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flush cache before segment merge #4955

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merged 6 commits into from
May 23, 2022
Merged

flush cache before segment merge #4955

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2fb0c5b
flush cache before segment merge
lidezhu May 22, 2022
1603fe1
keep flush until success
lidezhu May 22, 2022
9598c4a
check whether segment is valid if flush failed
lidezhu May 22, 2022
ba6be8f
Update dbms/src/Storages/DeltaMerge/tests/gtest_dm_segment.cpp
lidezhu May 22, 2022
d631d4c
add more fix
lidezhu May 22, 2022
4d7de4e
check flush result in segment::write
lidezhu May 23, 2022
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13 changes: 13 additions & 0 deletions dbms/src/Storages/DeltaMerge/DeltaMergeStore.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1971,6 +1971,19 @@ void DeltaMergeStore::segmentMerge(DMContext & dm_context, const SegmentPtr & le
right->info(),
dm_context.min_version);

/// This segment may contain some rows that not belong to this segment range which is left by previous split operation.
/// And only saved data in this segment will be filtered by the segment range in the merge process,
/// unsaved data will be directly copied to the new segment.
/// So we flush here to make sure that all potential data left by previous split operation is saved.
while (!left->flushCache(dm_context))
{
// keep flush until success
}
while (!right->flushCache(dm_context))
{
// keep flush until success
}
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SegmentSnapshotPtr left_snap;
SegmentSnapshotPtr right_snap;
ColumnDefinesPtr schema_snap;
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24 changes: 22 additions & 2 deletions dbms/src/Storages/DeltaMerge/Segment.cpp
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Expand Up @@ -306,7 +306,7 @@ bool Segment::writeToCache(DMContext & dm_context, const Block & block, size_t o
return delta->appendToCache(dm_context, block, offset, limit);
}

bool Segment::write(DMContext & dm_context, const Block & block)
bool Segment::write(DMContext & dm_context, const Block & block, bool flush_cache)
{
LOG_FMT_TRACE(log, "Segment [{}] write to disk rows: {}", segment_id, block.rows());
WriteBatches wbs(dm_context.storage_pool, dm_context.getWriteLimiter());
Expand All @@ -316,7 +316,10 @@ bool Segment::write(DMContext & dm_context, const Block & block)

if (delta->appendColumnFile(dm_context, column_file))
{
flushCache(dm_context);
if (flush_cache)
{
flushCache(dm_context);
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}
return true;
}
else
Expand Down Expand Up @@ -1129,6 +1132,19 @@ SegmentPair Segment::applySplit(DMContext & dm_context, //
SegmentPtr Segment::merge(DMContext & dm_context, const ColumnDefinesPtr & schema_snap, const SegmentPtr & left, const SegmentPtr & right)
{
WriteBatches wbs(dm_context.storage_pool, dm_context.getWriteLimiter());
/// This segment may contain some rows that not belong to this segment range which is left by previous split operation.
/// And only saved data in this segment will be filtered by the segment range in the merge process,
/// unsaved data will be directly copied to the new segment.
/// So we flush here to make sure that all potential data left by previous split operation is saved.
while (!left->flushCache(dm_context))
{
// keep flush until success
}
while (!right->flushCache(dm_context))
{
// keep flush until success
}


auto left_snap = left->createSnapshot(dm_context, true, CurrentMetrics::DT_SnapshotOfSegmentMerge);
auto right_snap = right->createSnapshot(dm_context, true, CurrentMetrics::DT_SnapshotOfSegmentMerge);
Expand All @@ -1149,6 +1165,10 @@ SegmentPtr Segment::merge(DMContext & dm_context, const ColumnDefinesPtr & schem
return merged;
}

/// Segments may contain some rows that not belong to its range which is left by previous split operation.
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/// And only saved data in the segment will be filtered by the segment range in the merge process,
/// unsaved data will be directly copied to the new segment.
/// So remember to do a flush for the segments before merge.
StableValueSpacePtr Segment::prepareMerge(DMContext & dm_context, //
const ColumnDefinesPtr & schema_snap,
const SegmentPtr & left,
Expand Down
3 changes: 2 additions & 1 deletion dbms/src/Storages/DeltaMerge/Segment.h
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Expand Up @@ -144,7 +144,8 @@ class Segment : private boost::noncopyable
bool writeToCache(DMContext & dm_context, const Block & block, size_t offset, size_t limit);

/// For test only.
bool write(DMContext & dm_context, const Block & block);
bool write(DMContext & dm_context, const Block & block, bool flush_cache = true);

bool write(DMContext & dm_context, const RowKeyRange & delete_range);
bool ingestColumnFiles(DMContext & dm_context, const RowKeyRange & range, const ColumnFiles & column_files, bool clear_data_in_range);

Expand Down
28 changes: 19 additions & 9 deletions dbms/src/Storages/DeltaMerge/tests/gtest_dm_segment.cpp
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Expand Up @@ -949,11 +949,17 @@ CATCH
TEST_F(Segment_test, Split)
try
{
const size_t num_rows_write = 100;
const size_t num_rows_write_per_batch = 100;
const size_t num_rows_write = num_rows_write_per_batch * 2;
{
// write to segment
Block block = DMTestEnv::prepareSimpleWriteBlock(0, num_rows_write, false);
segment->write(dmContext(), std::move(block));
// write to segment and flush
Block block = DMTestEnv::prepareSimpleWriteBlock(0, num_rows_write_per_batch, false);
segment->write(dmContext(), std::move(block), true);
}
{
// write to segment and don't flush
Block block = DMTestEnv::prepareSimpleWriteBlock(num_rows_write_per_batch, 2 * num_rows_write_per_batch, false);
segment->write(dmContext(), std::move(block), false);
}

{
Expand Down Expand Up @@ -989,7 +995,7 @@ try
size_t num_rows_seg2 = 0;
{
{
auto in = segment->getInputStream(dmContext(), *tableColumns(), {RowKeyRange::newAll(false, 1)});
auto in = segment->getInputStream(dmContext(), *tableColumns(), {segment->getRowKeyRange()});
in->readPrefix();
while (Block block = in->read())
{
Expand All @@ -998,7 +1004,7 @@ try
in->readSuffix();
}
{
auto in = segment->getInputStream(dmContext(), *tableColumns(), {RowKeyRange::newAll(false, 1)});
auto in = new_segment->getInputStream(dmContext(), *tableColumns(), {new_segment->getRowKeyRange()});
in->readPrefix();
while (Block block = in->read())
{
Expand All @@ -1009,9 +1015,13 @@ try
ASSERT_EQ(num_rows_seg1 + num_rows_seg2, num_rows_write);
}

// delete rows in the right segment
{
new_segment->write(dmContext(), new_segment->getRowKeyRange());
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new_segment->flushCache(dmContext());
}

// merge segments
// TODO: enable merge test!
if (false)
{
segment = Segment::merge(dmContext(), tableColumns(), segment, new_segment);
{
Expand All @@ -1030,7 +1040,7 @@ try
num_rows_read += block.rows();
}
in->readSuffix();
EXPECT_EQ(num_rows_read, num_rows_write);
EXPECT_EQ(num_rows_read, num_rows_seg1);
}
}
}
Expand Down