diff --git a/scripts/build-raw-near-lake-index.js b/scripts/build-raw-near-lake-index.js
index 2c2d14a..48b20da 100644
--- a/scripts/build-raw-near-lake-index.js
+++ b/scripts/build-raw-near-lake-index.js
@@ -1,7 +1,6 @@
 
-const compressing = require('compressing');
-
 const fs = require('fs');
+const { writeFile } = require('fs/promises');
 const zlib = require('zlib');
 const tar = require('tar-stream');
 
@@ -16,18 +15,29 @@ async function main() {
     const dstDir = `./lake-data/${bucketName}`;
     // TODO: Make shards dynamic, allow to filter by shard
     // TODO: Should index smth from 'block' as well? (e.g. block.header.timestamp)
-    const folders = ['0', '1', '2', '3'];
+    const shards = ['0', '1', '2', '3'];
+
+    for (let shard of shards) {
+        console.log('Processing shard', shard);
+
+        const unmerged = [];
+        for await (const changesByAccount of changesByAccountStream(shard, startBlockNumber, endBlockNumber)) {
+            unmerged.push(changesByAccount);
+        }
 
-    for (let folder of folders) {
-        console.log('Processing shard', folder);
+        const allChangesByAccount = mergeChangesByAccount(unmerged);
+        // console.log('allChangesByAccount', allChangesByAccount);
 
+        await writeChanges(`${dstDir}/${shard}`, allChangesByAccount);
+    }
+
+    async function *changesByAccountStream(shard, startBlockNumber, endBlockNumber) {
         for (let blockNumber = startBlockNumber; blockNumber < endBlockNumber; blockNumber += FILES_PER_ARCHIVE) {
             console.log('blockNumber', blockNumber, 'endBlockNumber', endBlockNumber);
             const blockHeight = normalizeBlockHeight(blockNumber);
             const [prefix1, prefix2] = blockHeight.match(/^(.{6})(.{3})/).slice(1);
-            const inFolder = `${dstDir}/${folder}/${prefix1}/${prefix2}`;
+            const inFolder = `${dstDir}/${shard}/${prefix1}/${prefix2}`;
             const inFile = `${inFolder}/${blockHeight}.tgz`;
-            // const uncompressStream = new compressing.tgz.UncompressStream({ source: inFile });
 
             console.log('inFile', inFile);
 
@@ -50,10 +60,11 @@ async function main() {
                 });
 
                 const { state_changes, chunk,  ...json } = JSON.parse(data.toString('utf-8'));
+                if (!chunk) {
+                    continue;
+                }
+
                 const blockHeight = chunk.header.height_included;
-                console.log('blockHeight', blockHeight);
-                // console.log('json', json);
-                // console.log('state_changes', state_changes);
 
                 for (let { type, change } of state_changes) {
                     const { account_id, ...changeData } = change;
@@ -71,10 +82,138 @@ async function main() {
                 }
             }
 
