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Waiting for PostgreSQL 18 – Allow parallel CREATE INDEX for GIN indexes

On 3rd of March 2025, Tomas Vondra committed patch:

Allow parallel CREATE INDEX for GIN indexes
 
Allow using parallel workers to build a GIN index, similarly to BTREE
and BRIN. For large tables this may result in significant speedup when
the build is CPU-bound.
 
The work is divided so that each worker builds index entries on a subset
of the table, determined by the regular parallel scan used to read the
data. Each worker uses a local tuplesort to sort and merge the entries
for the same key. The TID lists do not overlap (for a given key), which
means the merge sort simply concatenates the two lists. The merged
entries are written into a shared tuplesort for the leader.
 
The leader needs to merge the sorted entries again, before writing them
into the index. But this way a significant part of the work happens in
the workers, and the leader is left with merging fewer large entries,
which is more efficient.
 
Most of the parallelism infrastructure is a simplified copy of the code
used by BTREE indexes, omitting the parts irrelevant for GIN indexes
(e.g. uniqueness checks).
 
Original patch by me, with reviews and substantial improvements by
Matthias van de Meent, certainly enough to make him a co-author.
 
Author: Tomas Vondra, Matthias van de Meent
Reviewed-by: Matthias van de Meent, Andy Fan, Kirill Reshke
Discussion: https://postgr.es/m/6ab4003f-a8b8-4d75-a67f-f25ad98582dc%40enterprisedb.com

Continue reading Waiting for PostgreSQL 18 – Allow parallel CREATE INDEX for GIN indexes

Waiting for PostgreSQL 18 – Allow EXPLAIN to indicate fractional rows.

On 21st of February 2025, Robert Haas committed patch:

Allow EXPLAIN to indicate fractional rows.
 
When nloops > 1, we now display two digits after the decimal point,
rather than none. This is important because what we print is actually
planstate->instrument->ntuples / nloops, and sometimes what you want
to know is planstate->instrument->ntuples. You can estimate that by
multiplying the displayed row count by the displayed nloops value, but
the fact that the displayed value is rounded makes that inexact. It's
still inexact even if we show these two extra decimal places, but less
so. Perhaps we will agree on a way to further improve this output later,
but for now this seems better than doing nothing.
 
Author: Ibrar Ahmed <ibrar.ahmad@gmail.com>
Author: Ilia Evdokimov <ilya.evdokimov@tantorlabs.com>
Reviewed-by: David G. Johnston <david.g.johnston@gmail.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Reviewed-by: Vignesh C <vignesh21@gmail.com>
Reviewed-by: Greg Stark <stark@mit.edu>
Reviewed-by: Naeem Akhter <akhternaeem@gmail.com>
Reviewed-by: Hamid Akhtar <hamid.akhtar@percona.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Andrei Lepikhov <a.lepikhov@postgrespro.ru>
Reviewed-by: Guillaume Lelarge <guillaume@lelarge.info>
Reviewed-by: Matheus Alcantara <matheusssilv97@gmail.com>
Reviewed-by: Alena Rybakina <a.rybakina@postgrespro.ru>
Discussion: http://postgr.es/m/603c8f070905281830g2e5419c4xad2946d149e21f9d%40mail.gmail.com

and then, 6 days later he also committed:

EXPLAIN: Always use two fractional digits for row counts.
Commit ddb17e387aa28d61521227377b00f997756b8a27 attempted to avoid
confusing users by displaying digits after the decimal point only when
nloops > 1, since it's impossible to have a fraction row count after a
single iteration. However, this made the regression tests unstable since
parallal queries will have nloops>1 for all nodes below the Gather or
Gather Merge in normal cases, but if the workers don't start in time and
the leader finishes all the work, they will suddenly have nloops==1,
making it unpredictable whether the digits after the decimal point would
be displayed or not. Although 44cbba9a7f51a3888d5087fc94b23614ba2b81f2
seemed to fix the immediate failures, it may still be the case that there
are lower-probability failures elsewhere in the regression tests.
Various fixes are possible here. For example, it has previously been
proposed that we should try to display the digits after the decimal
point only if rows/nloops is an integer, but currently rows is storead
as a float so it's not theoretically an exact quantity -- precision
could be lost in extreme cases. It has also been proposed that we
should try to display the digits after the decimal point only if we're
under some sort of construct that could potentially cause looping
regardless of whether it actually does. While such ideas are not
without merit, this patch adopts the much simpler solution of always
display two decimal digits. If that approach stands up to scrutiny
from the buildfarm and human users, it spares us the trouble of doing
anything more complex; if not, we can reassess.
This commit incidentally reverts 44cbba9a7f51a3888d5087fc94b23614ba2b81f2,
which should no longer be needed.
Author: Robert Haas <robertmhaas@gmail.com>
Author: Ilia Evdokimov <ilya.evdokimov@tantorlabs.com>
Discussion: http://postgr.es/m/CA+TgmoazzVHn8sFOMFAEwoqBTDxKT45D7mvkyeHgqtoD2cn58Q@mail.gmail.com

