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dag: limit max segment level to 4

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Summary:
This is based on fbsource data, building level 5 proves to be not useful.

This would save 300ms in the write path.

Reviewed By: sfilipco

Differential Revision: D23494505

fbshipit-source-id: ca795b4900af40dbfdaa463d36f3169413bf6a62
This commit is contained in:
Jun Wu 2020-09-04 12:18:55 -07:00 committed by Facebook GitHub Bot
parent b4adf0602f
commit e74133f0fa
1 changed files with 8 additions and 1 deletions
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9
eden/scm/lib/dag/src/iddag.rs
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@ -72,7 +72,13 @@ pub struct SyncableIdDag<'a, Store: GetLock> {
lock: <Store as GetLock>::LockT,
}
static DEFAULT_SEG_SIZE: usize = 16;
/// See benches/segment_sizes.rs (D16660078) for this choice.
const DEFAULT_SEG_SIZE: usize = 16;
/// Maximum meaningful level. 4 is chosen because it is good enough
/// for an existing large repo (level 5 is not built because it
/// cannot merge level 4 segments).
const MAX_MEANINGFUL_LEVEL: Level = 4;
impl IdDag<IndexedLogStore> {
/// Open [`IdDag`] at the given directory. Create it on demand.
@ -534,6 +540,7 @@ impl<Store: IdDagStore> IdDag<Store> {
max_level: Level,
) -> Result<usize> {
let mut total = 0;
let max_level = max_level.min(MAX_MEANINGFUL_LEVEL);
for level in 1..=max_level {
let count = self.build_high_level_segments(level, drop_last)?;
tracing::debug!("new lv{} segments: {}", level, count);