[BUG] maxmemory eviction fails under large dataset, memory usage exceeds maxmemory and keeps growing until OOM

Describe the bug

We are seeing a problem with KeyDB 6.3.4 where memory eviction does not work correctly under a large dataset.

When the dataset grows to around 1.7 million keys and disk usage reaches about 300 GB, the server continuously reports:

Failed to evict keys, falling back to flushing entire cache. Consider increasing maxmemory-samples.

We already increased maxmemory-samples from 16 to 256, but the error still continues.

At the same time, the instance memory usage goes beyond the configured maxmemory limit (44 GB), and memory usage keeps increasing until the whole server memory is exhausted, eventually causing OOM / service failure.

This makes it look like eviction is not functioning as expected when flash storage is enabled and the dataset becomes large.

Observed behavior

Dataset grows to about 1.7 million keys Disk usage grows to about 300 GB KeyDB repeatedly logs: Failed to evict keys, falling back to flushing entire cache. Consider increasing maxmemory-samples. Increasing maxmemory-samples from 16 to 256 does not solve the issue Actual memory usage exceeds maxmemory 44gb Memory continues to grow instead of being controlled by eviction Eventually the server runs out of memory

Expected behavior

When memory usage reaches maxmemory, KeyDB should evict keys according to allkeys-lru and keep memory usage under control.

It should not continue growing beyond the configured memory limit until the server OOMs.

Additional information Environment KeyDB version: 6.3.4 OS: Ubuntu 22.04 Server spec: 8 CPU, 64 GB RAM Disk: SSD 500 GB

Configuration bind 0.0.0.0 port 6379 protected-mode yes

tcp-backlog 8192

timeout 0 tcp-keepalive 300

daemonize yes pidfile /var/run/keydb/keydb-server.pid supervised no loglevel notice logfile /var/log/keydb/keydb-server.log

databases 16 maxclients 10000

server-threads 4

maxmemory 44gb maxmemory-policy allkeys-lru maxmemory-samples 256

Flash

storage-provider flash /opt/data1/keydb/flash dir /opt/data1/keydb

save "" stop-writes-on-bgsave-error no rdbcompression yes rdbchecksum yes

lazyfree-lazy-eviction yes lazyfree-lazy-expire yes lazyfree-lazy-server-del yes

slowlog-log-slower-than 10000 slowlog-max-len 1024 latency-monitor-threshold 100