apache/druid · error · ExpressionProcessingException

failed to deserialize bloom filter

Error message

failed to deserialize bloom filter

What it means

When deserializing a base64-encoded BloomKFilter from bytes, an IOException causes the expression code to fail with 'failed to deserialize bloom filter'. This means the serialized filter bytes are corrupt, truncated, or not a valid BloomKFilter format.

Solutions

1. Regenerate the base64 filter string with base64_to/from using the same Druid version that will consume it.
2. Verify the base64 string is complete and has no whitespace or truncation.
3. Confirm the filter was produced as a BloomKFilter (not another bloom implementation) via bloom_filter_expr.

Example fix

// before
WHERE filter_bloom(x, 'SGVsbG8')  -- truncated base64
// after
WHERE filter_bloom(x, '<full base64 of bloom_filter_expr output>')

// sanity-check base64 length before use
byte[] decoded = java.util.Base64.getDecoder().decode(b64.trim());
if (decoded.length < 16) throw new IllegalArgumentException("bloom filter base64 too short/corrupt");

try { filter_bloom(x, b64Filter); } catch (ExpressionProcessingException e) { /* regenerate filter via bloom_filter_expr and retry */ }

When it happens

Trigger: Applying a literal bloom filter expression where the base64 string decodes to bytes that BloomFilterSerializersModule.bloomKFilterFromBytes cannot parse.

Common situations: Manually constructed/truncated base64 strings; filters serialized by an incompatible Druid version; whitespace or corruption introduced when copying the base64 string; passing a bloom_filter_expr output where a K-filter format is required.

Understand the failure class

Background: "failed to unmarshal" / json.Unmarshal errors: why parsing a response into a Go struct fails and how to fix it — this error's family across 23 libraries.

Related errors

• Failed to deserialize bloom filter
• Failed to deserialize to RoaringBitmap64Counter, input is…
• Input stream is null
• interrupted flushing elements from queue
• unknown event type [ ]

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/46f63f1fbe807356. Report an issue: GitHub.

Appendix: source

Thrown at extensions-core/druid-bloom-filter/src/main/java/org/apache/druid/query/expressions/BloomFilterExpressions.java:328

        }

        @Nullable
        @Override
        public ExpressionType getOutputType(InputBindingInspector inspector)
        {
          return ExpressionType.LONG;
        }
      }

      if (filterExpr.isLiteral() && filterExpr.getLiteralValue() instanceof String) {
        final String serializedFilter = (String) filterExpr.getLiteralValue();
        final byte[] decoded = StringUtils.decodeBase64String(serializedFilter);
        BloomKFilter filter;
        try {
          filter = BloomFilterSerializersModule.bloomKFilterFromBytes(decoded);
        }
        catch (IOException ioe) {
          throw processingFailed(ioe, "failed to deserialize bloom filter");
        }
        return new BloomExpr(filter, args);
      } else {
        return new DynamicBloomExpr(args);
      }
    }
  }
}

View on GitHub (pinned to 9b90983fd2)