This question appeared couple of times on irc, so I figured I can do a blogpost about it.
Continue reading How to make sure there is always at least one “sub" record?
Tag: postgresql
explain.depesz.com, paste.depesz.com – TOR announcement and some updates
I assume that you're familiar with explain.depesz.com and paste.depesz.com services.
From today they are also available as services in TOR, using respectively: explain4pg4j5wbw.onion and paste4sql64vzyry.onion (of course you need to have TOR Browser or some other way to browse darknet).
Why I did that? Well, I believe that TOR is one of the greatest inventions ever, and I'd like to do something so that it will be less associated with drugs, porn, or other illegal activities. Don't realistically think that there will be many people using TOR to access my Pg-related services, but it is a thing that I could have done, so I did it.
While working on it, I also updated pgFormatter code under paste-site to newest version.
Continue reading explain.depesz.com, paste.depesz.com – TOR announcement and some updates
New change on explain.depesz.com
Some (long) time ago, someone on irc suggested that I add option to keep track of optimizations of queries.
Sorry, I forgot your name, and the mails disappeared in some crash.
Anyway – right now, when you are on some plan page, you can press “Add optimization" button, and you will be redirected to index page, but when you will add plan there, it will be understood to be plan from optimization of the query. Like this one.
You can have any number of optimizations per plan, and when viewing plan that has optimizations, or is an optimization of earlier plan – you will see this above plan table.
Whether you'll use it – it's up to you. Someone wanted it, and it looked like sensible thing to add, so there it is 🙂
Waiting for PostgreSQL 10 – Implement multivariate n-distinct coefficients
I missed it completely, but on 24th of March 2017, Alvaro Herrera committed patch:
Implement multivariate n-distinct coefficients
Add support for explicitly declared statistic objects (CREATE
STATISTICS), allowing collection of statistics on more complex
combinations that individual table columns. Companion commands DROP
STATISTICS and ALTER STATISTICS ... OWNER TO / SET SCHEMA / RENAME are
added too. All this DDL has been designed so that more statistic types
can be added later on, such as multivariate most-common-values and
multivariate histograms between columns of a single table, leaving room
for permitting columns on multiple tables, too, as well as expressions.
This commit only adds support for collection of n-distinct coefficient
on user-specified sets of columns in a single table. This is useful to
estimate number of distinct groups in GROUP BY and DISTINCT clauses;
estimation errors there can cause over-allocation of memory in hashed
aggregates, for instance, so it's a worthwhile problem to solve. A new
special pseudo-type pg_ndistinct is used.
(num-distinct estimation was deemed sufficiently useful by itself that
this is worthwhile even if no further statistic types are added
immediately; so much so that another version of essentially the same
functionality was submitted by Kyotaro Horiguchi:
https://postgr.es/m/.173334..horiguchi.kyotaro@lab.ntt.co.jp
though this commit does not use that code.)
Author: Tomas Vondra. Some code rework by Álvaro.
Ideriha Takeshi
Discussion: https://postgr.es/m/.4080608@fuzzy.cz
https://postgr.es/m/.ixlaueanxegqd5gr@alvherre.pgsqlAfterwards, there were couple more commits related to it:
- On 5th of April 2017, patch committed by Simon Riggs
- On 17th of April 2017, patch committed by Alvaro Herrera
- On 12nd of May 2017, patch committed by Alvaro Herrera
Continue reading Waiting for PostgreSQL 10 – Implement multivariate n-distinct coefficients
Waiting for PostgreSQL 10 – Support SCRAM-SHA-256 authentication (RFC 5802 and 7677).
On 7th of March 2017, Heikki Linnakangas committed patch:
Support SCRAM-SHA-256 authentication (RFC 5802 and 7677). This introduces a new generic SASL authentication method, similar to the GSS and SSPI methods. The server first tells the client which SASL authentication mechanism to use, and then the mechanism-specific SASL messages are exchanged in AuthenticationSASLcontinue and PasswordMessage messages. Only SCRAM-SHA-256 is supported at the moment, but this allows adding more SASL mechanisms in the future, without changing the overall protocol. Support for channel binding, aka SCRAM-SHA-256-PLUS is left for later. The SASLPrep algorithm, for pre-processing the password, is not yet implemented. That could cause trouble, if you use a password with non-ASCII characters, and a client library that does implement SASLprep. That will hopefully be added later. Authorization identities, as specified in the SCRAM-SHA-256 specification, are ignored. SET SESSION AUTHORIZATION provides more or less the same functionality, anyway. If a user doesn't exist, perform a "mock" authentication, by constructing an authentic-looking challenge on the fly. The challenge is derived from a new system-wide random value, "mock authentication nonce", which is created at initdb, and stored in the control file. We go through these motions, in order to not give away the information on whether the user exists, to unauthenticated users. Bumps PG_CONTROL_VERSION, because of the new field in control file. Patch by Michael Paquier and Heikki Linnakangas, reviewed at different stages by Robert Haas, Stephen Frost, David Steele, Aleksander Alekseev, and many others. Discussion: https://www.postgresql.org/message-id/CAB7nPqRbR3GmFYdedCAhzukfKrgBLTLtMvENOmPrVWREsZkF8g%40mail.gmail.com Discussion: https://www.postgresql.org/message-id/CAB7nPqSMXU35g%3DW9X74HVeQp0uvgJxvYOuA4A-A3M%2B0wfEBv-w%40mail.gmail.com Discussion: https://www.postgresql.org/message-id/.6080106@iki.fi
Waiting for PostgreSQL 10 – Identity columns
On 6th of April 2017, Peter Eisentraut committed patch:
Identity columns This is the SQL standard-conforming variant of PostgreSQL's serial columns. It fixes a few usability issues that serial columns have: - CREATE TABLE / LIKE copies default but refers to same sequence - cannot add/drop serialness with ALTER TABLE - dropping default does not drop sequence - need to grant separate privileges to sequence - other slight weirdnesses because serial is some kind of special macro
Continue reading Waiting for PostgreSQL 10 – Identity columns
Waiting for PostgreSQL 10 – Full Text Search support for json and jsonb
On 31st of March 2017, Andrew Dunstan committed patch:
Full Text Search support for json and jsonb The new functions are ts_headline() and to_tsvector. Dmitry Dolgov, edited and documented by me.
