Plugin: sync

• infos = Information about the sync plugin is in keys below
• infos/author = Markus Raab elekt.nosp@m.ra@l.nosp@m.ibele.nosp@m.ktra.nosp@m..org
• infos/licence = BSD
• infos/provides = sync
• infos/needs =
• infos/placements = precommit
• infos/status = recommended productive maintained tested nodep libc final
• infos/description = Makes sure that config file is written to disc

Introduction

Storage plugins usually do not use fsync (2) for writing their file to disc. That means that the content of the file could be in some buffer and not on the hard disc.

This is good for power saving on laptops, but not a good idea on production use otherwise. So it is strongly recommended to always add this plugin.

Usage

Just add this plugin to the list of plugins during mounting, e.g.

kdb mount file.dump /important dump sync

Then when you observe the change of a value, e.g.

strace kdb set user:/important/key value

you can see, done by storage:

open("/home/markus/.kdb/file.dump.16874:1409592592.95084.tmp",
        O_WRONLY|O_CREAT|O_TRUNC, 0666) = 4
write(4, "kdbOpen 1\n", 10)             = 10
write(4, "ksNew 1\n", 8)                = 8
write(4, "keyNew 19 6\n", 12)           = 12
write(4, "user:/important/key\0value\0\n", 26) = 26
write(4, "keyEnd\n", 7)                 = 7
write(4, "ksEnd\n", 6)                  = 6
close(4)                                = 0

then done by sync:

open("/home/markus/.kdb/file.dump.16874:1409592592.95084.tmp",
        O_RDWR) = 4
fsync(4)                                = 0
close(4)                                = 0

and finally commit + sync of directory by resolver:

rename("/home/markus/.kdb/file.dump.16874:1409592592.95084.tmp",
        "/home/markus/.kdb/file.dump") = 0
stat("/home/markus/.kdb/file.dump", {st_mode=S_IFREG|0644,
        st_size=69, ...}) = 0
fcntl(3, F_SETLK, {type=F_UNLCK, whence=SEEK_SET, start=0,
        len=0}) = 0
close(3)                                = 0
open("/home/markus/.kdb",
        O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
fsync(3)                                = 0