Bharatendra Boddu created CASSANDRA-9792:
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Summary: Reduce Merkle tree serialized size
Key: CASSANDRA-9792
URL: https://issues.apache.org/jira/browse/CASSANDRA-9792
Project: Cassandra
Issue Type: Improvement
Components: Core
Reporter: Bharatendra Boddu
Priority: Minor
Attachments: MerkleTree.java.patch
This patch reduces the serialized size of a Merkle Tree by 10%. With
num_tokens set to 256, 10% reduction in Merkle tree serialized size for each
token range repair, improves network bandwidth during repair
This table describes serialized sizes (in bytes) of Merkle trees with different
depths before and after patch.
Serialized size of a Merkle tree with certain depth, doesn't depend on number
of keys it represent.
| Depth | Before patch | After patch | Diff |
|-------+--------------+-------------+-------|
| 5 | 2060 | 1840 | 220 |
| 6 | 4044 | 3600 | 444 |
| 7 | 8012 | 7120 | 892 |
| 8 | 15948 | 14160 | 1788 |
| 9 | 31820 | 28240 | 3580 |
| 10 | 63564 | 56400 | 7164 |
| 11 | 127052 | 112720 | 14332 |
| 12 | 254028 | 225360 | 28668 |
| 13 | 507980 | 450640 | 57340 |
Merkle tree with depth 15, uses serialized size of ~2MB and with this patch it
will be reduce the size by ~200KB. Repairing 256 token ranges will save ~50MB
in transfer.
Also if token serialize() method uses, byte type to represent a token size,
then the serialized size can be reduced by 30 to 40%.
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