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This is similar to the AIO channels functionality in Perlbal,
but implemented using semaphores to optimize for the uncontended
case.
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This improves maintainability in case MogileFS changest these
limits.
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Both hash_initialize and hash_insert may return NULL to indicate
allocation errors. So implement a mog_oom_if_null helper function to
destroy the process instead of attempting to continue and dereferencing
NULL pointers.
This may affect configurations with limited memory and lacking
overcommit; but is unlikely to trigger given the small memory footprint
of cmogstored.
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This will allow us to lookup devices for per-(mog)device I/O queues.
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Lines longer than 80 columns aren't readable on my screen
with gigantic fonts.
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This will allow us to do lookups for IO queues/semaphores before
we attempt to fstatat/stat a path.
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If the mogstored sidechannel is inactive (in HTTP-only mode), we should
still count the number of devices correctly to correctly scale the
number of worker threads.
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This simplifies code, reduces contention, and reduces the
chances of independent MogileFS instances (with one instance
of cmogstored) stepping over each other.
Most cmogstored deployments are single docroot (for a single
instance of MogileFS), however cmogstored supports multiple
docroots for some rare configurations and we support them here.
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I forgot why this bound was necessary, so add a comment
ensuring I do not forget again.
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Having too many acceptor threads does not help, as it leads to
lock contention in the accept syscalls and the EPOLL_CTL_ADD
paths. The fair FIFO ordering of _blocking_ accept/accept4
syscalls also means we trigger unnecessary task switching and
incur cache misses under high load.
Since it is almost impossible for the acceptor threads to
be stuck on disk I/O since
commit 832316624f7a8f44b3e1d78a8a7a62a399241840
("acceptor threads push directly into event queue")
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This will help ensure availability when new devices are added,
without additional user interaction to manually set aio_threads
via sidechannel.
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mog_fd_init enforces setting the correct type, so relegate
mog_fd_get to private usage inside fdmap.c
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libkqueue recently migrated to SourceForge and Debian 7.0 is
the new stable.
We still support Debian 6.0 and will likely support it for years to
come since CentOS 5.x remains supported.
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Users unfamiliar with autotools may not realize bootstraping
is required when building from git.
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Our use of chdir in this test confuses valgrind which may
create a temporary file.
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There's no reason to be referencing FDs for these acceptors
since they're infrequently accessed by svc, so this should
make our internals more consistent. This also removes our
use of mog_fd_get (outside of test code).
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We will key most client events by pid() and file descriptors,
as this is least ambiguous. There are some minor refactorings
to pass "struct mog_fd *" around as much as possible instead of
"struct mog_http *".
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This results in a small size reduction due to better alignment:
$ ~/linux/scripts/bloat-o-meter cmogstored.before cmogstored.after
add/remove: 0/0 grow/shrink: 2/2 up/down: 20/-56 (-36)
function old new delta
mog_http_get_open 1460 1476 +16
mog_chunk_init 65 69 +4
http_forward_in_progress 63 55 -8
mog_http_parse 27171 27123 -48
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It does not matter if the Content-MD5 comes from the trailer or
header, we process it the same way with the Ragel parser.
This is obvious when reading our code (and associated hunk
this commit changes) in http_put.c
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getpeername() does not work on unconnected sockets. For error-handling,
unconnected sockets is a fairly common occurrence, so we want to get
the address early on when we know the address is still valid.
For IPv4 addresses, this does not increase memory overhead at all. IPv6
addresses[1] does require an additional heap allocation, but it does not
need to be aligned since it is infrequently accessed. If IPv6 becomes
common, we may need to expand our per-client storage to 192 bytes (from
128) on 64-bit (or see if we may pack data more carefully).
[1] IPv6 addresses are rare with MogileFS, as MogileFS does not
currently support them.
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MogileFS currently does not support IPv6, but maybe one day
it will. When it does, we'll be ready.
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This will allow us to more easily handle error reporting for
IPv6 addresses and allow for consistent formatting of
stringified IP addresses.
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Linux device-mapper names show up as 'dm-0', 'dm-1' and so on.
This allows users to store MogileFS files on encrypted devices
using dm-crypt and perhaps other, similar tools.
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The generic "struct sockaddr" may be padded to be the same size
as "struct sockaddr_storage" (which is what we were trying to
avoid in the first place by uinsg mog_sockaddr). This change
makes no difference on GNU/Linux.
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We must set errno manually for die_errno() if posix_memalign fails
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This will allow easy use of memset to reset attributes in
between requests without clobbering more important data.
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Andrey Okunev noted undefined references on the MogileFS mailing
list when building cmogstored 1.2.1 on his 32-bit CentOS5 machine.
