Postgres 9.5: three little things

By Greg Sabino Mullane

January 28, 2016

The recent release of Postgres 9.5 has many people excited about the big new features such as UPSERT (docs) and row-level security (docs). Today I would like to celebrate three of the smaller features that I love about this release.

Before jumping into my list, I’d like to thank everyone who contributes to Postgres. I did some quick analysis and found that 85 people, from Adrien to Zeus, have helped version 9.5 of Postgres, at least according to the git logs. Of course, that number is actually higher, as it doesn’t take into account people helping out on the #postgresql channel, running buildfarm animals, doing packaging work, keeping the infrastructure running, etc. Thanks to you all!

Feature: REINDEX VERBOSE

The first feature is one I’ve been wishing for a long time—​a verbose form of the REINDEX command. Thanks to Sawada Masahiko for adding this. Similar to VACUUM, REINDEX gets kicked off and then gives no progress or information until it finishes. While VACUUM has long had the VERBOSE option to get around this, REINDEX gives you no clue to which index it was working on, or how much work each index took to rebuild. Here is a normal reindex, along with another 9.5 feature, the ability to reindex an entire schema:

greg=# reindex schema public; ## What seems like five long minutes later... REINDEX

The new syntax uses parenthesis to support VERBOSE and any other future options. If you are familiar with EXPLAIN’s newer options, you may see a similarity. More on the syntax in a bit. Here is the much improved version in action:

greg=# reindex (verbose) schema public; INFO: index "foobar_pkey" was reindexed DETAIL: CPU 11.00s/0.05u sec elapsed 19.38 sec. INFO: index "foobar_location" was reindexed DETAIL: CPU 5.21s/0.05u sec elapsed 18.27 sec. INFO: index "location_position" was reindexed DETAIL: CPU 9.10s/0.05u sec elapsed 19.70 sec. INFO: table "public.foobar" was reindexed INFO: index "foobaz_pkey" was reindexed DETAIL: CPU 7.04s/0.05u sec elapsed 19.61 sec. INFO: index "shoe_size" was reindexed DETAIL: CPU 12.26s/0.05u sec elapsed 19.33 sec. INFO: table "public.foobaz" was reindexed REINDEX

Why not REINDEX VERBOSE TABLE foobar? Or even REINDEX TABLE foobar WITH VERBOSE? There was a good discussion of this on pgsql-hackers when this feature was being developed, but the short answer is that parenthesis are the correct way to do things moving forward. Robert Haas summed it up well:

The unparenthesized VACUUM syntax was added back before we realized that that kind of syntax is a terrible idea. It requires every option to be a keyword, and those keywords have to be in a fixed order. I believe the intention is to keep the old VACUUM syntax around for backward-compatibility, but not to extend it. Same for EXPLAIN and COPY.

The psql help option should show the new syntax:

greg=# \h REINDEX Command: REINDEX Description: rebuild indexes Syntax: REINDEX [ ( { VERBOSE } [, ...] ) ] { INDEX | TABLE | SCHEMA | DATABASE | SYSTEM } name

Feature: pg_ctl defaults to “fast” mode

The second feature in Postgres 9.5 I am happy about is the change in niceness of pg_ctl from “smart” mode to “fast” mode. The help of pg_ctl explains the different modes fairly well:

pg_ctl is a utility to initialize, start, stop, or control a PostgreSQL server. Usage: pg_ctl stop [-W] [-t SECS] [-D DATADIR] [-s] [-m SHUTDOWN-MODE] ... Shutdown modes are: smart quit after all clients have disconnected fast quit directly, with proper shutdown immediate quit without complete shutdown; will lead to recovery on restart

In the past, the default was “smart”. Which often means your friendly neighborhood DBA would type “pg_ctl restart -D data”, then watch the progress dots slowly marching across the screen, until they remembered that the default mode of “smart” is kind of dumb—​as long as there is one connected client, the restart will not happen. Thus, the DBA had to cancel the command, and rerun it as “pg_ctl restart -D data -m fast”. Then they would vow to remember to add the -m switch in next time. And promptly forget to the next time they did a shutdown or restart. :) Now pg_ctl has a much better default. Thanks, Bruce Momjian!

Feature: new “cluster_name” option

When you run a lot of different Postgres clusters on your server, as I tend to do, it can be hard to tell them apart as the version and port are not reported in the ps output. I sometimes have nearly a dozen different clusters running, due to testing different versions and different applications. Similar in spirit to the application_name option, the new cluster_name option solves the problem neatly by allowing a custom string to be put in to the process title. Thanks to Thomas Munro for inventing this. So instead of this:

greg 7780 1 0 Mar01 pts/0 00:00:03 /home/greg/pg/9.5/bin/postgres -D data greg 7787 7780 0 Mar01 ? 00:00:00 postgres: logger process greg 7789 7780 0 Mar01 ? 00:00:00 postgres: checkpointer process greg 7790 7780 0 Mar01 ? 00:00:09 postgres: writer process greg 7791 7780 0 Mar01 ? 00:00:06 postgres: wal writer process greg 7792 7780 0 Mar01 ? 00:00:05 postgres: autovacuum launcher process greg 7793 7780 0 Mar01 ? 00:00:11 postgres: stats collector process greg 6773 1 0 Mar01 pts/0 00:00:02 /home/greg/pg/9.5/bin/postgres -D data2 greg 6780 6773 0 Mar01 ? 00:00:00 postgres: logger process greg 6782 6773 0 Mar01 ? 00:00:00 postgres: checkpointer process greg 6783 6773 0 Mar01 ? 00:00:04 postgres: writer process greg 6784 6773 0 Mar01 ? 00:00:02 postgres: wal writer process greg 6785 6773 0 Mar01 ? 00:00:02 postgres: autovacuum launcher process greg 6786 6773 0 Mar01 ? 00:00:07 postgres: stats collector process

One can adjust the cluster_name inside each postgresql.conf (for example, to “alpha” and “bravo”), and get this:

greg 8267 1 0 Mar01 pts/0 00:00:03 /home/greg/pg/9.5/bin/postgres -D data greg 8274 8267 0 Mar01 ? 00:00:00 postgres: alpha: logger process greg 8277 8267 0 Mar01 ? 00:00:00 postgres: alpha: checkpointer process greg 8278 8267 0 Mar01 ? 00:00:09 postgres: alpha: writer process greg 8279 8267 0 Mar01 ? 00:00:06 postgres: alpha: wal writer process greg 8280 8267 0 Mar01 ? 00:00:05 postgres: alpha: autovacuum launcher process greg 8281 8267 0 Mar01 ? 00:00:11 postgres: alpha: stats collector process greg 8583 1 0 Mar01 pts/0 00:00:02 /home/greg/pg/9.5/bin/postgres -D data2 greg 8590 8583 0 Mar01 ? 00:00:00 postgres: bravo: logger process greg 8592 8583 0 Mar01 ? 00:00:00 postgres: bravo: checkpointer process greg 8591 8583 0 Mar01 ? 00:00:04 postgres: bravo: writer process greg 8593 8583 0 Mar01 ? 00:00:02 postgres: bravo: wal writer process greg 8594 8583 0 Mar01 ? 00:00:02 postgres: bravo: autovacuum launcher process greg 8595 8583 0 Mar01 ? 00:00:07 postgres: bravo: stats collector process

There are a lot of other things added in Postgres 9.5. I recommend you visit this page for a complete list, and poke around on your own. A final shout out to all the people that are continually improving the tab-completion of psql. You rock.

database postgres