Xiao Liu created HBASE-30246:
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Summary: MOB compaction does not close MobCell after resolving
reference cells
Key: HBASE-30246
URL: https://issues.apache.org/jira/browse/HBASE-30246
Project: HBase
Issue Type: Bug
Components: Compaction, mob
Reporter: Xiao Liu
Assignee: Xiao Liu
Fix For: 2.7.0, 3.0.0-beta-2, 2.5.16, 2.6.7
During MOB compaction, \{{DefaultMobStoreCompactor}} resolves each MOB
reference cell via:
{code:java}
mobCell = mobStore.resolve(c, cacheMobBlocksOnCompaction, false).getCell();
{code}
{\{HMobStore#resolve(...)}} returns a \{{Closeable}} \{{MobCell}} that owns the
{\{StoreFileScanner}} opened against the MOB file (and the off-heap ByteBuffers
backing
the cell). The code calls \{{getCell()}} and drops the \{{MobCell}}, so the
scanner/buffers
are never released — once per reference cell, for the whole compaction. On the
off-heap
read path this pressures the \{{ByteBuffAllocator}} pool and can lead to buffer
exhaustion
during large MOB compactions. The bug is long-standing (it predates
HBASE-30177, which only
changed the cacheBlocks argument) and was spotted during the HBASE-30177 review.
h3. Fix
Close the \{{MobCell}} via try-with-resources right after resolving. The cell
must be copied
to the heap *before* close, because closing releases/recycles the buffers
backing it, while
HFile writers/encoders retain references to appended cells (lastCell,
firstCellInBlock,
encoder prevCell) until \{{beforeShipped()}}. Closing without copying would
turn the leak into
silent HFile corruption.
{code:java}
protected ExtendedCell resolveMobCell(ExtendedCell reference) throws
IOException {
try (MobCell mobCell = mobStore.resolve(reference, cacheMobBlocksOnCompaction,
false)) {
return KeyValueUtil.copyToNewKeyValue(mobCell.getCell());
}
}
{code}
h3. Testing
* New
\{{TestDefaultMobStoreCompactor#testResolveMobCellClosesMobCellAndReturnsIndependentCopy}}
asserts \{{close()}} is called and an independent heap copy is returned.
* \{{TestHMobStore}} updated to close resolved \{{MobCell}}s.
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