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bees: drop bees_sync, we will not need it

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bees_sync() was an exception-trapping wrapper around fsync() which is
not needed in any of the contexts from which it was called:

	1.  dedupe operations implicitly flush the src data, so there is
	no need to call fsync() to do that twice.

	2.  crawl position is written to a temporary file and renamed
	over the original, which always forces a flush when the original
	exists.  On the first write, where there is no original, a
	crash would result in starting over with an empty or hole-filled
	beescrawl file, which is the initial state of bees.  There is also
	a long history of kernel bugs triggered by fsync() in this case.

	3.  we use unreadahead to trigger writeback for flushing the
	hash table to persistent storage.  Here is a space where we might
	use fsync after all, as part of bees_unreadahead's emulation of
	POSIX_FADV_DONTNEED, but we need to get read-once behavior from
	the scanner before we can use this capability.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This commit is contained in:
Zygo Blaxell 2022-11-26 22:45:24 -05:00
parent be9321cdb3
commit cc87125e41
2 changed files with 0 additions and 24 deletions
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23
src/bees.cc
View File

@ -214,17 +214,6 @@ BeesTooLong::operator=(const func_type &f)
return *this;
}
void
bees_sync(int fd)
{
Timer sync_timer;
BEESNOTE("syncing " << name_fd(fd));
BEESTOOLONG("syncing " << name_fd(fd));
DIE_IF_NON_ZERO(fsync(fd));
BEESCOUNT(sync_count);
BEESCOUNTADD(sync_ms, sync_timer.age() * 1000);
}
void
bees_readahead(int const fd, off_t offset, size_t size)
{
@ -481,7 +470,6 @@ BeesTempFile::make_copy(const BeesFileRange &src)
auto src_p = src.begin();
auto dst_p = begin;
bool did_block_write = false;
while (dst_p < end) {
auto len = min(BLOCK_SIZE_CLONE, end - dst_p);
BeesBlockData bbd(src.fd(), src_p, len);
@ -492,7 +480,6 @@ BeesTempFile::make_copy(const BeesFileRange &src)
BEESNOTE("copying " << src << " to " << rv << "\n"
"\tpwrite " << bbd << " to " << name_fd(m_fd) << " offset " << to_hex(dst_p) << " len " << len);
pwrite_or_die(m_fd, bbd.data().data(), len, dst_p);
did_block_write = true;
BEESCOUNT(tmp_block);
BEESCOUNTADD(tmp_bytes, len);
}
@ -501,16 +488,6 @@ BeesTempFile::make_copy(const BeesFileRange &src)
}
BEESCOUNTADD(tmp_copy_ms, copy_timer.age() * 1000);
if (did_block_write) {
#if 0
// There were a lot of kernel bugs leading to lockups.
// Most of them are fixed now.
// Unnecessary sync makes us slow, but maybe it has some robustness utility.
// TODO: make this configurable.
bees_sync(m_fd);
#endif
}
BEESCOUNT(tmp_copy);
return rv;
}

1
src/bees.h
View File

@ -882,7 +882,6 @@ extern const char *BEES_USAGE;
extern const char *BEES_VERSION;
extern thread_local default_random_engine bees_generator;
string pretty(double d);
void bees_sync(int fd);
void bees_readahead(int fd, off_t offset, size_t size);
void bees_unreadahead(int fd, off_t offset, size_t size);
string format_time(time_t t);