# Error: Replication backlog buffer overflow, disconnecting replica

- **ID:** `redis/replica-repl-backlog-overflow`
- **Domain:** redis
- **Category:** system_error
- **Error Code:** `ERM`
- **Verification:** ai_generated
- **Fix Rate:** 85%

## Root Cause

The replication backlog buffer on the primary node exceeded its configured size, causing the node to disconnect replicas to prevent memory exhaustion.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| Redis 6.2.6 | active | — | — |
| Redis 7.0.12 | active | — | — |
| Redis 7.2.4 | active | — | — |

## Workarounds

1. **Increase the replication backlog size: CONFIG SET repl-backlog-size 100mb. This provides more buffer for replicas to catch up.** (90% success)
   ```
   Increase the replication backlog size: CONFIG SET repl-backlog-size 100mb. This provides more buffer for replicas to catch up.
   ```
2. **Add more replicas or improve network bandwidth to reduce replication lag. Monitor with INFO replication.** (80% success)
   ```
   Add more replicas or improve network bandwidth to reduce replication lag. Monitor with INFO replication.
   ```
3. **Enable client output buffer limits for replicas: CONFIG SET client-output-buffer-limit replica 256mb 64mb 60. This prevents a single slow replica from overwhelming the backlog.** (85% success)
   ```
   Enable client output buffer limits for replicas: CONFIG SET client-output-buffer-limit replica 256mb 64mb 60. This prevents a single slow replica from overwhelming the backlog.
   ```

## Dead Ends

- **** — Setting backlog size to zero disables partial resynchronization, forcing full syncs on each reconnect, increasing network load. (80% fail)
- **** — Restarting clears the backlog temporarily but does not address the root cause of high write volume or slow replicas. (75% fail)
- **** — Large keys are not the direct cause; the backlog overflow is due to accumulated write commands, not key size. (50% fail)