Memory-based pruning history size (#4114)

* prune states based on memory param

* pruning memory CLI and usage in sync

* return purged value from memorydb

* calculate memory used incrementally in overlayrecentdb

* refactor shared history pruning code in client

* Fixed usage alignment

* journal_size function for fast memory calculation

parity/cli/config.full.toml

@@ -95,6 +95,7 @@ notify_work = ["http://localhost:3001"]
 tracing = "auto"
 pruning = "auto"
 pruning_history = 1200
+pruning_memory = 500
 cache_size_db = 64
 cache_size_blocks = 8
 cache_size_queue = 50

parity/cli/mod.rs

@@ -238,6 +238,8 @@ usage! {
 			or |c: &Config| otry!(c.footprint).pruning.clone(),
 		flag_pruning_history: u64 = 1200u64,
 			or |c: &Config| otry!(c.footprint).pruning_history.clone(),
+		flag_pruning_memory: usize = 150usize,
+			or |c: &Config| otry!(c.footprint).pruning_memory.clone(),
 		flag_cache_size_db: u32 = 64u32,
 			or |c: &Config| otry!(c.footprint).cache_size_db.clone(),
 		flag_cache_size_blocks: u32 = 8u32,
@@ -421,6 +423,7 @@ struct Footprint {
 	tracing: Option<String>,
 	pruning: Option<String>,
 	pruning_history: Option<u64>,
+	pruning_memory: Option<usize>,
 	fast_and_loose: Option<bool>,
 	cache_size: Option<u32>,
 	cache_size_db: Option<u32>,
@@ -635,6 +638,7 @@ mod tests {
 			flag_tracing: "auto".into(),
 			flag_pruning: "auto".into(),
 			flag_pruning_history: 1200u64,
+			flag_pruning_memory: 500usize,
 			flag_cache_size_db: 64u32,
 			flag_cache_size_blocks: 8u32,
 			flag_cache_size_queue: 50u32,
@@ -812,6 +816,7 @@ mod tests {
 				tracing: Some("on".into()),
 				pruning: Some("fast".into()),
 				pruning_history: Some(64),
+				pruning_memory: None,
 				fast_and_loose: None,
 				cache_size: None,
 				cache_size_db: Some(128),

parity/cli/usage.txt

@@ -271,8 +271,12 @@ Footprint Options:
                            fast - maintain journal overlay. Fast but 50MB used.
                            auto - use the method most recently synced or
                            default to fast if none synced (default: {flag_pruning}).
-  --pruning-history NUM    Set a number of recent states to keep when pruning
+  --pruning-history NUM    Set a minimum number of recent states to keep when pruning
                            is active. (default: {flag_pruning_history}).
+  --pruning-memory MB      The ideal amount of memory in megabytes to use to store
+                           recent states. As many states as possible will be kept
+                           within this limit, and at least --pruning-history states
+                           will always be kept. (default: {flag_pruning_memory})
   --cache-size-db MB       Override database cache size (default: {flag_cache_size_db}).
   --cache-size-blocks MB   Specify the prefered size of the blockchain cache in
                            megabytes (default: {flag_cache_size_blocks}).