Continue reading Waiting for PostgreSQL 10 – Full Text Search support for json and jsonb
Waiting for PostgreSQL 10 – Support \if … \elif … \else … \endif in psql scripting.
On 30th of March 2017, Tom Lane committed patch:
Support \if ... \elif ... \else ... \endif in psql scripting. This patch adds nestable conditional blocks to psql. The control structure feature per se is complete, but the boolean expressions understood by \if and \elif are pretty primitive; basically, after variable substitution and backtick expansion, the result has to be "true" or "false" or one of the other standard spellings of a boolean value. But that's enough for many purposes, since you can always do the heavy lifting on the server side; and we can extend it later. Along the way, pay down some of the technical debt that had built up around psql/command.c: * Refactor exec_command() into a function per command, instead of being a 1500-line monstrosity. This makes the file noticeably longer because of repetitive function header/trailer overhead, but it seems much more readable. * Teach psql_get_variable() and psqlscanslash.l to suppress variable substitution and backtick expansion on the basis of the conditional stack state, thereby allowing removal of the OT_NO_EVAL kluge. * Fix the no-doubt-once-expedient hack of sometimes silently substituting mainloop.c's previous_buf for query_buf when calling HandleSlashCmds. (It's a bit remarkable that commands like \r worked at all with that.) Recall of a previous query is now done explicitly in the slash commands where that should happen. Corey Huinker, reviewed by Fabien Coelho, further hacking by me Discussion: https://postgr.es/m/CADkLM=c94OSRTnat=LX0ivNq4pxDNeoomFfYvBKM5N_xfmLtAA@mail.gmail.com
Continue reading Waiting for PostgreSQL 10 – Support \if … \elif … \else … \endif in psql scripting.
Waiting for PostgreSQL 10 – Logical replication support for initial data copy
On 23rd of March 2017, Peter Eisentraut committed patch:
Logical replication support for initial data copy Add functionality for a new subscription to copy the initial data in the tables and then sync with the ongoing apply process. For the copying, add a new internal COPY option to have the COPY source data provided by a callback function. The initial data copy works on the subscriber by receiving COPY data from the publisher and then providing it locally into a COPY that writes to the destination table. A WAL receiver can now execute full SQL commands. This is used here to obtain information about tables and publications. Several new options were added to CREATE and ALTER SUBSCRIPTION to control whether and when initial table syncing happens. Change pg_dump option --no-create-subscription-slots to --no-subscription-connect and use the new CREATE SUBSCRIPTION ... NOCONNECT option for that. Author: Petr Jelinek
Continue reading Waiting for PostgreSQL 10 – Logical replication support for initial data copy
Waiting for PostgreSQL 10 – hash indexing vs. WAL
For a long time hash indexed were not crash safe, and couldn't be used on replication slave, because they skipped WAL. Now, thanks to these two commits, it has changed:
On 14th of March 2017, Robert Haas committed patch:
hash: Add write-ahead logging support. The warning about hash indexes not being write-ahead logged and their use being discouraged has been removed. "snapshot too old" is now supported for tables with hash indexes. Most importantly, barring bugs, hash indexes will now be crash-safe and usable on standbys. This commit doesn't yet add WAL consistency checking for hash indexes, as we now have for other index types; a separate patch has been submitted to cure that lack. Amit Kapila, reviewed and slightly modified by me. The larger patch series of which this is a part has been reviewed and tested by Álvaro Herrera, Ashutosh Sharma, Mark Kirkwood, Jeff Janes, and Jesper Pedersen. Discussion: http://postgr.es/m/CAA4eK1JOBX=YU33631Qh-XivYXtPSALh514+jR8XeD7v+K3r_Q@mail.gmail.com
and then, ~ 13 hours later, Robert committed also:
hash: Support WAL consistency checking. Kuntal Ghosh, reviewed by Amit Kapila and Ashutosh Sharma, with a few tweaks by me. Discussion: http://postgr.es/m/CAGz5QCJLERUn_zoO0eDv6_Y_d0o4tNTMPeR7ivTLBg4rUrJdwg@mail.gmail.com
Continue reading Waiting for PostgreSQL 10 – hash indexing vs. WAL