On Tue, 29 Aug 2017, zengran zhang wrote:
> hi Sage,
> I want to ask when will the bluefs log be compacted? I only sure
> it will be compacted when umount the bluefs...
> I see the log be compact when rocksdb call Dir.Fsync(), but want to
> know how to trigger this...
There is a heuristic for when it gets "too big":
bool BlueFS::_should_compact_log()
{
uint64_t current = log_writer->file->fnode.size;
uint64_t expected = _estimate_log_size();
float ratio = (float)current / (float)expected;
dout(10) << __func__ << " current 0x" << std::hex << current
<< " expected " << expected << std::dec
<< " ratio " << ratio
<< (new_log ? " (async compaction in progress)" : "")
<< dendl;
if (new_log ||
current < cct->_conf->bluefs_log_compact_min_size ||
ratio < cct->_conf->bluefs_log_compact_min_ratio) {
return false;
}
return true;
}
and the estimate for the (compacted) size is
uint64_t BlueFS::_estimate_log_size()
{
int avg_dir_size = 40; // fixme
int avg_file_size = 12;
uint64_t size = 4096 * 2;
size += file_map.size() * (1 + sizeof(bluefs_fnode_t));
for (auto& p : block_all)
size += p.num_intervals() * (1 + 1 + sizeof(uint64_t) * 2);
size += dir_map.size() + (1 + avg_dir_size);
size += file_map.size() * (1 + avg_dir_size + avg_file_size);
return ROUND_UP_TO(size, super.block_size);
}
The default min_ratio is 5... so we compact when it's ~5x bigger than it
needs to be.
sage
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