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Pre-calculate whether to slow down for too many level 0 files

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Summary: Currently in DBImpl::MakeRoomForWrite(), we do  "versions_->NumLevelFiles(0) >= options_.level0_slowdown_writes_trigger" to check whether the writer thread needs to slow down. However, versions_->NumLevelFiles(0) is slightly more expensive than we expected. By caching the result of the comparison when installing a new version, we can avoid this function call every time.

Test Plan:
make all check
Manually trigger this behavior by applying universal compaction style and make sure inserts are made slow after there are certain number of files.

Reviewers: haobo, kailiu, igor

Reviewed By: kailiu

CC: nkg-, leveldb

Differential Revision: https://reviews.facebook.net/D15141
This commit is contained in:
Siying Dong 2014-01-14 11:04:27 -08:00
parent 51dd21926c
commit fbbf0d1456
3 changed files with 13 additions and 2 deletions
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3
db/db_impl.cc
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@ -3166,8 +3166,7 @@ Status DBImpl::MakeRoomForWrite(bool force,
break;
} else if (
allow_delay &&
versions_->NumLevelFiles(0) >=
options_.level0_slowdown_writes_trigger) {
versions_->NeedSlowdownForNumLevel0Files()) {
// We are getting close to hitting a hard limit on the number of
// L0 files. Rather than delaying a single write by several
// seconds when we hit the hard limit, start delaying each

4
db/version_set.cc
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@ -1148,6 +1148,7 @@ VersionSet::VersionSet(const std::string& dbname,
num_levels_(options_->num_levels),
dummy_versions_(this),
current_(nullptr),
need_slowdown_for_num_level0_files(false),
compactions_in_progress_(options_->num_levels),
current_version_number_(0),
last_observed_manifest_size_(0),
@ -1199,6 +1200,9 @@ void VersionSet::AppendVersion(Version* v) {
current_->Unref();
}
current_ = v;
need_slowdown_for_num_level0_files =
(options_->level0_slowdown_writes_trigger >= 0 && current_ != nullptr &&
NumLevelFiles(0) >= options_->level0_slowdown_writes_trigger);
v->Ref();
// Append to linked list

8
db/version_set.h
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@ -250,6 +250,12 @@ class VersionSet {
// Return the current version.
Version* current() const { return current_; }
// A Flag indicating whether write needs to slowdown because of there are
// too many number of level0 files.
bool NeedSlowdownForNumLevel0Files() const {
return need_slowdown_for_num_level0_files;
}
// Return the current manifest file number
uint64_t ManifestFileNumber() const { return manifest_file_number_; }
@ -489,6 +495,8 @@ class VersionSet {
Version dummy_versions_; // Head of circular doubly-linked list of versions.
Version* current_; // == dummy_versions_.prev_
bool need_slowdown_for_num_level0_files;
// Per-level key at which the next compaction at that level should start.
// Either an empty string, or a valid InternalKey.
std::string* compact_pointer_;