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This commit is contained in:
Jaifroid 2020-11-04 21:33:23 +00:00
parent dc03760cef
commit e73ff106ab
1 changed files with 24 additions and 15 deletions
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39
www/js/lib/filecache.js
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@ -50,7 +50,8 @@ define(['q'], function(Q) {
* LRUCache implemnentation with Map adapted from https://markmurray.co/blog/lru-cache/ * LRUCache implemnentation with Map adapted from https://markmurray.co/blog/lru-cache/
*/ */
function LRUCache() { function LRUCache() {
console.log('Creating cache of size ' + MAX_CACHE_SIZE + ' * ' + BLOCK_SIZE + ' bytes'); /** CACHE TUNING **/
// console.log('Creating cache of size ' + MAX_CACHE_SIZE + ' * ' + BLOCK_SIZE + ' bytes');
// Initialize persistent Cache properties // Initialize persistent Cache properties
this.capacity = MAX_CACHE_SIZE; this.capacity = MAX_CACHE_SIZE;
this.cache = new Map(); this.cache = new Map();
@ -79,12 +80,14 @@ define(['q'], function(Q) {
* @param {Uint8Array} value The value to store in the cache * @param {Uint8Array} value The value to store in the cache
*/ */
LRUCache.prototype.store = function (key, value) { LRUCache.prototype.store = function (key, value) {
// We get the existing entry's object for memory-management purposes; if it exists, it will contain identical data
// to <value>, but <entry> is strongly referenced by the Map. (It should be rare that two async Promises attempt to
// store the same data in the Cache, once the Cache is sufficiently populated.)
var entry = this.cache.get(key); var entry = this.cache.get(key);
// If the key already exists, delete it so that it will be added // If the key already exists, delete it and re-insert it, so that it will be added
// to the bottom of the Map (bottom = most recent) // to the bottom of the Map (bottom = most recent)
if (entry) this.cache.delete(key); if (entry) this.cache.delete(key);
else entry = value; else entry = value;
// Store a reference to the entry in the Map
this.cache.set(key, entry); this.cache.set(key, entry);
// If we've exceeded the cache capacity, then delete the least recently accessed value, // If we've exceeded the cache capacity, then delete the least recently accessed value,
// which will be the item at the top of the Map, i.e the first position // which will be the item at the top of the Map, i.e the first position
@ -93,11 +96,11 @@ define(['q'], function(Q) {
var firstKey = this.cache.keys().next().value; var firstKey = this.cache.keys().next().value;
this.cache.delete(firstKey); this.cache.delete(firstKey);
} else { } else {
// IE11 doesn't support the keys iterator, so we have to do forEach loop through all 4000 entries // IE11 doesn't support the keys iterator, so we have to do a forEach loop through all 4000 entries
// to get the oldest values. To prevent excessive iterations, we delete 25% at a time. // to get the oldest values. To prevent excessive iterations, we delete 25% at a time.
var q = Math.floor(0.25 * this.capacity); var q = Math.floor(0.25 * this.capacity);
var c = 0; var c = 0;
console.log('Deleteing ' + q + ' cache entries'); // console.log('Deleteing ' + q + ' cache entries');
this.cache.forEach(function (v, k, map) { this.cache.forEach(function (v, k, map) {
if (c > q) return; if (c > q) return;
map.delete(k); map.delete(k);
@ -113,9 +116,11 @@ define(['q'], function(Q) {
*/ */
var cache = new LRUCache(); var cache = new LRUCache();
// Counters for reporting only /** CACHE TUNING **/
var hits = 0;
var misses = 0; // DEV: Uncomment this block and blocks below marked 'CACHE TUNING' to measure Cache hit and miss rates for different Cache sizes
// var hits = 0;
// var misses = 0;
/** /**
* Read a certain byte range in the given file, breaking the range into chunks that go through the cache * Read a certain byte range in the given file, breaking the range into chunks that go through the cache
@ -137,7 +142,8 @@ define(['q'], function(Q) {
var block = cache.get(file.id + ':' + id); var block = cache.get(file.id + ':' + id);
if (block === undefined) { if (block === undefined) {
// Data not in cache, so read from archive // Data not in cache, so read from archive
misses++; /** CACHE TUNING **/
// misses++;
// DEV: This is a self-calling function, i.e. the function is called with an argument of <id> which then // DEV: This is a self-calling function, i.e. the function is called with an argument of <id> which then
// becomes the <offset> parameter // becomes the <offset> parameter
readRequests.push(function(offset) { readRequests.push(function(offset) {
@ -147,15 +153,18 @@ define(['q'], function(Q) {
}); });
}(id)); }(id));
} else { } else {
hits++; /** CACHE TUNING **/
// hits++;
blocks[id] = block; blocks[id] = block;
} }
} }
if (misses + hits > 2000) { /** CACHE TUNING **/
console.log("** Block cache hit rate: " + Math.round(hits / (hits + misses) * 1000) / 10 + "% [ hits:" + hits + " / misses:" + misses + " ]"); // if (misses + hits > 2000) {
hits = 0; // console.log('** Block cache hit rate: ' + Math.round(hits / (hits + misses) * 1000) / 10 + '% [ hits:' + hits +
misses = 0; // ' / misses:' + misses + ' ] Size: ' + cache.cache.size);
} // hits = 0;
// misses = 0;
// }
// Wait for all the blocks to be read either from the cache or from the archive // Wait for all the blocks to be read either from the cache or from the archive
return Q.all(readRequests).then(function() { return Q.all(readRequests).then(function() {
var result = new Uint8Array(end - begin); var result = new Uint8Array(end - begin);