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https://issues.apache.org/jira/browse/CASSANDRA-21620?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Michael Semb Wever updated CASSANDRA-21620:
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Fix Version/s: 6.0.x
> Stats metadata over-sizes the legacy minimum and maximum clustering values
> --------------------------------------------------------------------------
>
> Key: CASSANDRA-21620
> URL: https://issues.apache.org/jira/browse/CASSANDRA-21620
> Project: Apache Cassandra
> Issue Type: Bug
> Components: Local/SSTable
> Reporter: Michael Semb Wever
> Priority: Normal
> Fix For: 6.0.x, 7.x
>
>
> For an sstable version that still carries the legacy minimum and maximum
> clustering values, {{StatsMetadata.StatsMetadataSerializer.serialize}} writes
> the components of each bound up to the first null one, and writes that count:
> {code:java}
> out.writeInt(countUntilNull(minClusteringValues.getBufferArray()));
> for (ByteBuffer value : minClusteringValues.getBufferArray())
> {
> if (value == null)
> break;
> ByteBufferUtil.writeWithShortLength(value, out);
> }
> {code}
> {{serializedSize}} charges two length bytes for every component the bound
> holds, null ones included:
> {code:java}
> size += minClusteringValues.size() * 2 /* short length */ +
> minClusteringValues.dataSize();
> {code}
> A bound that {{MetadataCollector}} builds holds one entry per clustering
> column, so a covered clustering that stops short of the last column makes the
> two disagree. {{dataSize()}} already counts a null component as zero bytes,
> so the difference is the two length bytes alone.
> {{MetadataSerializer.serialize}} derives the table-of-contents offset of each
> component from the returned size, and writes the whole backing array of a
> buffer allocated to that size. The STATS component therefore ends with two
> unused bytes per absent component. The file stays readable: the reader takes
> the length of each component from the offsets and stops once it has read the
> recorded count.
> No production write reaches the disagreement today, which is why the ticket
> is Low. A writer uses the latest version of its format, where
> {{hasLegacyMinMax()}} is false, and a metadata mutation on an older sstable
> rebuilds the bounds from disk, where they carry exactly the components that
> were written and no nulls. The legacy branch is deprecated and due for
> removal after {{oa}}; until then the two halves of the serializer must agree,
> because the offset arithmetic depends on it.
> The patch sizes both bounds with {{countUntilNull}}, the same count the
> writer uses.
> Patch:
> [mck/CASSANDRA-21620/trunk|https://github.com/thelastpickle/cassandra/tree/mck/CASSANDRA-21620/trunk]
> Provenance:
> [f57af096a0|https://github.com/datastax/cassandra/commit/f57af096a0a9b5225d46dc860ab683d26156a013]
> by Jacek Lewandowski. That commit repairs the size computation only; the
> writer already counts to the first null upstream.
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