guluo2016 commented on code in PR #8392:
URL: https://github.com/apache/hbase/pull/8392#discussion_r3466262715
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hbase-server/src/main/java/org/apache/hadoop/hbase/mob/DefaultMobStoreCompactor.java:
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@@ -174,6 +175,29 @@ public DefaultMobStoreCompactor(Configuration conf, HStore
store) {
MobConstants.DEFAULT_MOB_COMPACTION_READ_CACHE_BLOCKS);
}
+ /**
+ * Resolves a MOB reference cell to its backing MOB value and returns an
independent,
+ * heap-resident copy of the resolved cell.
+ * <p>
+ * A MOB cell resolved from a MOB file is backed by a {@code
StoreFileScanner}; closing the
+ * {@link MobCell} closes that scanner and may release/recycle the NIO
buffers referenced by the
+ * returned cell. We close the {@link MobCell} here to avoid leaking
scanners/buffers while
+ * compacting many reference cells.
+ * <p>
+ * The {@link KeyValueUtil#copyToNewKeyValue(ExtendedCell)} call is required
by this ownership
+ * model: HFile writers and encoders may retain references to appended cells
(e.g.
+ * {@code lastCell}, {@code firstCellInBlock}, and the data block encoder's
{@code prevCell})
+ * until {@code beforeShipped()}. Returning the scanner-backed cell directly
would let those later
+ * reads access released buffers. Removing this copy would require changing
the caller to retain
+ * each {@link MobCell} and close it only after the writers have shipped
their retained
+ * references.
+ */
+ protected ExtendedCell resolveMobCell(ExtendedCell reference) throws
IOException {
+ try (MobCell mobCell = mobStore.resolve(reference,
cacheMobBlocksOnCompaction, false)) {
Review Comment:
Agreed, thanks.
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