Continue reading Waiting for PostgreSQL 18 – Allow EXPLAIN to indicate fractional rows.

Waiting for PostgreSQL 18 – Virtual generated columns

On 7th of February 2025, Peter Eisentraut committed patch:

Virtual generated columns
This adds a new variant of generated columns that are computed on read
(like a view, unlike the existing stored generated columns, which are
computed on write, like a materialized view).
The syntax for the column definition is
... GENERATED ALWAYS AS (...) VIRTUAL
and VIRTUAL is also optional. VIRTUAL is the default rather than
STORED to match various other SQL products. (The SQL standard makes
no specification about this, but it also doesn't know about VIRTUAL or
STORED.) (Also, virtual views are the default, rather than
materialized views.)
Virtual generated columns are stored in tuples as null values. (A
very early version of this patch had the ambition to not store them at
all. But so much stuff breaks or gets confused if you have tuples
where a column in the middle is completely missing. This is a
compromise, and it still saves space over being forced to use stored
generated columns. If we ever find a way to improve this, a bit of
pg_upgrade cleverness could allow for upgrades to a newer scheme.)
The capabilities and restrictions of virtual generated columns are
mostly the same as for stored generated columns. In some cases, this
patch keeps virtual generated columns more restricted than they might
technically need to be, to keep the two kinds consistent. Some of
that could maybe be relaxed later after separate careful
considerations.
Some functionality that is currently not supported, but could possibly
be added as incremental features, some easier than others:
- index on or using a virtual column
- hence also no unique constraints on virtual columns
- extended statistics on virtual columns
- foreign-key constraints on virtual columns
- not-null constraints on virtual columns (check constraints are supported)
- ALTER TABLE / DROP EXPRESSION
- virtual column cannot have domain type
- virtual columns are not supported in logical replication
The tests in generated_virtual.sql have been copied over from
generated_stored.sql with the keyword replaced. This way we can make
sure the behavior is mostly aligned, and the differences can be
visible. Some tests for currently not supported features are
currently commented out.
Reviewed-by: Jian He <jian.universality@gmail.com>
Reviewed-by: Dean Rasheed <dean.a.rasheed@gmail.com>
Tested-by: Shlok Kyal <shlok.kyal.oss@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/a368248e-69e4-40be-9c07-6c3b5880b0a6@eisentraut.org

Continue reading Waiting for PostgreSQL 18 – Virtual generated columns

Waiting for PostgreSQL 18 – Add delay time to VACUUM/ANALYZE (VERBOSE) and autovacuum logs.

On 14th of February 2025, Nathan Bossart committed patch:

Add delay time to VACUUM/ANALYZE (VERBOSE) and autovacuum logs.
 
Commit bb8dff9995 added this information to the
pg_stat_progress_vacuum and pg_stat_progress_analyze system views.
This commit adds the same information to the output of VACUUM and
ANALYZE with the VERBOSE option and to the autovacuum logs.
 
Suggested-by: Masahiro Ikeda <ikedamsh@oss.nttdata.com>
Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Discussion: https://postgr.es/m/ZmaXmWDL829fzAVX%40ip-10-97-1-34.eu-west-3.compute.internal

Continue reading Waiting for PostgreSQL 18 – Add delay time to VACUUM/ANALYZE (VERBOSE) and autovacuum logs.

Waiting for PostgreSQL 18 – Add cost-based vacuum delay time to progress views.

