Add a feature flag for disabling erase cache

Author: snaury

ydb/core/protos/feature_flags.proto

@@ -183,4 +183,5 @@ message TFeatureFlags {
     optional bool EnableVDiskThrottling = 158 [default = false];
     optional bool EnableDataShardInMemoryStateMigration = 159 [default = true];
     optional bool EnableDataShardInMemoryStateMigrationAcrossGenerations = 160 [default = false];
+    optional bool DisableLocalDBEraseCache = 161 [default = false];
 }

ydb/core/tx/datashard/datashard_user_table.cpp

@@ -484,7 +484,9 @@ void TUserTable::DoApplyCreate(
             alter.SetExecutorFastLogPolicy(partConfig.GetExecutorFastLogPolicy());
         }
 
-        alter.SetEraseCache(tid, partConfig.GetEnableEraseCache(), partConfig.GetEraseCacheMinRows(), partConfig.GetEraseCacheMaxBytes());
+        if (!AppData().FeatureFlags.GetDisableEraseCache()) {
+            alter.SetEraseCache(tid, partConfig.GetEnableEraseCache(), partConfig.GetEraseCacheMinRows(), partConfig.GetEraseCacheMaxBytes());
+        }
 
         if (IsBackup) {
             alter.SetColdBorrow(tid, true);
@@ -630,7 +632,9 @@ void TUserTable::ApplyAlter(
         if (configDelta.HasEraseCacheMaxBytes()) {
             config.SetEraseCacheMaxBytes(configDelta.GetEraseCacheMaxBytes());
         }
-        alter.SetEraseCache(LocalTid, config.GetEnableEraseCache(), config.GetEraseCacheMinRows(), config.GetEraseCacheMaxBytes());
+        if (!AppData().FeatureFlags.GetDisableEraseCache()) {
+            alter.SetEraseCache(LocalTid, config.GetEnableEraseCache(), config.GetEraseCacheMinRows(), config.GetEraseCacheMaxBytes());
+        }
     }
 
     schema.SetTableSchemaVersion(delta.GetTableSchemaVersion());
@@ -650,12 +654,19 @@ void TUserTable::ApplyDefaults(TTransactionContext& txc) const
     GetSchema(schema);
     const auto& config = schema.GetPartitionConfig();
 
-    if ((!config.HasEnableEraseCache() && config.GetEnableEraseCache() != tableInfo->EraseCacheEnabled) ||
-        (config.GetEnableEraseCache() && !config.HasEraseCacheMinRows() && config.GetEraseCacheMinRows() != tableInfo->EraseCacheMinRows) ||
-        (config.GetEnableEraseCache() && !config.HasEraseCacheMaxBytes() && config.GetEraseCacheMaxBytes() != tableInfo->EraseCacheMaxBytes))
-    {
-        // Protobuf defaults for erase cache changed, apply to local database
-        txc.DB.Alter().SetEraseCache(LocalTid, config.GetEnableEraseCache(), config.GetEraseCacheMinRows(), config.GetEraseCacheMaxBytes());
+    if (AppData().FeatureFlags.GetDisableEraseCache()) {
+        // Erase cache was disabled, make sure it is disabled in the schema as well
+        if (tableInfo->EraseCacheEnabled) {
+            txc.DB.Alter().SetEraseCache(LocalTid, false, 0, 0);
+        }
+    } else {
+        // Erase cache not disabled, make sure current settings are re-applied
+        if ((config.GetEnableEraseCache() != tableInfo->EraseCacheEnabled) ||
+            (config.GetEnableEraseCache() && config.GetEraseCacheMinRows() != tableInfo->EraseCacheMinRows) ||
+            (config.GetEnableEraseCache() && config.GetEraseCacheMaxBytes() != tableInfo->EraseCacheMaxBytes))
+        {
+            txc.DB.Alter().SetEraseCache(LocalTid, config.GetEnableEraseCache(), config.GetEraseCacheMinRows(), config.GetEraseCacheMaxBytes());
+        }
     }
 }