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Simplify do_pg_start_backup's API by opening pg_tblspc internally.

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do_pg_start_backup() expects its callers to pass in an open DIR pointer
for the pg_tblspc directory, but there's no apparent advantage in that.
It complicates the callers without adding any flexibility, and there's no
robustness advantage, since we surely have to be prepared for errors during
the scan of pg_tblspc anyway.  In fact, by holding an extra kernel resource
during operations like the preliminary checkpoint, we might be making
things a fraction more failure-prone not less.  Hence, remove that argument
and open the directory just for the duration of the actual scan.

Discussion: https://postgr.es/m/28752.1512413887@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2017-12-04 18:37:54 -05:00
parent 561885db05
commit 066bc21c0e
4 changed files with 11 additions and 31 deletions
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15
src/backend/access/transam/xlogfuncs.c
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@ -75,7 +75,6 @@ pg_start_backup(PG_FUNCTION_ARGS)
bool exclusive = PG_GETARG_BOOL(2);
char *backupidstr;
XLogRecPtr startpoint;
DIR *dir;
SessionBackupState status = get_backup_status();
backupidstr = text_to_cstring(backupid);
@ -85,18 +84,10 @@ pg_start_backup(PG_FUNCTION_ARGS)
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("a backup is already in progress in this session")));
/* Make sure we can open the directory with tablespaces in it */
dir = AllocateDir("pg_tblspc");
if (!dir)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not open directory \"%s\": %m",
"pg_tblspc")));
if (exclusive)
{
startpoint = do_pg_start_backup(backupidstr, fast, NULL, NULL,
dir, NULL, NULL, false, true);
NULL, NULL, false, true);
}
else
{
@ -112,13 +103,11 @@ pg_start_backup(PG_FUNCTION_ARGS)
MemoryContextSwitchTo(oldcontext);
startpoint = do_pg_start_backup(backupidstr, fast, NULL, label_file,
dir, NULL, tblspc_map_file, false, true);
NULL, tblspc_map_file, false, true);
before_shmem_exit(nonexclusive_base_backup_cleanup, (Datum) 0);
}
FreeDir(dir);
PG_RETURN_LSN(startpoint);
}