diff --git a/packages/node-core/src/indexer/storeCache/cachePoi.spec.ts b/packages/node-core/src/indexer/storeCache/cachePoi.spec.ts
new file mode 100644
index 0000000000..18fae7ff45
--- /dev/null
+++ b/packages/node-core/src/indexer/storeCache/cachePoi.spec.ts
@@ -0,0 +1,161 @@
+// Copyright 2020-2022 OnFinality Limited authors & contributors
+// SPDX-License-Identifier: Apache-2.0
+
+import {Op} from 'sequelize';
+import {PoiRepo, ProofOfIndex} from '../entities';
+import {CachePoiModel} from './cachePoi';
+
+const mockPoiRepo = (): PoiRepo => {
+  const data: Record<number, any> = {};
+
+  const ascKeys = () => (Object.keys(data) as any[] as number[]).sort((a: number, b: number) => a - b);
+  const descKeys = () => [...ascKeys()].reverse();
+
+  return {
+    findByPk: (key: number) => ({toJSON: () => data[key]}),
+    findAll: ({limit, order, where}: any) => {
+      const orderedKeys = ascKeys();
+
+      const startHeight = where.id[Op.gte];
+
+      const filteredKeys = orderedKeys.filter((key) => key >= startHeight).slice(0, limit);
+
+      return filteredKeys.map((key) => ({toJSON: () => data[key]}));
+    },
+    findOne: ({order, where}: any) => {
+      const orderedKeys = descKeys();
+
+      if (!orderedKeys.length) {
+        return null;
+      }
+
+      if (!where) {
+        return {toJSON: () => data[orderedKeys[0]]};
+      }
+
+      // Only support null mmrRoot
+      for (const key of orderedKeys) {
+        if (data[key].mmrRoot !== null && data[key].mmrRoot !== undefined) {
+          return {toJSON: () => data[key]};
+        }
+      }
+
+      return null;
+    },
+    bulkCreate: (input: {id: number}[], opts: any) => input.map((d) => (data[d.id] = d)),
+    destroy: (key: number) => {
+      delete data[key];
+    },
+  } as any as PoiRepo;
+};
+
+const getEmptyPoi = (id: number, mmrRoot?: any): ProofOfIndex => {
+  return {
+    id,
+    chainBlockHash: new Uint8Array(),
+    hash: new Uint8Array(),
+    parentHash: new Uint8Array(),
+    mmrRoot,
+  } as ProofOfIndex;
+};
+
+describe('CachePoi', () => {
+  let poiRepo: PoiRepo;
+  let cachePoi: CachePoiModel;
+
+  beforeEach(() => {
+    poiRepo = mockPoiRepo();
+    cachePoi = new CachePoiModel(poiRepo);
+  });
+
+  describe('getPoiBlocksByRange', () => {
+    it('with mix of cache and db data', async () => {
+      await poiRepo.bulkCreate([{id: 1}, {id: 2}, {id: 3}] as any);
+
+      cachePoi.set(getEmptyPoi(4));
+      cachePoi.set(getEmptyPoi(5));
+      cachePoi.set(getEmptyPoi(6));
+
+      const res = await cachePoi.getPoiBlocksByRange(2);
+      expect(res.map((d) => d.id)).toEqual([2, 3, 4, 5, 6]);
+    });
+
+    it('only db data', async () => {
+      await poiRepo.bulkCreate([{id: 1}, {id: 2}, {id: 3}] as any);
+
+      const res = await cachePoi.getPoiBlocksByRange(2);
+      expect(res.map((d) => d.id)).toEqual([2, 3]);
+    });
+
+    it('only cache data', async () => {
+      cachePoi.set(getEmptyPoi(4));
+      cachePoi.set(getEmptyPoi(5));
+      cachePoi.set(getEmptyPoi(6));
+
+      const res = await cachePoi.getPoiBlocksByRange(2);
+      expect(res.map((d) => d.id)).toEqual([4, 5, 6]);
+    });
+  });
+
+  describe('getLatestPoi', () => {
+    it('with mix of cache and db data', async () => {
+      await poiRepo.bulkCreate([{id: 1}, {id: 2}, {id: 3}] as any);
+
+      cachePoi.set(getEmptyPoi(4));
+      cachePoi.set(getEmptyPoi(5));
+      cachePoi.set(getEmptyPoi(6));
+
+      const res = await cachePoi.getLatestPoi();
+      expect(res?.id).toBe(6);
+    });
+
+    it('only db data', async () => {
+      await poiRepo.bulkCreate([{id: 1}, {id: 2}, {id: 3}] as any);
+
+      const res = await cachePoi.getLatestPoi();
+      expect(res?.id).toBe(3);
+    });
+
+    it('only cache data', async () => {
+      cachePoi.set(getEmptyPoi(1));
+      cachePoi.set(getEmptyPoi(2));
+      cachePoi.set(getEmptyPoi(3));
+
+      const res = await cachePoi.getLatestPoi();
+      expect(res?.id).toBe(3);
+    });
+  });
+
+  describe('getLatestPoiWithMmr', () => {
+    it('with mix of cache and db data', async () => {
+      await poiRepo.bulkCreate([
+        {id: 1, mmrRoot: 'mmr1'},
+        {id: 2, mmrRoot: 'mmr2'},
+        {id: 3, mmrRoot: 'mmr3'},
+      ] as any);
+
+      cachePoi.set(getEmptyPoi(4, 'mmr4'));
+      cachePoi.set(getEmptyPoi(5));
+      cachePoi.set(getEmptyPoi(6));
+
+      const res = await cachePoi.getLatestPoiWithMmr();
+      expect(res?.id).toBe(4);
+    });
+
+    it('only db data', async () => {
+      await poiRepo.bulkCreate([{id: 1, mmrRoot: 'mmr1'}, {id: 2, mmrRoot: 'mmr2'}, {id: 3}] as any);
+
+      const res = await cachePoi.getLatestPoiWithMmr();
+      expect(res?.id).toBe(2);
+    });
+
+    it('only cache data', async () => {
+      cachePoi.set(getEmptyPoi(1, 'mmr1'));
+      cachePoi.set(getEmptyPoi(2, 'mmr2'));
+      cachePoi.set(getEmptyPoi(3));
+
+      const res = await cachePoi.getLatestPoiWithMmr();
+      expect(res?.id).toBe(2);
+    });
+  });
+});
diff --git a/packages/node-core/src/indexer/storeCache/cachePoi.ts b/packages/node-core/src/indexer/storeCache/cachePoi.ts
index fe8a6691e9..cd72385050 100644
--- a/packages/node-core/src/indexer/storeCache/cachePoi.ts
+++ b/packages/node-core/src/indexer/storeCache/cachePoi.ts
@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0
 
