Re: pgsql: Modify pg_basebackup to use a new COPY subprotocol for base back

I wrote:
>> Tom, any chance you can get a stack trace?

> Hmm, I'd assumed that was just a cosmic ray or something.

My mistake: it's failing because of -fsanitize=alignment.

Here's the stack trace:

  * frame #0: 0x000000010885dfd0 postgres`sendFile(sink=0x00007fdedf071cb0, readfilename="./global/4178",
tarfilename="global/4178",statbuf=0x00007ffee77dfaf8, missing_ok=true, dboid=0, manifest=0x00007ffee77e2780,
spcoid=0x0000000000000000)at basebackup.c:1552:10 
    frame #1: 0x000000010885cb7f postgres`sendDir(sink=0x00007fdedf071cb0, path="./global", basepathlen=1,
sizeonly=false,tablespaces=0x00007fdedf072718, sendtblspclinks=true, manifest=0x00007ffee77e2780,
spcoid=0x0000000000000000)at basebackup.c:1354:12 
    frame #2: 0x000000010885ca6b postgres`sendDir(sink=0x00007fdedf071cb0, path=".", basepathlen=1, sizeonly=false,
tablespaces=0x00007fdedf072718,sendtblspclinks=true, manifest=0x00007ffee77e2780, spcoid=0x0000000000000000) at
basebackup.c:1346:13
    frame #3: 0x00000001088595be postgres`perform_base_backup(opt=0x00007ffee77e2e68, sink=0x00007fdedf071cb0) at
basebackup.c:352:5
    frame #4: 0x0000000108856b0b postgres`SendBaseBackup(cmd=0x00007fdedf05b510) at basebackup.c:932:3
    frame #5: 0x00000001088711c8 postgres`exec_replication_command(cmd_string="BASE_BACKUP ( LABEL 'pg_basebackup base
backup', PROGRESS,  CHECKPOINT 'fast',  MANIFEST 'yes',  TARGET 'client')") at walsender.c:1734:4 [opt] 
    frame #6: 0x00000001088dd61e postgres`PostgresMain(dbname=<unavailable>, username=<unavailable>) at
postgres.c:4494:12[opt] 

It failed at

-> 1552                                 if (!PageIsNew(page) && PageGetLSN(page) < sink->bbs_state->startptr)

and the problem is evidently that the page pointer isn't nicely aligned:

(lldb) p page
(char *) $4 = 0x00007fdeded7e041 ""

(I checked the "sink" data structure too for luck, but it seems fine.)

I see that thorntail has now also fallen over, presumably for
the same reason.

            regards, tom lane