On 11st of February 2025, Nathan Bossart committed patch:

Add cost-based vacuum delay time to progress views.
 
This commit adds the amount of time spent sleeping due to
cost-based delay to the pg_stat_progress_vacuum and
pg_stat_progress_analyze system views.  A new configuration
parameter named track_cost_delay_timing, which is off by default,
controls whether this information is gathered.  For vacuum, the
reported value includes the sleep time of any associated parallel
workers.  However, parallel workers only report their sleep time
once per second to avoid overloading the leader process.
 
Bumps catversion.
 
Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Co-authored-by: Nathan Bossart <nathandbossart@gmail.com>
Reviewed-by: Sami Imseih <samimseih@gmail.com>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-by: Masahiro Ikeda <ikedamsh@oss.nttdata.com>
Reviewed-by: Dilip Kumar <dilipbalaut@gmail.com>
Reviewed-by: Sergei Kornilov <sk@zsrv.org>
Discussion: https://postgr.es/m/ZmaXmWDL829fzAVX%40ip-10-97-1-34.eu-west-3.compute.internal

Continue reading Waiting for PostgreSQL 18 – Add cost-based vacuum delay time to progress views.

Waiting for PostgreSQL 18 – Support RN (roman-numeral format) in to_number().

On 22nd of January 2025, Tom Lane committed patch:

Support RN (roman-numeral format) in to_number().
 
We've long had roman-numeral output support in to_char(),
but lacked the reverse conversion.  Here it is.
 
Author: Hunaid Sohail <hunaidpgml@gmail.com>
Reviewed-by: Maciek Sakrejda <m.sakrejda@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Tomas Vondra <tomas@vondra.me>
Discussion: https://postgr.es/m/CAMWA6ybh4M1VQqpmnu2tfSwO+3gAPeA8YKnMHVADeB=XDEvT_A@mail.gmail.com

Continue reading Waiting for PostgreSQL 18 – Support RN (roman-numeral format) in to_number().

Waiting for PostgreSQL 18 – Add OLD/NEW support to RETURNING in DML queries.

On 16th of January 2025, Dean Rasheed committed patch:

Add OLD/NEW support to RETURNING in DML queries.
 
This allows the RETURNING list of INSERT/UPDATE/DELETE/MERGE queries
to explicitly return old and new values by using the special aliases
"old" and "new", which are automatically added to the query (if not
already defined) while parsing its RETURNING list, allowing things
like:
 
  RETURNING old.colname, new.colname, ...
 
  RETURNING old.*, new.*
 
Additionally, a new syntax is supported, allowing the names "old" and
"new" to be changed to user-supplied alias names, e.g.:
 
  RETURNING WITH (OLD AS o, NEW AS n) o.colname, n.colname, ...
 
This is useful when the names "old" and "new" are already defined,
such as inside trigger functions, allowing backwards compatibility to
be maintained -- the interpretation of any existing queries that
happen to already refer to relations called "old" or "new", or use
those as aliases for other relations, is not changed.
 
For an INSERT, old values will generally be NULL, and for a DELETE,
new values will generally be NULL, but that may change for an INSERT
with an ON CONFLICT ... DO UPDATE clause, or if a query rewrite rule
changes the command type. Therefore, we put no restrictions on the use
of old and new in any DML queries.
 
Dean Rasheed, reviewed by Jian He and Jeff Davis.
 
Discussion: https://postgr.es/m/CAEZATCWx0J0-v=Qjc6gXzR=KtsdvAE7Ow=D=mu50AgOe+pvisQ@mail.gmail.com

Continue reading Waiting for PostgreSQL 18 – Add OLD/NEW support to RETURNING in DML queries.

Waiting for PostgreSQL 18 – Allow changing autovacuum_max_workers without restarting.

On 6th of January 2025, Nathan Bossart committed patch:

Allow changing autovacuum_max_workers without restarting.
 
This commit introduces a new parameter named
autovacuum_worker_slots that controls how many autovacuum worker
slots to reserve during server startup.  Modifying this new
parameter's value does require a server restart, but it should
typically be set to the upper bound of what you might realistically
need to set autovacuum_max_workers.  With that new parameter in
place, autovacuum_max_workers can now be changed with a SIGHUP
(e.g., pg_ctl reload).
 
