cryptoe commented on code in PR #17044:
URL: https://github.com/apache/druid/pull/17044#discussion_r1760473229
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server/src/main/java/org/apache/druid/segment/metadata/FingerprintGenerator.java:
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@@ -53,12 +59,19 @@ public FingerprintGenerator(ObjectMapper objectMapper)
* Generates fingerprint or hash string for an object using SHA-256 hash
algorithm.
*/
@SuppressWarnings("UnstableApiUsage")
- public String generateFingerprint(SchemaPayload schemaPayload, String
dataSource, int version)
+ public String generateFingerprint(final SchemaPayload schemaPayload, final
String dataSource, final int version)
{
+ // Sort the column names in lexicographic order
+ // This ensures that all permutations of a given columns would result in
the same fingerprint
+ // thus avoiding schema explosion in the metadata database
+ // Note that this signature is not persisted anywhere, it is only used for
fingerprint computation
+ final RowSignature sortedSignature =
getLexicographicallySortedSignature(schemaPayload.getRowSignature());
+ final SchemaPayload updatedPayload = new SchemaPayload(sortedSignature,
schemaPayload.getAggregatorFactories());
Review Comment:
Please mention a note about the aggregator factories as well that they are
column order independent since they are backed by a map.
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