vibe.d + dpq2 + json trick

[Denis Feklushkin]

On Tuesday, 19 August 2025 at 14:09:09 UTC, Robert Schadek wrote:

> While working on other stuff I thought why should I have to 
> press the DB response into json in vibe at all, as Postgres can 
> generate json?

It would also be nice to measure the time it takes to get a 
response from Postgres.

As for me, Postgres server is too expensive resource for this 
work, even though this particular query works faster for some 
reason. Getting a result near to a "tabular binary form" from PG, 
we can convert it in into JSON on D side which code can work in 
parallel on several (or hundreds) servers.

> Looking into it, it turns out that libpg which is used by dpq2 
> returns json as a string.

Strictly speaking, PG supports two JSON types: json and jsonb 
("indexed" form of json with additional offset values). It might 
be worth experimenting with changing it to "jsonb" type to 
achieve performance improvement

> foreach(ref it; result) {
>   pIds ~= Person(it["id"].as!(long)());
> }

libpq calls "id"->col number conversion for each time here. This, 
of course, is fast, but...