This adjusts a few places which were appending a string constant
containing spaces onto a StringInfo. We have appendStringInfoSpaces for
that job, so let's use that instead.
For the change to jsonb.c's add_indent() function, appendStringInfoString
was being called inside a loop to append 4 spaces on each loop. This
meant that enlargeStringInfo would get called once per loop. Here it
should be much more efficient to get rid of the loop and just calculate
the number of spaces with "level * 4" and just append all the spaces in
one go.
Here we additionally adjust the appendStringInfoSpaces function so it
makes use of memset rather than a while loop to apply the required spaces
to the StringInfo. One of the problems with the while loop was that it
was incrementing one variable and decrementing another variable once per
loop. That's more work than what's required to get the job done. We may
as well use memset for this rather than trying to optimize the existing
loop. Some testing has shown memset is faster even for very small sizes.
Discussion: https://postgr.es/m/CAApHDvp_rKkvwudBKgBHniNRg67bzXVjyvVKfX0G2zS967K43A@mail.gmail.com
There's plenty places in frontend code that could benefit from a
string buffer implementation. Some because it yields simpler and
faster code, and some others because of the desire to share code
between backend and frontend.
While there is a string buffer implementation available to frontend
code, libpq's PQExpBuffer, it is clunkier than stringinfo, it
introduces a libpq dependency, doesn't allow for sharing between
frontend and backend code, and has a higher API/ABI stability
requirement due to being exposed via libpq.
Therefore it seems best to just making StringInfo being usable by
frontend code. There's not much to do for that, except for rewriting
two subsequent elog/ereport calls into others types of error
reporting, and deciding on a maximum string length.
For the maximum string size I decided to privately define MaxAllocSize
to the same value as used in the backend. It seems likely that we'll
want to reconsider this for both backend and frontend code in the not
too far away future.
For now I've left stringinfo.h in lib/, rather than common/, to reduce
the likelihood of unnecessary breakage. We could alternatively decide
to provide a redirecting stringinfo.h in lib/, or just not provide
compatibility.
Author: Andres Freund
Reviewed-By: Kyotaro Horiguchi, Daniel Gustafsson
Discussion: https://postgr.es/m/20190920051857.2fhnvhvx4qdddviz@alap3.anarazel.de
David Rowley
Bruce Momjian
Peter Eisentraut
Andres Freund