diff --git a/packages/api/package.json b/packages/api/package.json
index c07a2c21..fd66f5cc 100644
--- a/packages/api/package.json
+++ b/packages/api/package.json
@@ -6,6 +6,7 @@
   "dependencies": {
     "@dbgate/engines": "^0.1.0",
     "@dbgate/sqltree": "^0.1.0",
+    "async-lock": "^1.2.4",
     "axios": "^0.19.0",
     "body-parser": "^1.19.0",
     "bufferutil": "^4.0.1",
diff --git a/packages/api/src/utility/JsonLinesDatastore.js b/packages/api/src/utility/JsonLinesDatastore.js
index 7ed08076..95e6845d 100644
--- a/packages/api/src/utility/JsonLinesDatastore.js
+++ b/packages/api/src/utility/JsonLinesDatastore.js
@@ -1,72 +1,39 @@
 const lineReader = require('line-reader');
+const AsyncLock = require('async-lock');
+const lock = new AsyncLock();
 
 class JsonLinesDatastore {
   constructor(file) {
     this.file = file;
     this.reader = null;
     this.readedDataRowCount = 0;
-
     this.readedSchemaRow = false;
-    this.isReading = false;
-    this.closeAfterRead = null;
-    this.closeAfterReadCallback = null;
-    this.closeAfterReadPromise = null;
-
-    this.waitForReadyPromise = null;
-    this.waitForReadyResolve = null;
-
-    // this.readerInfo = {
-    //   reader: null,
-    //   readedDataRowCount: 0,
-    //   readedSchemaRow: false,
-    //   isReading: false,
-    //   closeAfterRead: null,
-    //   closeAfterReadPromise: null,
-    // };
+    this.notifyChangedCallback = null;
   }
 
   closeReader() {
     if (!this.reader) return;
     const reader = this.reader;
     this.reader = null;
-    reader.close();
-  }
-
-  waitForReady() {
-    if (this.isReading) {
-      if (this.waitForReadyResolve) {
-        return this.waitForReadyPromise;
-      }
-      const promise = new Promise((resolve, reject) => {
-        this.waitForReadyResolve = resolve;
-      });
-      this.waitForReadyPromise = promise;
-      return promise;
-    }
-    return Promise.resolve();
+    this.readedDataRowCount = 0;
+    this.readedSchemaRow = false;
+    reader.close(() => {});
   }
 
   async notifyChanged(callback) {
-    if (this.isReading) {
-      this.closeAfterReadCallback = callback;
-      if (this.closeAfterRead) {
-        return this.closeAfterReadPromise;
-      }
-      const promise = new Promise((resolve, reject) => {
-        this.closeAfterRead = resolve;
-      });
-      this.closeAfterReadPromise = promise;
-      return promise;
-    } else {
+    this.notifyChangedCallback = callback;
+    await lock.acquire('reader', async () => {
       this.closeReader();
-    }
+    });
+    const call = this.notifyChangedCallback;
+    this.notifyChangedCallback = null;
+    if (call) call();
   }
 
   async openReader() {
     return new Promise((resolve, reject) =>
       lineReader.open(this.file, (err, reader) => {
         if (err) reject(err);
-
         resolve(reader);
       })
     );
@@ -89,24 +56,12 @@ class JsonLinesDatastore {
   }
 
   async ensureReader(offset) {
-    console.log('ENSURE', offset);
-    for (;;) {
-      await this.waitForReady();
-      if (this.readedDataRowCount > offset) {
-        this.closeReader();
-      }
-      if (!this.reader) {
-        const reader = await this.openReader();
-        if (this.isReading) {
-          reader.close(); // throw away this reader
-          continue; // reader is already used by other getRows, wait for free reader
-        }
-        this.reader = reader;
-        this.isReading = true;
-        break;
-      } else {
-        break;
-      }
+    if (this.readedDataRowCount > offset) {
+      this.closeReader();
+    }
+    if (!this.reader) {
+      const reader = await this.openReader();
+      this.reader = reader;
     }
     if (!this.readedSchemaRow) {
       await this.readLine(); // skip structure
@@ -117,30 +72,16 @@ class JsonLinesDatastore {
   }
 
   async getRows(offset, limit) {
-    await this.ensureReader(offset);
     const res = [];
-    for (let i = 0; i < limit; i += 1) {
-      const line = await this.readLine();
-      if (line == null) break;
-      res.push(JSON.parse(line));
-    }
-    this.isReading = false;
-    if (this.closeAfterRead) {
-      if (this.closeAfterReadCallback) this.closeAfterReadCallback();
-      this.closeReader();
-      const resolve = this.closeAfterRead;
-      this.closeAfterRead = null;
-      this.closeAfterReadPromise = null;
-      this.closeAfterReadCallback = null;
-      resolve();
-    }
-    if (this.waitForReadyResolve) {
-      const resolve = this.waitForReadyResolve;
-      this.waitForReadyResolve = null;
-      this.waitForReadyPromise = null;
-      resolve();
-    }
-    console.log('RETURN', res.length);
+    await lock.acquire('reader', async () => {
+      await this.ensureReader(offset);
+      for (let i = 0; i < limit; i += 1) {
+        const line = await this.readLine();
+        if (line == null) break;
+        res.push(JSON.parse(line));
+      }
+    });
+    // console.log('RETURN', res.length);
     return res;
   }
 }
diff --git a/yarn.lock b/yarn.lock
index aa5eee79..2f58d432 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2265,6 +2265,11 @@ async-limiter@~1.0.0:
   resolved "https://registry.yarnpkg.com/async-limiter/-/async-limiter-1.0.1.tgz#dd379e94f0db8310b08291f9d64c3209766617fd"
   integrity sha512-csOlWGAcRFJaI6m+F2WKdnMKr4HhdhFVBk0H/QbJFMCr+uO2kwohwXQPxw/9OCxp05r5ghVBFSyioixx3gfkNQ==
 
+async-lock@^1.2.4:
+  version "1.2.4"
+  resolved "https://registry.yarnpkg.com/async-lock/-/async-lock-1.2.4.tgz#80d0d612383045dd0c30eb5aad08510c1397cb91"
+  integrity sha512-UBQJC2pbeyGutIfYmErGc9RaJYnpZ1FHaxuKwb0ahvGiiCkPUf3p67Io+YLPmmv3RHY+mF6JEtNW8FlHsraAaA==
+
 async@0.2.10:
   version "0.2.10"
   resolved "https://registry.yarnpkg.com/async/-/async-0.2.10.tgz#b6bbe0b0674b9d719708ca38de8c237cb526c3d1"