Hello.
I tested dovecot's work with expunge messages on Mdbox over strace (see at tail of message). As I can see dovecot process opens old storage m.* file, reads it content, opens new temporary file, writes in this one content and rename this new one to m.(*+1).
How fast this algorithm works on system with about 10000 users and 5Tb data? I will use mdbox_rotate_interval for delayed expunge but I think that simple delete file in Maildir must be faster than expunge from Mdbox.
Please, tell me about real experience work with Mdbox on big loaded systems.
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0.000017open("/var/vmail/example.org/user/storage/.temp.1362474108.P7152Q0M909647.mailsys", O_RDWR|O_CREAT|O_TRUNC, 0666) = 11 0.000063 umask(077) = 066 0.000015 fallocate(11, 01, 0, 10485760) = 0 0.000054 fstat(11, {st_mode=S_IFREG|0600, st_size=0, ...}) = 0 0.000043 pread(10, "\1\2N 0000000000000285\nFC"..., 8192, 16) = 1465 0.000025 write(11, "2 M1e C5135b47c\n\1\2N 000"..., 691) = 691 0.000041 stat("/var/vmail/example.org/user/indexes/storage/dovecot.map.index.log.2", 0x7fff235b34c0) = -1 ENOENT (No such file or directory) 0.000026 alarm(180) = 0 0.000018 fcntl(9, F_SETLKW, {type=F_WRLCK, whence=SEEK_SET, start=0, len=0}) = 0 0.000020 alarm(0) = 180 0.000018 stat("/var/vmail/example.org/user/indexes/storage/dovecot.map.index.log", {st_mode=S_IFREG|0600, st_size=3656, ...}) = 0 0.000031 fstat(9, {st_mode=S_IFREG|0600, st_size=3656, ...}) = 0 0.000041 write(11, "\n\1\3\nR5135ad97\nV29b\nG5840870697ad"..., 62) = 62 0.000023 fdatasync(11) = 0 0.079275 stat("/var/vmail/example.org/user/storage/m.8", 0x7fff235b3640) = -1 ENOENT (No such file or directory) 0.000061 rename("/var/vmail/example.org/user/storage/.temp.1362474108.P7152Q0M909647.mailsys", "/var/vmail/example.org/user/storage/m.8") = 0 0.000164 write(9, "\200\200\200\203\0\0\10\20\210\0\0\0\200\200\200\207@\0\0\20\0\0\0\0\0\0\0\0\10\0\0\0"..., 152) = 152 0.000094 fcntl(9, F_SETLK, {type=F_UNLCK, whence=SEEK_SET, start=0, len=0}) = 0 0.000042 unlink("/var/vmail/example.org/user/storage/m.7") = 0 0.000059 stat("/var/vmail/example.org/user/indexes/storage/dovecot.map.index.log", {st_mode=S_IFREG|0600, st_size=3808, ...}) = 0 0.000055 fstat(9, {st_mode=S_IFREG|0600, st_size=3808, ...}) = 0