Discovering less-known Postgres v12 features

https://www.cybertec-postgresql.com/en/discovering-less-known-postgresql-12-features/

by samsk • 7 years ago

243 30 7 years ago

GordonS• 7 years ago

Wasn't aware of log_transaction_sample_rate - should be useful for not spamming the logs.

tbrock• 7 years ago

Inlining CTEs is a big deal but they also finally have a way to see the progress of an index build without a PhD in postgresology!

Check it out here: https://www.postgresql.org/docs/12/progress-reporting.html

bflesch• 7 years ago

This is worth a lot - thanks for the pointer!

barrkel• 7 years ago

I've found CTEs to be one of the few ways to reliably force Postgres evaluation order, which is sometimes quite poor (I have specific queries that run 100x faster with CTE), so retaining old behaviour with materialized is something I didn't know about in 12.

jeltz4• 7 years ago

How this should be done was the big roadblock, the actual inlining was a relatively simple patch.

paulddraper5• 7 years ago

My #1 request for indexes from PostgreSQL or 3rd party tool is concurrently rebuilding indexes.

I have had several cases where query performance dropped significantly (unfortunately in managed AWS Aurora DB, so I have limited inspection abilities).

Index rebuilds is the solution but it locks the entire table.

You can get a concurrent rebuild by creating a new index concurrently, then transactionally drop the old one and rename the new one. It's error prone though.

merb• 7 years ago

You can get a concurrent rebuild by creating a new index concurrently, then transactionally drop the old one and rename the new one. It's error prone though.

actually you can't since you can't create/drop indexes concurrently inside a transaction.

btw. my #1 request would be a better materialized view (which supports indexes) and also makes the performane of some stuff really better. unfortunatly you can't refresh it without a full seq scan. it would be great if postgres would have an auto updating materialized view.

mslot• 7 years ago

PostgreSQL 12 has REINDEX CONCURRENTLY.

jeltz4• 7 years ago

You will need to pick a new #1 request since PostgreSQL 12 finally delivered REINDEX CONCURRENTLY. :)

macdice• 7 years ago

One nice thing about the CTE inlining its that materialised CTEs were stopping parallelism from being used. WITH is useful in big OLAP queries, where parallelisms should really help.

megous• 7 years ago

OTOH, it slowed down one of my queries from a few ms to 3s just by upgrading. So it's not some magic absolute benefit.

I had to go and add "materialized" to a few places.

jeltz4• 7 years ago

Yeah, if the planner estimates are bad the inlining can produce a worse query plan.

cdcarter• 7 years ago

SQL/JSON path expressions look very powerful for making queries easier to understand, they’re a part of the SQL spec I hadn’t seen yet.

I’m a little sad though to see yet another JSON location mini-language appear. We’ve got JSONPointer (IETF standard for the web, used by jsonschema), JSONPath, the more expressive but cross language JMESPath, the CLI favorite jq, and presumably a billion more. It’s wearing me out.

zonidjan• 7 years ago

Site blocking the page with an empty overlay named "BorlabsCookie". No thanks.

tln• 7 years ago

The cookie acceptance on this site is as good as it gets IMO. Clear, detailed, privacy policies linked, with the ability to accept a reasonable, minimal subset.

Boulth4• 7 years ago

Are there any good advanced SQL books out there?

Shish2k• 7 years ago

As someone who spent the past week working on database abstractions, I'm pretty sure this is impossible - you can find Basic SQL books, and you can find Advanced Postgres / Advanced MySQL / Advanced Oracle :P

The basic book would pretty much just cover "select * from table". Everything beyond that, for instance "select * from table limit 10", is implementation-specific...

(I'm not even exaggerating: https://en.wikibooks.org/wiki/SQL_Dialects_Reference/Select_... )

Boulth4• 7 years ago

That's what I was afraid of but still asked if there is Advanced ANSI SQL book.

Thanks!

mark_h• 7 years ago

Probably not what you're asking, but this book is fantastic: https://sql-performance-explained.com/

Edit: and topically, free for the weekend! https://twitter.com/MarkusWinand/status/1199982940471607297

Boulth4• 7 years ago

Not what I were asking about but definitely something that I need. Thanks a lot for the reference and wow, lucky timing!

purerandomness• 7 years ago

I found Dimitri Fontaine's https://theartofpostgresql.com/ advanced. Learned lots of new tricks out of it.

Boulth4• 7 years ago

Looks nice and it's on discount because of Black Friday. Thanks!

Deimorz• 7 years ago

It was added in 11, but I want to mention again how great of an addition the websearch_to_tsquery() function was. You can now get a respectable search system immediately in PostgreSQL without having to implement any sort of query-parsing or special data indexing yourself. All you need to do is add a column/index for fulltext search, which you can even do now using the generated columns added in 12 (instead of a trigger).

Then just pass user-entered queries through websearch_to_tsquery() and have access to multiple search capabilities easily. It supports searching for alternatives with "or", phrases in quotes, and excluding terms with a minus sign, which is all syntax that a lot of people are already used to. For example it can handle a query like:

    blizzard or overwatch -"hong kong"

That would find anything with "blizzard" or "overwatch" in it, but exclude anything with "hong kong" (if you wanted to avoid results about that recent controversy).

It's really useful, and makes it so that you can add reasonable search functionality with almost no work at all.

ComputerGuru• 7 years ago

That is really cool and definitely a massive timesaver (I've written my own primitive query NLP for SQLite fstext indices and can definitely appreciate this feature!)

That said, (and only because your example reminded me) I absolutely hate the NLP `or` operator. I feel like any language to offer an `or` operator needs to require the simultaneous usage of a grouping operator (parentheses, etc.) to clarify the order of operations. A space is an implicit `and` so I never know if the `or` is working on directly adjacent keywords or the query as a whole.

Discovering less-known Postgres v12 features

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