On Sun, 18 Feb 2001, Tom Lane wrote:
> I think that there may be a performance advantage to pre-filling the
> logfile even so, assuming that file allocation info is stored in a
> Berkeley/McKusik-like fashion (note: I have no idea what ext2 or
> reiserfs actually do).
ext2 is a lot like [UF]FS. reiserfs is very different, but does
have similar hole semantics.
BTW, I have attached two patches which streamline log initialisation
a little. The first (xlog-sendfile.diff) adds support for Linux's
sendfile system call. FreeBSD and HP/UX have sendfile() too, but the
prototype is different. If it's interesting, someone will have to
come up with a configure test, as autoconf scares me.
The second removes a further three syscalls from the log init path.
There are a couple of things to note here:
* I don't know why link/unlink is currently preferred over
rename. POSIX offers strong guarantees on the semantics
of the latter.
* I have assumed that the close/rename/reopen stuff is only
there for the benefit of Windows users, and ifdeffed it
for everyone else.
Matthew.
--- xlog.c.old Mon Feb 19 12:35:53 2001
+++ xlog.c Mon Feb 19 13:05:23 2001
@@ -24,6 +24,10 @@
#include <locale.h>
#endif
+#ifdef _HAVE_LINUX_SENDFILE
+#include <sys/sendfile.h>
+#endif
+
#include "access/transam.h"
#include "access/xact.h"
#include "catalog/catversion.h"
@@ -962,6 +966,24 @@
elog(STOP, "InitCreate(logfile %u seg %u) failed: %m",
logId, logSeg);
+#ifdef _HAVE_LINUX_SENDFILE
+ {
+ static int zfd = -1;
+ ssize_t len;
+
+ if (zfd < 0) {
+ zfd = BasicOpenFile("/dev/zero", O_RDONLY, 0);
+ if (zfd < 0)
+ elog(STOP, "Can't open /dev/zero: %m");
+ }
+ len = sendfile(fd, zfd, NULL, XLogSegSize);
+ if (len < 0)
+ /* XXX - header support sendfile, but kernel doesn't? Fall
+back */
+ elog(STOP, "sendfile failed: %m");
+ if (len < XLogSegSize)
+ elog(STOP, "short read on sendfile: %m");
+ }
+#else
if (lseek(fd, XLogSegSize - 1, SEEK_SET) != (off_t) (XLogSegSize - 1))
elog(STOP, "lseek(logfile %u seg %u) failed: %m",
logId, logSeg);
@@ -969,6 +991,7 @@
if (write(fd, "", 1) != 1)
elog(STOP, "write(logfile %u seg %u) failed: %m",
logId, logSeg);
+#endif
if (pg_fsync(fd) != 0)
elog(STOP, "fsync(logfile %u seg %u) failed: %m",
--- xlog.c.sf Mon Feb 19 13:10:38 2001
+++ xlog.c Mon Feb 19 13:13:55 2001
@@ -1001,22 +1001,20 @@
elog(STOP, "lseek(logfile %u seg %u off %u) failed: %m",
log, seg, 0);
+#ifndef WIN32
close(fd);
+#endif
-#ifndef __BEOS__
- if (link(tpath, path) < 0)
-#else
if (rename(tpath, path) < 0)
-#endif
elog(STOP, "InitRelink(logfile %u seg %u) failed: %m",
logId, logSeg);
- unlink(tpath);
-
+#ifndef WIN32
fd = BasicOpenFile(path, O_RDWR | PG_BINARY, S_IRUSR | S_IWUSR);
if (fd < 0)
elog(STOP, "InitReopen(logfile %u seg %u) failed: %m",
logId, logSeg);
+#endif
return (fd);
}