-            console.log('changesByAccount', changesByAccount);
+            yield changesByAccount;
         }
     }
-    
+}
+
+const MIN_CHANGES_PER_FILE = 1000;
+
+async function writeChanges(outFolder, changesByAccount) {
+    console.log('changesByAccount', changesByAccount);
+    for (let accountId in changesByAccount) {
+        const accountChanges = changesByAccount[accountId];
+        const totalChanges = Object.values(accountChanges).reduce((sum, changes) => sum + changes.length, 0);
+        if (totalChanges < MIN_CHANGES_PER_FILE) {
+            continue;
+        }
+
+        await writeChangesFile(`${outFolder}/${accountId}.dat`, { [accountId]: accountChanges });
+        delete changesByAccount[accountId];
+    }
+
+
+    await writeChangesFile(`${outFolder}/changes.dat`, changesByAccount);
+}
+
+const PAGE_SIZE = 64 * 1024;
+
+async function writeChangesFile(outPath, changesByAccount) {
+    console.log('writeChangesFile', outPath, Object.keys(changesByAccount).length);
+
+    const outStream = fs.createWriteStream(outPath);
+    const buffer = Buffer.alloc(PAGE_SIZE);
+    let offset = 0;
+    for (let accountId in changesByAccount) {
+        offset = buffer.writeUInt8(accountId.length, offset);
+        offset += buffer.write(accountId, offset);
+
+        const accountChanges = changesByAccount[accountId];
+
+        for (let key in accountChanges) {
+            const allChanges = accountChanges[key];
+
+            // NOTE: Changes arrays are split into chunks of 0xFF items
+            for (let i = 0; i < allChanges.length + 0xFF; i += 0xFF) {
+                const changes = allChanges.slice(i, i + 0xFF);
+
+                // TODO: Check max key length
+                offset = buffer.writeUInt8(key.length, offset);
+                offset += buffer.write(key, offset);
+
+                offset = buffer.writeUInt8(changes.length, offset);
+                for (let change of changes) {
+                    offset = buffer.writeInt32LE(change, offset);
+                }
+
+                // TODO: Adjust this as needed
+                if (offset > PAGE_SIZE - 1000) {
+                    console.log('Writing', outPath, offset);
+                    await new Promise((resolve, reject) => {
+                        outStream.write(buffer.slice(0, offset), e => e ? reject(e) : resolve());
+                    });
+                    offset = 0;
+                }
+            }
+        }
+    }
+
+    await new Promise((resolve, reject) => {
+        console.log('Writing', outPath, offset);
+        outStream.end(buffer.slice(0, offset), e => e ? reject(e) : resolve());
+    });
+}
+
+function reduceRecursive(items, fn) {
+    if (items.length === 0) {
+        throw new Error('Cannot reduce empty list');
+    }
+
+    if (items.length === 1) {
+        return items[0];
+    }
+
+    return fn(
+        reduceRecursive(items.slice(0, items.length / 2), fn),
+        reduceRecursive(items.slice(items.length / 2), fn));
+}
+
+function merge(a, b, fn) {
+    for (k in b) {
+        if (a[k]) {
+            a[k] = fn(a[k], b[k]);
+        } else {
+            a[k] = b[k];
+        }
+    }
+    return a;
+}
+
+function mergeChangesByAccount(changesByAccountList) {
+    return reduceRecursive(changesByAccountList, (a, b) => merge(a, b, mergeChanges));
+}
+
+function mergeChanges(a, b) {
+    return merge(a, b, mergeSortedArrays);
+}
+
+function mergeSortedArrays(a, b) {
+    const result = [];
+    let i = 0;
+    let j = 0;
+    while (i < a.length && j < b.length) {
+        if (a[i] < b[j]) {
+            result.push(a[i]);
+            i++;
+        } else if (a[i] > b[j]) {
+            result.push(b[j]);
+            j++;
+        } else {
+            result.push(a[i]);
+            i++;
+            j++;
+        }
+    }
+
+    for (; i < a.length; i++) {
+        result.push(a[i]);
+    }
+
+    for (; j < b.length; j++) {
+        result.push(b[j]);
+    }
+
+    return result;
 }
 
 function changeKey(type, changeData) {
@@ -82,16 +221,16 @@ function changeKey(type, changeData) {
     switch (type) {
         case 'account_update':
         case 'account_deletion':
-            return type;
+            return 'a:';
         case 'access_key_update':
         case 'access_key_deletion':
-            return `${type}:${changeData.public_key}`;
+            return `k:${changeData.public_key}`;
         case 'data_update':
         case 'data_deletion':
-            return `${type}:${changeData.key_base64}`;
+            return `d:${changeData.key_base64}`;
         case 'contract_code_update':
         case 'contract_code_deletion':
-            return `${type}`;
+            return 'c:';
         default:
             throw new Error(`Unknown type ${type}`);
     }