apache/cassandra · error · IOException

Failed to save index summary to

Error message

Failed to save index summary to 

What it means

Thrown when writing an index summary to Summary.db fails with an IOException; if deleteOnFailure was set the partial file is removed first. This indicates the SSTable could not persist its summary, preventing it from being opened.

Source

Thrown at src/java/org/apache/cassandra/io/sstable/format/big/IndexSummaryComponent.java:133

    /**
     * Save index summary to Summary.db file.
     */
    public void save(File summaryFile, boolean deleteOnFailure) throws IOException
    {
        if (summaryFile.exists())
            summaryFile.delete();

        try (DataOutputStreamPlus oStream = summaryFile.newOutputStream(File.WriteMode.OVERWRITE))
        {
            IndexSummary.serializer.serialize(indexSummary, oStream);
            ByteBufferUtil.writeWithLength(first.getKey(), oStream);
            ByteBufferUtil.writeWithLength(last.getKey(), oStream);
        }
        catch (IOException ex)
        {
            if (deleteOnFailure)
                summaryFile.deleteIfExists();
            throw new IOException("Failed to save index summary to " + summaryFile, ex);
        }
    }
}

View on GitHub (pinned to 88fd0f6a0e)

Solutions

1. Free disk space on the data directory and retry the operation/restart
2. Fix directory permissions/ownership so Cassandra can write Summary.db
3. Check filesystem health; remove leftover partial Summary.db files (already deleted when deleteOnFailure) and reopen

// Pre-flight checks before opening SSTables
assert dataDir.canWrite() : "data dir not writable";
assert dataDir.getUsableSpace() > minRequiredBytes : "insufficient disk space";

try { sstable = openComponents(...); }
catch (IOException e) {
    logger.error("Failed saving index summary to {}: {}", e.getMessage(), e.getCause());
    alertDiskOrPermissions();
}

When it happens

Trigger: Opening an SSTable that requires building/saving its index summary (e.g. summary rebuild on open via openComponents) and the write fails — disk full, permission denied, or I/O error on the SSTable directory.

Common situations: Disk full on the data volume; read-only or wrong-ownership data directory; filesystem errors; interrupted save.

Understand the failure class

Background: "failed to write file", "Could not save figure", "Error saving remote file" — file write failed: causes and fixes across languages and libraries — this error's family across 38 libraries.

Related errors

• SyncException (wraps IOException from disk writer flush/sync
• FSWriteError (wraps IOException writing sstable component)
• Failed to save Bloom filter for SSTable:
• Corrupt flags value for clustering prefix (isStatic flag set
• Corrupted sstable. Invalid flags found deserializing Deletio

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/26ec5b53af7b813a. Report an issue: GitHub.