If autovacuum_max_workers is set higher than
autovacuum_worker_slots, a WARNING is emitted, and the server will
only start up to autovacuum_worker_slots workers at a given time.
If autovacuum_max_workers is set to a value less than the number of
currently-running autovacuum workers, the existing workers will
continue running, but no new workers will be started until the
number of running autovacuum workers drops below
autovacuum_max_workers.
 
Reviewed-by: Sami Imseih, Justin Pryzby, Robert Haas, Andres Freund, Yogesh Sharma
Discussion: https://postgr.es/m/20240410212344.GA1824549%40nathanxps13

Continue reading Waiting for PostgreSQL 18 – Allow changing autovacuum_max_workers without restarting.

Waiting for PostgreSQL 18 – Enable BUFFERS with EXPLAIN ANALYZE by default

On 11st of December 2024, David Rowley committed patch:

Enable BUFFERS with EXPLAIN ANALYZE by default
The topic of turning EXPLAIN's BUFFERS option on with the ANALYZE option
has come up a few times over the past few years. In many ways, doing this
seems like a good idea as it may be more obvious to users why a given
query is running more slowly than they might expect. Also, from my own
(David's) personal experience, I've seen users posting to the mailing
lists with two identical plans, one slow and one fast asking why their
query is sometimes slow. In many cases, this is due to additional reads.
Having BUFFERS on by default may help reduce some of these questions, and
if not, make it more obvious to the user before they post, or save a
round-trip to the mailing list when additional I/O effort is the cause of
the slowness.
The general consensus is that we want BUFFERS on by default with
ANALYZE. However, there were more than zero concerns raised with doing
so. The primary reason against is the additional verbosity, making it
harder to read large plans. Another concern was that buffer information
isn't always useful so may not make sense to have it on by default.
It's currently December, so let's commit this to see if anyone comes
forward with a strong objection against making this change. We have over
half a year remaining in the v18 cycle where we could still easily consider
reverting this if someone were to come forward with a convincing enough
reason as to why doing this is a bad idea.
There were two patches independently submitted to achieve this goal, one
by me and the other by Guillaume. This commit is a mix of both of these
patches with some additional work done by me to adjust various
additional places in the documentation which include EXPLAIN ANALYZE
output.
Author: Guillaume Lelarge, David Rowley
Reviewed-by: Robert Haas, Greg Sabino Mullane, Michael Christofides
Discussion: https://postgr.es/m/CANNMO++W7MM8T0KyXN3ZheXXt-uLVM3aEtZd+WNfZ=obxffUiA@mail.gmail.com

Continue reading Waiting for PostgreSQL 18 – Enable BUFFERS with EXPLAIN ANALYZE by default

Waiting for PostgreSQL 18 – Support LIKE with nondeterministic collations

On 27th of November 2024, Peter Eisentraut committed patch:

Support LIKE with nondeterministic collations
This allows for example using LIKE with case-insensitive collations.
There was previously no internal implementation of this, so it was met
with a not-supported error. This adds the internal implementation and
removes the error. The implementation follows the specification of
the SQL standard for this.
Unlike with deterministic collations, the LIKE matching cannot go
character by character but has to go substring by substring. For
example, if we are matching against LIKE 'foo%bar', we can't start by
looking for an 'f', then an 'o', but instead with have to find
something that matches 'foo'. This is because the collation could
consider substrings of different lengths to be equal. This is all
internal to MatchText() in like_match.c.
The changes in GenericMatchText() in like.c just pass through the
locale information to MatchText(), which was previously not needed.
This matches exactly Generic_Text_IC_like() below.
ILIKE is not affected. (It's unclear whether ILIKE makes sense under
nondeterministic collations.)
This also updates match_pattern_prefix() in like_support.c to support
optimizing the case of an exact pattern with nondeterministic
collations. This was already alluded to in the previous code.
(includes documentation examples from Daniel Vérité and test cases
from Paul A Jungwirth)
Reviewed-by: Jian He <jian.universality@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/700d2e86-bf75-4607-9cf2-f5b7802f6e88@eisentraut.org

Continue reading Waiting for PostgreSQL 18 – Support LIKE with nondeterministic collations

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Author: depesz