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In-place updates for equal keys and similar sized values

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Summary:
Currently for each put, a fresh memory is allocated, and a new entry is added to the memtable with a new sequence number irrespective of whether the key already exists in the memtable. This diff is an attempt to update the value inplace for existing keys. It currently handles a very simple case:
1. Key already exists in the current memtable. Does not inplace update values in immutable memtable or snapshot
2. Latest value type is a 'put' ie kTypeValue
3. New value size is less than existing value, to avoid reallocating memory

TODO: For a put of an existing key, deallocate memory take by values, for other value types till a kTypeValue is found, ie. remove kTypeMerge.
TODO: Update the transaction log, to allow consistent reload of the memtable.

Test Plan: Added a unit test verifying the inplace update. But some other unit tests broken due to invalid sequence number checks. WIll fix them next.

Reviewers: xinyaohu, sumeet, haobo, dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D12423

Automatic commit by arc
This commit is contained in:
Naman Gupta
2013-08-19 14:12:47 -07:00
parent 17991cd5a0
commit fe25070242
12 changed files with 212 additions and 21 deletions
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3
db/write_batch_test.cc
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@@ -25,7 +25,8 @@ static std::string PrintContents(WriteBatch* b) {
MemTable* mem = new MemTable(cmp, factory);
mem->Ref();
std::string state;
Status s = WriteBatchInternal::InsertInto(b, mem);
Options options;
Status s = WriteBatchInternal::InsertInto(b, mem, &options);
int count = 0;
Iterator* iter = mem->NewIterator();
for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {