Error 49: LOGICAL_ERROR

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This error indicates an internal bug or assertion failure in ClickHouse that should not occur under normal circumstances. It represents a violation of internal invariants or unexpected conditions that point to a bug in ClickHouse itself rather than a user error.

Most common causes

1. Internal assertion failures

   • Failed internal consistency checks
   • Invariant violations in ClickHouse code
   • Unexpected state transitions that should never happen
   • Buffer or pointer validation failures

2. File system cache issues

   • Inconsistent cache state in S3 or remote filesystem operations
   • Buffer offset mismatches (e.g., "Expected X >= Y")
   • File segment inconsistencies

3. Merge tree operations

   • Part management issues (e.g., "Entry actual part isn't empty yet")
   • Temporary part conflicts
   • Part state inconsistencies during merges or mutations

4. Query optimizer or planner bugs

   • Incorrect operand types in expressions
   • Invalid query plan generation
   • Column type mismatches in internal processing

5. Concurrency and synchronization issues

   • Race conditions in multi-threaded operations
   • Lock ordering violations
   • State corruption from concurrent access

6. LLVM compilation errors

   • Incorrect operand types in compiled expressions
   • JIT compilation failures

What to do when you encounter this error

1. This is a bug - report it to ClickHouse

LOGICAL_ERROR always indicates a bug in ClickHouse, not a user error. The error message typically says "Report this error to https://github.com/ClickHouse/ClickHouse/issues"

2. Gather diagnostic information

Before reporting, collect:

-- Get the full error message and stack trace from logs
SELECT 
    event_time,
    query_id,
    exception,
    exception_code,
    stack_trace
FROM system.query_log
WHERE exception_code = 49
ORDER BY event_time DESC
LIMIT 10;

3. Note your ClickHouse version

SELECT version();

4. Try to create a minimal reproducible example

If possible, identify:

• The specific query that triggers the error
• Table schema and sample data
• Any recent operations (merges, mutations, ALTER statements)

5. Check if the issue is already fixed

Search existing issues on GitHub Consider upgrading to a newer version if available.

Temporary workarounds

While waiting for a fix, you may try:

1. Restart the server or retry the operation

# Sometimes temporary state corruption can be cleared
sudo systemctl restart clickhouse-server

2. Optimize or rebuild affected parts

-- For specific table issues
OPTIMIZE TABLE your_table FINAL;

-- Or detach and reattach the table
DETACH TABLE your_table;
ATTACH TABLE your_table;

3. Disable experimental features

-- If using experimental features, try disabling them
SET allow_experimental_analyzer = 0;
SET compile_expressions = 0;

4. Adjust settings that may trigger the bug

-- For filesystem cache issues
SET enable_filesystem_cache = 0;

-- For query optimization issues
SET query_plan_enable_optimizations = 0;

5. Use alternative query formulation

If a specific query pattern triggers the error, try rewriting the query differently.

Common specific scenarios

Scenario 1: Buffer offset mismatch

Logical error: 'Expected 46044 >= 88088'

This typically occurs with S3 or remote filesystem cache. Try:

• Clearing the filesystem cache
• Disabling cache temporarily
• Upgrading to a newer version

Scenario 2: Part management errors

Logical error: 'Entry actual part isn't empty yet'

Related to merge tree part operations. Try:

• OPTIMIZE TABLE FINAL
• Checking for stuck merges in system.merges
• Checking mutations in system.mutations

Scenario 3: LLVM compilation errors

Logical error: Incorrect operand type

Related to expression compilation. Try:

SET compile_expressions = 0;
SET compile_aggregate_expressions = 0;