Re: Is there a good discussion of optimizations?

[Rob Sargent <robjsargent@xxxxxxxxx>]

On 1/7/21 2:48 PM, Guyren Howe wrote:

On Jan 7, 2021, 13:42 -0800, Florents Tselai <florents.tselai@xxxxxxxxx>, wrote:

Apologies for the shameless self-promotion :) 

Around a year ago I collected my thoughts on this topic. You can read the post here Modern Data Practice and the SQL Tradition .

It looks like it resonated with a lot of folks in the community. HN Discussion https://news.ycombinator.com/item?id=21482114

I would specifically underline the fact that the newer generation of programmers & data pros (my former self included) don't really appreciate things like triggers and server-side programming. Triggers and DB-side functions are considered something like Assembly code. 

Not many neophytes have been shown with use cases why for example writing 2-3 lines of PL/SQL can save you a huge overhead of back and forth and environment set up to write the same thing in say Pandas. 

I would focus on Triggers, Indices on expressions, and time-related functions. Probably on generated columns too. They may be considered a new feature, but the reasoning of building successively columns on top of a few base ones is quite appealing nowadays, especially for ML purposes.

I also wouldn't hesitate to discuss advanced topics. They are usually considered obscure because people don't present useful examples, rather toy and arbitrary ones. 

In a recent O'Reilly training, I was skeptical of talking about triggers for optimization but it looks like it was probably the most useful part of my training as students could actually "steal and tweak" my code.

Thanks for this. May I steal some of your examples if they prove useful? I’ll credit you of course.

I’m planning on somewhat emphasizing that a relational database is a logic engine. Viewed through this lens, a query or view is a “backward” implication and a trigger is a “forward” one. This leads to considering triggers (and the moral equivalent in external code) as requiring “truth maintenance”, and is a great way to think about when the database is the appropriate place for some bit of logic.

On Thu, Jan 7, 2021 at 11:21 PM Guyren Howe <guyren@xxxxxxxxx> wrote:

On Jan 7, 2021, 13:07 -0800, Kevin Brannen <KBrannen@xxxxxxxx>, wrote:

From: Guyren Howe <guyren@xxxxxxxxx>

 

>Most folks, in my experience, who use relational databases don’t really understand the basic theory or even more important the why - the philosophy - of what a relational database is and how to get the most out of them. I see a lot of folks trying to use SQL in an imperative manner - make this temp table, then update it some, then make this other temp table, etc...

Actually, I’m mostly going to talk about the relational model, rather than SQL. Our industry seems to always settle for third-best, and SQL is the worst of all the examples of this. The world desperately needs a good relational database based on a better query language — datalog, for example.

I put up with SQL so I can use the relational model, and I think that understanding SQL has to start with that.

Anyhow.

An example of this is that we have a report we're trying to write that I'd

like to think can be done in SQL, but I can't think of a way to do it. Yet,

if I do the base query and pull the data back into my application, I can do

the last bit with 3 lines of Perl very easily. The problem here revolves

around comparing a row of data to the previous row to know whether the data

changed "significantly enough" to keep the new row.

 

Another example is doing running totals. A couple of years ago I would have

said SQL can't do that. Now I know about the OVER clause, something that I

would categorize as somewhat obscure, I can do it as needed.

Actually, Window functions might be “advanced”, but are certainly not obscure. Your example sounds like it’s trivially solved with LAG().

As Michael Lewis pointed out, large dataset can also cause you to choose not

to use SQL in 1 big statemet for everything (i.e. advocating the use to temp

tables). In some ways, using a CTE is a type of temp table, or at least I

view it as such. That allows a person to solve a problem in bite-sized chunks.

I will agree that optimization can do it better at times, but the code also has

to be maintained as well – a balancing act.

This appears to be good advice with SQL Server, which I’m coming to learn has a fairly poor query optimizer. But I would have thought Postgres’s optimizer would usually use a temporary table where appropriate.

    Please include, for all those front-end coders who might want to hit
    the database, the expense/overhead involved.   I've seen "foreach
    id, read database, process record" all too often.