rustyrazorblade commented on code in PR #4399:
URL: https://github.com/apache/cassandra/pull/4399#discussion_r2414974162
##########
conf/cassandra.yaml:
##########
@@ -617,6 +617,54 @@ counter_cache_save_period: 7200s
# Disabled by default, meaning all keys are going to be saved
# counter_cache_keys_to_save: 100
+# Dictionary compression settings for ZSTD dictionary-based compression
+# These settings control the automatic training and caching of compression
dictionaries
+# for tables that use ZSTD dictionary compression.
+
+# How often to refresh compression dictionaries across the cluster.
+# During refresh, nodes will check for newer dictionary versions and update
their caches.
+# Min unit: s
+compression_dictionary_refresh_interval: 3600s
+
+# Initial delay before starting the first dictionary refresh cycle after node
startup.
+# This prevents all nodes from refreshing simultaneously when the cluster
starts.
+# Min unit: s
+compression_dictionary_refresh_initial_delay: 10s
+
+# Maximum number of compression dictionaries to cache per table.
+# Each table using dictionary compression can have multiple dictionaries cached
+# (current version plus recently used versions for reading older SSTables).
+compression_dictionary_cache_size: 10
+
+# How long to keep compression dictionaries in the cache before they expire.
+# Expired dictionaries will be removed from memory but can be reloaded if
needed.
+# Min unit: s
+compression_dictionary_cache_expire: 3600s
Review Comment:
I think the eviction code is broken, see my full comment in JIRA. When
compacting a table that I left overnight (assuming the dictionary was evicted)
I get this:
```
WARN [CompactionExecutor:869] 2025-10-08T17:16:05,033
SSTableWriter.java:157 - Failed to open
/Users/jhaddad/dev/cassandra/bin/../data/data/chunk4_2/keyvalue-1b255f4def2540a600000000000000f6/pa-2-big
for writing
java.lang.IllegalStateException: Dictionary is being closed
at
org.apache.cassandra.io.compress.ZstdDictionaryCompressor.lambda$getOrCreate$1(ZstdDictionaryCompressor.java:100)
```
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