Lately at least two people on irc asked questions similar to “how do I know how many queries there are in database, per second?“.
So, let's see what we can find out.
Incrementing counters in database
Some time ago someone on irc asked about creating fast counters for something (banners I think).
I talked with her (him?) about it, but figured, I can as well write a blogpost, so others can use it too.
The hard math of killing zombies in Zombicide
I happen to play Zombicide. It's cooperative board game set in some kind of post-apocalyptic, zombie-infested, world.
Despite the general theme, lots of people like it, so we play it quite a lot.
One thing that bugged us, was : in given scenario, which weapon it's best to use?
Continue reading The hard math of killing zombies in Zombicide
Picking task from queue – revisit
Some time ago, I wrote blogpost about how to pick a task from queue, without locking.
It was written in 2013, and as such it couldn't reflect everything we have now in PostgreSQL – namely SKIP LOCKED – which was added to PostgreSQL over year later.
Two people mentioned SKIP LOCKED in comments, but it was before it was committed even to git repo. But now, we have, officially released, PostgreSQL version with this mechanism, so let's see what it can do.
Waiting for 9.6 – Support \crosstabview in psql
On 8th of April, Alvaro Herrera committed patch:
Support \crosstabview in psql \crosstabview is a completely different way to display results from a query: instead of a vertical display of rows, the data values are placed in a grid where the column and row headers come from the data itself, similar to a spreadsheet. The sort order of the horizontal header can be specified by using another column in the query, and the vertical header determines its ordering from the order in which they appear in the query. This only allows displaying a single value in each cell. If more than one value correspond to the same cell, an error is thrown. Merging of values can be done in the query itself, if necessary. This may be revisited in the future. Author: Daniel Verité <span class="signoff">Reviewed-by: Pavel Stehule, Dean Rasheed</span>
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Waiting for 9.6 – Phrase full text search.
On 7th of April, Teodor Sigaev committed patch:
Phrase full text search. Patch introduces new text search operator (<-> or <DISTANCE>) into tsquery. On-disk and binary in/out format of tsquery are backward compatible. It has two side effect: - change order for tsquery, so, users, who has a btree index over tsquery, should reindex it - less number of parenthesis in tsquery output, and tsquery becomes more readable Authors: Teodor Sigaev, Oleg Bartunov, Dmitry Ivanov Reviewers: Alexander Korotkov, Artur Zakirov
Waiting for 9.6 – Add a \gexec command to psql for evaluation of computed queries.
On 4th of April, Tom Lane committed patch:
Add a \gexec command to psql for evaluation of computed queries. \gexec executes the just-entered query, like \g, but instead of printing the results it takes each field as a SQL command to send to the server. Computing a series of queries to be executed is a fairly common thing, but up to now you always had to resort to kluges like writing the queries to a file and then inputting the file. Now it can be done with no intermediate step. The implementation is fairly straightforward except for its interaction with FETCH_COUNT. ExecQueryUsingCursor isn't capable of being called recursively, and even if it were, its need to create a transaction block interferes unpleasantly with the desired behavior of \gexec after a failure of a generated query (i.e., that it can continue). Therefore, disable use of ExecQueryUsingCursor when doing the master \gexec query. We can still apply it to individual generated queries, however, and there might be some value in doing so. While testing this feature's interaction with single-step mode, I (tgl) was led to conclude that SendQuery needs to recognize SIGINT (cancel_pressed) as a negative response to the single-step prompt. Perhaps that's a back-patchable bug fix, but for now I just included it here. Corey Huinker, reviewed by Jim Nasby, Daniel Vérité, and myself
Continue reading Waiting for 9.6 – Add a \gexec command to psql for evaluation of computed queries.
Waiting for 9.6 – Bloom index contrib module
On 1st of April, Teodor Sigaev committed patch:
Bloom index contrib module Module provides new access method. It is actually a simple Bloom filter implemented as pgsql's index. It could give some benefits on search with large number of columns. Module is a single way to test generic WAL interface committed earlier. Author: Teodor Sigaev, Alexander Korotkov Reviewers: Aleksander Alekseev, Michael Paquier, Jim Nasby
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Change on explain.depesz.com
As of now, main table that stores explain.depesz.com plans is partitioned.
This shouldn't be, at all, visible for users of the site, but if it would, please let me know (on irc, or via email).
In case you're wondering why, after all there is only ~ 270,000 plans – the reason is very simple. Splitting the data into multiple tables makes maintenance tasks (vacuum, dump) much simpler and easier.
Waiting for 9.6 – Support parallel aggregation.
On 21st of March, Robert Haas committed patch:
Support parallel aggregation. Parallel workers can now partially aggregate the data and pass the transition values back to the leader, which can combine the partial results to produce the final answer. David Rowley, based on earlier work by Haribabu Kommi. Reviewed by Álvaro Herrera, Tomas Vondra, Amit Kapila, James Sewell, and me.
Continue reading Waiting for 9.6 – Support parallel aggregation.