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WritePrepared: followup fix for snapshot double release issue (#4734) 

Summary:
The fix in #4727 for double snapshot release was incomplete since it does not properly remove the duplicate entires in the snapshot list after finding that a snapshot is still valid. The patch does that and also improves the unit test to show the issue.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4734

Differential Revision: D13266260

Pulled By: maysamyabandeh

fbshipit-source-id: 351e2c40cca45a87b757774c11af74182314911e
This commit is contained in:
Maysam Yabandeh 2018-11-29 20:59:52 -08:00 committed by Facebook Github Bot
parent cf1df5d3cb
commit f1b0841f06
2 changed files with 27 additions and 3 deletions
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21
utilities/transactions/write_prepared_transaction_test.cc
View File

@ -747,7 +747,8 @@ TEST_P(WritePreparedTransactionTest, DoubleSnapshot) {
ASSERT_OK(txn->SetName("txn"));
ASSERT_OK(txn->Put("key", "value2"));
ASSERT_OK(txn->Prepare());
// Two snapshots with the same seq number
// Three snapshots with the same seq number
const Snapshot* snapshot0 = wp_db->GetSnapshot();
const Snapshot* snapshot1 = wp_db->GetSnapshot();
const Snapshot* snapshot2 = wp_db->GetSnapshot();
ASSERT_OK(txn->Commit());
@ -755,7 +756,11 @@ TEST_P(WritePreparedTransactionTest, DoubleSnapshot) {
SequenceNumber overlap_seq = txn->GetId() + cache_size;
delete txn;
// 4th snapshot with a larger seq
const Snapshot* snapshot3 = wp_db->GetSnapshot();
// Cause an eviction to advance max evicted seq number
// This also fetches the 4 snapshots from db since their seq is lower than the
// new max
wp_db->AddCommitted(overlap_seq, overlap_seq);
ReadOptions ropt;
@ -774,7 +779,21 @@ TEST_P(WritePreparedTransactionTest, DoubleSnapshot) {
ASSERT_OK(s);
ASSERT_TRUE(pinnable_val == "value1");
pinnable_val.Reset();
// Cause an eviction to advance max evicted seq number and trigger updating
// the snapshot list
overlap_seq += cache_size;
wp_db->AddCommitted(overlap_seq, overlap_seq);
// It should still see the value before commit
s = wp_db->Get(ropt, wp_db->DefaultColumnFamily(), "key", &pinnable_val);
ASSERT_OK(s);
ASSERT_TRUE(pinnable_val == "value1");
pinnable_val.Reset();
wp_db->ReleaseSnapshot(snapshot0);
wp_db->ReleaseSnapshot(snapshot2);
wp_db->ReleaseSnapshot(snapshot3);
}
// Test that the entries in old_commit_map_ get garbage collected properly

9
utilities/transactions/write_prepared_txn_db.cc
View File

@ -592,8 +592,13 @@ void WritePreparedTxnDB::CleanupReleasedSnapshots(
for (; newi != new_snapshots.end() && oldi != old_snapshots.end();) {
assert(*newi >= *oldi); // cannot have new snapshots with lower seq
if (*newi == *oldi) { // still not released
newi++;
oldi++;
auto value = *newi;
while (newi != new_snapshots.end() && *newi == value) {
newi++;
}
while (oldi != old_snapshots.end() && *oldi == value) {
oldi++;
}
} else {
assert(*newi > *oldi); // *oldi is released
ReleaseSnapshotInternal(*oldi);