Re: Our naming of wait events is a disaster.

I wrote:
> Digging through the existing callers of SimpleLruInit, we have
> name control lock subdir
> "async" AsyncCtlLock "pg_notify"
> "clog" CLogControlLock "pg_xact"
> "commit_timestamp" CommitTsControlLock "pg_commit_ts"
> "multixact_member" MultiXactMemberControlLock "pg_multixact/members"
> "multixact_offset" MultiXactOffsetControlLock "pg_multixact/offsets"
> "oldserxid" OldSerXidLock "pg_serial"
> "subtrans" SubtransControlLock "pg_subtrans"

> After studying that list for awhile, it seems to me that we could
> do worse than to name the SLRUs to match their on-disk subdirectories,
> which are names that are already user-visible. So I propose these
> base names for the SLRUs:

> Notify
> Xact
> CommitTs
> MultiXactMember (or MultiXactMembers)
> MultiXactOffset (or MultiXactOffsets)
> Serial
> Subtrans

As POC for this, here's a draft patch to rename the "async" SLRU and
associated locks. If people are good with this then I'll go through
and do similarly for the other SLRUs.

A case could be made for doing s/async/notify/ more widely in async.c;
for instance it's odd that the struct protected by NotifyQueueLock
didn't get renamed to NotifyQueueControl. But that seems a bit out
of scope for the immediate problem, and anyway I'm not sure how far to
take it. I don't really want to rename async.c's externally-visible
functions, for instance. For the moment I just renamed symbols used
in the SimpleLruInit() call.

regards, tom lane