 import {u8aToBuffer} from '@subql/utils';
+import {Mutex} from 'async-mutex';
 import {Op, Transaction} from 'sequelize';
 import {getLogger} from '../../logger';
 import {PoiRepo, ProofOfIndex} from '../entities';
@@ -15,6 +16,7 @@ export class CachePoiModel implements ICachedModelControl {
   private setCache: Record<number, ProofOfIndex> = {};
   private removeCache: number[] = [];
   flushableRecordCounter = 0;
+  private mutex = new Mutex();
 
   constructor(readonly model: PoiRepo) {}
 
@@ -31,6 +33,7 @@ export class CachePoiModel implements ICachedModelControl {
   }
 
   async getById(id: number): Promise<ProofOfIndex | undefined> {
+    await this.mutex.waitForUnlock();
     if (this.removeCache.includes(id)) {
       logger.debug(`Attempted to get deleted POI with id="${id}"`);
       return undefined;
@@ -52,6 +55,7 @@ export class CachePoiModel implements ICachedModelControl {
   }
 
   async getPoiBlocksByRange(startHeight: number): Promise<ProofOfIndex[]> {
+    await this.mutex.waitForUnlock();
     const result = await this.model.findAll({
       limit: DEFAULT_FETCH_RANGE,
       where: {id: {[Op.gte]: startHeight}},
@@ -60,9 +64,7 @@ export class CachePoiModel implements ICachedModelControl {
 
     const resultData = result.map((r) => r?.toJSON<ProofOfIndex>());
 
