introduce some artificial delays in the eviction script

...and reduce the margin of error in its bloom filters

lib/eviction.js

@@ -81,7 +81,9 @@ module.exports = function (Env, cb) {
         TODO make this configurable ?
     */
     var BLOOM_CAPACITY = (1 << 20) - 1; // over a million items
-    var BLOOM_ERROR = 1 / 1000;  // an error rate of one in a thousand
+    var BLOOM_ERROR = 1 / 10000;  // an error rate of one in a thousand
+    // the number of ms artificially introduced between CPU-intensive operations
+    var THROTTLE_FACTOR = 10;
 
     // we'll use one filter for the set of active documents
     var activeDocs = Bloom.optimalFilter(BLOOM_CAPACITY, BLOOM_ERROR);
@@ -165,6 +167,7 @@ module.exports = function (Env, cb) {
     // if they are older than the specified retention time
         var removed = 0;
         blobs.list.archived.proofs(function (err, item, next) {
+            next = Util.mkAsync(next, THROTTLE_FACTOR);
             if (err) {
                 Log.error("EVICT_BLOB_LIST_ARCHIVED_PROOF_ERROR", err);
                 return void next();
@@ -190,6 +193,7 @@ module.exports = function (Env, cb) {
     // if they are older than the specified retention time
         var removed = 0;
         blobs.list.archived.blobs(function (err, item, next) {
+            next = Util.mkAsync(next, THROTTLE_FACTOR);
             if (err) {
                 Log.error("EVICT_BLOB_LIST_ARCHIVED_BLOBS_ERROR", err);
                 return void next();
@@ -246,6 +250,7 @@ module.exports = function (Env, cb) {
         var active = 0;
 
         blobs.list.blobs(function (err, item, next) {
+            next = Util.mkAsync(next, THROTTLE_FACTOR);
             n_blobs++;
             if (err) {
                 Log.error("EVICT_BLOB_CATEGORIZATION", err);
@@ -311,6 +316,7 @@ module.exports = function (Env, cb) {
         // otherwise, we'll only retain data from active accounts
         // so we need more heuristics
         var handler = function (content, id, next) {
+            next = Util.mkAsync(next, THROTTLE_FACTOR);
             accounts++;
 
             var mtime = content.latest;
@@ -416,6 +422,7 @@ module.exports = function (Env, cb) {
     // if they don't correspond to a pinned or active file
         var removed = 0;
         blobs.list.proofs(function (err, item, next) {
+            next = Util.mkAsync(next, THROTTLE_FACTOR);
             if (err) {
                 next();
                 return void Log.error("EVICT_BLOB_LIST_PROOFS_ERROR", err);
@@ -458,6 +465,7 @@ module.exports = function (Env, cb) {
         var archived = 0;
 
         var handler = function (err, item, cb) {
+            cb = Util.mkAsync(cb, THROTTLE_FACTOR);
             channels++;
             if (err) {
                 Log.error('EVICT_CHANNEL_ITERATION', err);