trim lookup tables for channels without checkpoints

lib/workers/db-worker.js

@@ -118,6 +118,7 @@ const computeIndex = function (data, cb) {
     const CB = Util.once(cb);
 
     const offsetByHash = {};
+    let offsetCount = 0;
     let size = 0;
     nThen(function (w) {
         // iterate over all messages in the channel log
@@ -151,6 +152,8 @@ const computeIndex = function (data, cb) {
                     // so clear the buffer every time you see a new one
                     messageBuf = [];
                 }
+            } else if (messageBuf.length > 100 && cpIndex.length === 0) {
+                messageBuf = messageBuf.slice(0, 50);
             }
             // if it's not metadata or a checkpoint then it should be a regular message
             // store it in the buffer
@@ -163,6 +166,7 @@ const computeIndex = function (data, cb) {
             }
 
             // once indexing is complete you should have a buffer of messages since the latest checkpoint
+            // or the 50-100 latest messages if the channel is of a type without checkpoints.
             // map the 'hash' of each message to its byte offset in the log, to be used for reconnecting clients
             messageBuf.forEach((msgObj) => {
                 const msg = HK.tryParse(Env, msgObj.buff.toString('utf8'));
@@ -171,6 +175,7 @@ const computeIndex = function (data, cb) {
                     // msgObj.offset is API guaranteed by our storage module
                     // it should always be a valid positive integer
                     offsetByHash[HK.getHash(msg[4])] = msgObj.offset;
+                    offsetCount++;
                 }
                 // There is a trailing \n at the end of the file
                 size = msgObj.offset + msgObj.buff.length + 1;
@@ -182,6 +187,7 @@ const computeIndex = function (data, cb) {
             // Only keep the checkpoints included in the last 100 messages
             cpIndex: HK.sliceCpIndex(cpIndex, i),
             offsetByHash: offsetByHash,
+            offsets: offsetCount,
             size: size,
             //metadata: metadata,
             line: i