On Tue, May 11, 2021 at 5:38 PM Bharath Rupireddy <bharath.rupireddyforpostg...@gmail.com> wrote: > > Hi, > > I was going through the parallel vacuum docs and code. I found below > things, please someone clarify: > > 1) I see that a term "parallel degree" is used in the docs, code > comments, error messages "parallel vacuum degree must be a > non-negative integer", "parallel vacuum degree must be between 0 and > %d". Is there any specific reason to use the term "parallel degree"? > In the docs and code comments we generally use "parallel workers".
I think using "parallel workers" will be more consistent. > 2) The error messages "parallel vacuum degree must be between 0 and > %d" and "parallel option requires a value between 0 and %d" look > inconsistent. +1 > 3) Should the Assert(nindexes > 0); in begin_parallel_vacuum just be > Assert(nindexes > 1); as this function is entered only when indexes > are > 1? > 4) IIUC, below comment says that even if PARALLEL 0 is specified with > VACUUM command, there are chances that the indexes are vacuumed in > parallel. Isn't it a bit unusual that a user specified 0 workers but > still the system is picking up parallelism? I'm sure this would have > been discussed, but I'm curious to know the reason. > * nrequested is the number of parallel workers that user requested. If > * nrequested is 0, we compute the parallel degree based on nindexes, that is > * the number of indexes that support parallel vacuum. > 5) Can the parallel_workers in below condition ever be negative in > begin_parallel_vacuum? I think we can just have if (parallel_workers > == 0). > /* Can't perform vacuum in parallel */ > if (parallel_workers <= 0) Yes it should if (parallel_workers == 0) > 8) Is it still true that if parallel workers are specified as 0 the > parallelism will not be picked up? > From the docs: This feature is known as parallel vacuum. To disable > this feature, one can use PARALLEL option and specify parallel workers > as zero. Yes, by default this is enabled so for disabling user need to give PARALLEL as 0. -- Regards, Dilip Kumar EnterpriseDB: http://www.enterprisedb.com