-    const poiBlocks = Object.values(this.mergeResultsWithCache(resultData)).filter(
-      (poiBlock) => poiBlock.id >= startHeight
-    );
+    const poiBlocks = this.mergeResultsWithCache(resultData).filter((poiBlock) => poiBlock.id >= startHeight);
     if (poiBlocks.length !== 0) {
       return poiBlocks.sort((v) => v.id);
     } else {
@@ -71,34 +73,22 @@ export class CachePoiModel implements ICachedModelControl {
   }
 
   async getLatestPoi(): Promise<ProofOfIndex | null | undefined> {
+    await this.mutex.waitForUnlock();
     const result = await this.model.findOne({
       order: [['id', 'DESC']],
     });
 
-    if (!result) return null;
-
-    return Object.values(this.mergeResultsWithCache([result.toJSON()])).reduce((acc, val) => {
-      if (acc && acc.id < val.id) return acc;
-      return val;
-    }, null as ProofOfIndex | null);
+    return this.mergeResultsWithCache([result?.toJSON()], 'desc')[0];
   }
 
   async getLatestPoiWithMmr(): Promise<ProofOfIndex | null> {
+    await this.mutex.waitForUnlock();
     const result = await this.model.findOne({
       order: [['id', 'DESC']],
       where: {mmrRoot: {[Op.ne]: null}} as any, // Types problem with sequelize, undefined works but not null
     });
 
-    if (!result) {
-      return null;
-    }
-
-    return Object.values(this.mergeResultsWithCache([result.toJSON()]))
-      .filter((v) => !!v.mmrRoot)
-      .reduce((acc, val) => {
-        if (acc && acc.id < val.id) return acc;
-        return val;
-      }, null as ProofOfIndex | null);
+    return this.mergeResultsWithCache([result?.toJSON()], 'desc').find((v) => !!v.mmrRoot) ?? null;
   }
 
   get isFlushable(): boolean {
@@ -106,29 +96,44 @@ export class CachePoiModel implements ICachedModelControl {
   }
 
   async flush(tx: Transaction): Promise<void> {
-    logger.debug(`Flushing ${this.flushableRecordCounter} items from cache`);
-    const pendingFlush = Promise.all([
-      this.model.bulkCreate(Object.values(this.setCache), {transaction: tx, updateOnDuplicate: ['mmrRoot']}),
-      this.model.destroy({where: {id: this.removeCache}, transaction: tx}),
-    ]);
-
-    // Don't await DB operations to complete before clearing.
-    // This allows new data to be cached while flushing
-    this.clear();
-
-    await pendingFlush;
+    const release = await this.mutex.acquire();
+    try {
+      tx.afterCommit(() => {
+        release();
+      });
+      logger.debug(`Flushing ${this.flushableRecordCounter} items from cache`);
+      const pendingFlush = Promise.all([
+        this.model.bulkCreate(Object.values(this.setCache), {transaction: tx, updateOnDuplicate: ['mmrRoot']}),
+        this.model.destroy({where: {id: this.removeCache}, transaction: tx}),
+      ]);
+
+      // Don't await DB operations to complete before clearing.
+      // This allows new data to be cached while flushing
+      this.clear();
+
+      await pendingFlush;
+    } catch (e) {
+      release();
+      throw e;
+    }
   }
 
-  private mergeResultsWithCache(results: ProofOfIndex[]): Record<number, ProofOfIndex> {
+  private mergeResultsWithCache(results: (ProofOfIndex | undefined)[], order: 'asc' | 'desc' = 'asc'): ProofOfIndex[] {
     const copy = {...this.setCache};
 
-    results.map((result) => {
+    results.forEach((result) => {
       if (result) {
         copy[result.id] = result;
       }
     });
 
-    return copy;
+    const ascending = Object.values(copy).sort((a, b) => a.id - b.id);
+
+    if (order === 'asc') {
+      return ascending;
+    }
+
+    return ascending.reverse();
   }
 
   private clear(): void {