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Compaction now conditionally boosts the size of deletion entries.

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Summary:
Compaction now boosts the size of deletion entries of a file only when
the number of deletion entries is greater than the number of non-deletion
entries in the file.  The motivation here is that in a stable workload,
the number of deletion entries should be roughly equal to the number of
non-deletion entries.  If we compensate the size of deletion entries in a
stable workload, the deletion compensation logic might introduce unwanted
effet which changes the shape of LSM tree.

Test Plan: db_test --gtest_filter="*Deletion*"

Reviewers: sdong, igor

Reviewed By: igor

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D38703
This commit is contained in:
Yueh-Hsuan Chiang 2015-05-26 14:05:38 -07:00
parent a81ac24127
commit 3ab8ffd4dd
1 changed files with 14 additions and 3 deletions
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17
db/version_set.cc
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@ -962,9 +962,20 @@ void VersionStorageInfo::ComputeCompensatedSizes() {
// for files that have been created right now and no other thread has
// access to them. That's why we can safely mutate compensated_file_size.
if (file_meta->compensated_file_size == 0) {
file_meta->compensated_file_size = file_meta->fd.GetFileSize() +
file_meta->num_deletions * average_value_size *
kDeletionWeightOnCompaction;
file_meta->compensated_file_size = file_meta->fd.GetFileSize();
// Here we only boost the size of deletion entries of a file only
// when the number of deletion entries is greater than the number of
// non-deletion entries in the file. The motivation here is that in
// a stable workload, the number of deletion entries should be roughly
// equal to the number of non-deletion entries. If we compensate the
// size of deletion entries in a stable workload, the deletion
// compensation logic might introduce unwanted effet which changes the
// shape of LSM tree.
if (file_meta->num_deletions * 2 >= file_meta->num_entries) {
file_meta->compensated_file_size +=
(file_meta->num_deletions * 2 - file_meta->num_entries)
* average_value_size * kDeletionWeightOnCompaction;
}
}
}
}