Re: pg_rewind WAL segments deletion pitfall

Here are my review comments:

@@ -217,6 +221,26 @@ findLastCheckpoint(const char *datadir, XLogRecPtr forkptr, int tliIndex,
+                       char            xlogfname[MAXFNAMELEN];
+
+                       tli = xlogreader->seg.ws_tli;
+                       segno = xlogreader->seg.ws_segno;
+
+                       snprintf(xlogfname, MAXPGPATH, XLOGDIR "/");
+                       XLogFileName(xlogfname + strlen(xlogfname),
+                                                xlogreader->seg.ws_tli,
+                                                xlogreader->seg.ws_segno, WalSegSz);
+
+                       /*
+                        * Make sure pg_rewind doesn't remove this file, because it is
+                        * required for postgres to start after rewind.
+                        */
+                       insert_keepwalhash_entry(xlogfname);

MAXFNAMELEN is 64 and MAXPGPATH is 1024. strlen(XLOGDIR "/")
is 7 because XLOGDIR is "pg_wal". So xlogfname has enough
size but snprintf(xlogfname, MAXPGPATH) is wrong usage.
(And XLogFileName() uses snprintf(xlogfname, MAXFNAMELEN)
internally.)