statistics were last reset.
On 18th of December 2020, Fujii Masao committed patch:
pg_stat_statements: Track time at which all statistics were last reset. This commit adds "stats_reset" column into the pg_stat_statements_info view. This column indicates the time at which all statistics in the pg_stat_statements view were last reset. Per discussion, this commit also changes pg_stat_statements_info code so that "dealloc" column is reset at the same time as "stats_reset" is reset, i.e., whenever all pg_stat_statements entries are removed, for the sake of consistency. Previously "dealloc" was reset only when pg_stat_statements_reset(0, 0, 0) is called and was not reset when pg_stat_statements_reset() with non-zero value argument discards all entries. This was confusing. Author: Naoki Nakamichi, Yuki Seino Reviewed-by: Yuki Seino, Kyotaro Horiguchi, Li Japin, Fujii Masao Discussion: https://postgr.es/m/c102cf3180d0ee73c1c5a0f7f8558322@oss.nttdata.com
Waiting for PostgreSQL 14 – Allow subscripting of hstore values.
On 11st of December 2020, Tom Lane committed patch:
Allow subscripting of hstore values. This is basically a finger exercise to prove that it's possible for an extension module to add subscripting ability. Subscripted fetch from an hstore is not different from the existing "hstore -> text" operator. Subscripted update does seem to be a little easier to use than the traditional update method using hstore concatenation, but it's not a fundamentally new ability. However, there may be some value in the code as sample code, since it shows what's basically the minimum-complexity way to implement subscripting when one needn't consider nested container objects. Discussion: https://postgr.es/m/3724341.1607551174@sss.pgh.pa.us
Continue reading Waiting for PostgreSQL 14 – Allow subscripting of hstore values.
How to limit rows to at most N per category
The question was asked relatively recently on irc. And it proved to be non-trivial.
Surely, if you want to have one row per category (one address per user), it's trivial – add user_id column to addresses, make it unique, and we're done. But what if we want to allow five addresses? Or five thousands?
Let's see.
Continue reading How to limit rows to at most N per category
Waiting for PostgreSQL 14 – Provide the OR REPLACE option for CREATE TRIGGER.
On 14th of November 2020, Tom Lane committed patch:
Provide the OR REPLACE option for CREATE TRIGGER. This is mostly straightforward. However, we disallow replacing constraint triggers or changing the is-constraint property; perhaps that can be added later, but the complexity versus benefit tradeoff doesn't look very good. Also, no special thought is taken here for whether replacing an existing trigger should result in changes to queued-but-not-fired trigger actions. We just document that if you're surprised by the results, too bad, don't do that. (Note that any such pending trigger activity would have to be within the current session.) Takamichi Osumi, reviewed at various times by Surafel Temesgen, Peter Smith, and myself Discussion: https://postgr.es/m/0DDF369B45A1B44B8A687ED43F06557C010BC362@G01JPEXMBYT03
Continue reading Waiting for PostgreSQL 14 – Provide the OR REPLACE option for CREATE TRIGGER.
Waiting for PostgreSQL 14 – Support negative indexes in split_part().
On 13rd of November 2020, Tom Lane committed patch:
Support negative indexes in split_part(). This provides a handy way to get, say, the last field of the string. Use of a negative index in this way has precedent in the nearby left() and right() functions. The implementation scans the string twice when N < -1, but it seems likely that N = -1 will be the huge majority of actual use cases, so I'm not really excited about adding complexity to avoid that. Nikhil Benesch, reviewed by Jacob Champion; cosmetic tweakage by me Discussion: https://postgr.es/m/cbb7f861-6162-3a51-9823-97bc3aa0b638@gmail.com
Continue reading Waiting for PostgreSQL 14 – Support negative indexes in split_part().