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This release only fixes an assertion failure during graceful shutdown
while MogileFS fsck is running with checksumming enabled.
This only affects users running fsck with checksumming enabled during a
graceful shutdown of cmogstored. For upgrading cmogstored it is
recommended to:
1) stop fsck on the trackers (via "mogadm fsck stop")
2) wait for all tracker queues to drain and stop sending
fsck traffic to the affected host. You may wish to
"!want 0 fsck" on all your trackers and wait for the
fsck workers to stop.
3) upgrade cmogstored (in place upgrade works)
There are also several code comment updates for internal
components of cmogstored which may interest potential hackers.
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We have a future!
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tls_rbuf allows us to avoid nearly all dynamic allocation
for common HTTP requests. However, the mog_rbuf structure
may be detached from TLS as necessary (and another one
allocated in its place) when the need arises.
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Avoiding heap allocations in common paths is important
to high performance server design; document this important
design decision.
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Items in the low-priority fsck queue could trigger a assertion failure
during graceful shutdown due to improper handling of the MOG_NEXT_IGNORE
state in mog_mgmt_quit_step().
However, using the fsck queue in graceful shutdown (which is
single-threaded) is probably a bad idea anyways, as the fsck digest
could monopolize other requests. So give no special handling to fsck
digest queries during graceful shutdown.
This only affects users running fsck with checksumming enabled during a
graceful shutdown of cmogstored. For checksums users, it is recommended
to stop fsck from the trackers and wait for all tracker queues to drain
before upgrading cmogstored (and using graceful shutdown on the old
cmogstored).
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cmogstored is pretty fast, but it could be faster.
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While we're at it, explain the use of cloexec.
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Despite having an extensive test suite and minimal room for user
error, giving users the options to back out of a hot upgrade may
be worth supporting.
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Many files were missed the first time around in
commit 37026af96dec638aa850d604003bf7218d90037d
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This is a new feature and needs to be documented.
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This fixes a missing prototype warning for cmogstored_exit()
when checking exit.c with sparse.
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The events field of struct epoll_event is a uint32_t, not int.
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The epoll_event.data union is 64-bits on 32-bit systems while
pointers are 32-bit. We only use 32-bits of that union, but
valgrind mistakenly complains about it (the kernel does not
care about the user-supplied data union at all).
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sizeof(buf) returns the size of the pointer if buf is a passed
parameter, even if it the function prototype dictates a fixed
size for buf as we do in mog_iou_write. While we're at it,
make our mog_iou_write buf parameter const.
This bug was introduced in:
commit a960a351b2248a196c91cdbf6256f98e1bc2ef37
"split iostat util% tracking from mountlist"
and never affected an official release of cmogstored.
This bug was caught while testing on a 32-bit GNU/Linux machine.
My normal 32-bit FreeBSD 9.0 environment did not catch this as
iostat on that platform only reports integer percentages and
does not need more than 4 bytes.
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Older glibc will return ENOMEM on mprotect() failures. This bug
was only fixed in 2011, so the long-term distros and old
installations may not have the necessary backports.
ref: http://www.sourceware.org/bugzilla/show_bug.cgi?id=386
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pthread_create may return EAGAIN as a temporary failure,
do not abort a running process if this is the case.
For the initial mountlist scan, we must retry indefinitely for
cmogstored to be usable. However, with our thread pools, we can
always run fewer threads (as long as there is at least one
thread per-pool).
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This is a tricky test and doesn't always succeed, since
it's hard to tell how many file descriptors glibc will
use internally.
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We want to favor ppoll over pselect, since ppoll is a better
interface and we can have a slightly smaller binary with fewer
dependencies.
While we're at it, use mog_sleep(-1) as an alias for
mog_selfwake_wait to further reduce binary size.
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We need to atomically enable interrupts and sleep with
the same syscall. Fortunately, using pselect (through
mog_sleep) allows that and is POSIX-compliant, so use
that.
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This will inform the user of why cmogstored may be slow
to start, since we need the mountlist to be populated at
startup.
We also throw a pthread_cancel() in there to load libgcc_s under
glibc, so we can avoid loading libgcc_s once we're under FD pressure.
This makes test/http_idle_expire.rb more reliable.
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DNS lookups cause webrick tests to fail or timeout. Our
tests should not have external network dependencies.
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A typo caused unnecessary DNS lookups when inheriting sockets.
While we're at it, fix another typo in the error message, too.
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This saves us a file descriptor in Linux, which provides
epoll_pwait in 2.6.19+ (and ppoll for 2.6.18, the oldest
kernel we support).
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