How to deal with Elasticsearch index delay

Question

Here's my scenario:

I have a page that contains a list of users. I create a new user through my web interface and save it to the server. The server indexes the document in elasticsearch and returns successfully. I am then redirected to the list page which doesn't contain the new user because it can take up to 1-second for documents to become available for search in elasticsearch

Near real-time search in elasticsearch.

The elasticsearch guide says you can manually refresh the index, but says not to do it in production.

...don’t do a manual refresh every time you index a document in production; it will hurt your performance. Instead, your application needs to be aware of the near real-time nature of Elasticsearch and make allowances for it.

I'm wondering how other people get around this? I wish there was an event or something I could listen for that would tell me when the document was available for search but there doesn't appear to be anything like that. Simply waiting for 1-second is plausible but it seems like a bad idea because it presumably could take much less time than that.

Thanks!

I think the issue is you are trying to use a search database for transactional stuff. I might use a database that has true transactions and then use ElasticSearch for searching and advance filtering, not for list pages. — JT Turner, Jul 09 '20 at 21:08

Val · Accepted Answer · 2018-09-27T11:04:39.197

Even though you can force ES to refresh itself, you've correctly noticed that it might hurt performance. One solution around this and what people often do (myself included) is to give an illusion of real-time. In the end, it's merely a UX challenge and not really a technical limitation.

When redirecting to the list of users, you could artificially include the new record that you've just created into the list of users as if that record had been returned by ES itself. Nothing prevents you from doing that. And by the time you decide to refresh the page, the new user record would be correctly returned by ES and no one cares where that record is coming from, all the user cares about at that moment is that he wants to see the new record that he's just created, simply because we're used to think sequentially.

Another way to achieve this is by reloading an empty user list skeleton and then via Ajax or some other asynchronous way, retrieve the list of users and display it.

Yet another way is to provide a visual hint/clue on the UI that something is happening in the background and that an update is to be expected very shortly.

In the end, it all boils down to not surprise users but to give them enough clues as to what has happened, what is happening and what they should still expect to happen.

UPDATE:

Just for completeness' sake, this answer predates ES5, which introduced a way to make sure that the indexing call would not return until the document is either visible when searching the index or return an error code. By using ?refresh=wait_for when indexing your data you can be certain that when ES responds, the new data will be indexed.

And what happens when actually write has failed ? You made people believe it was created whereas it wan't true — user310291, Jan 28 '17 at 11:21
If the frontend shows that the write operation was successful but actually in the backend the write failed, then that would surprise the user on the next operation that what was saved is not there. The frontend can just show a flash to tell the user that it failed then reset to the truth. — Clutch, May 22 '18 at 23:52
@IvanDoroshenko Yes, it is: https://github.com/elastic/elasticsearch-net/blob/5e862d474fee44a7674879c953cfad7c517adeb1/src/Elasticsearch.Net/Domain/Enums.Generated.cs#L19 — Val, Jun 13 '19 at 14:17

tobigue · Answer 2 · 2016-12-07T14:22:05.067

10

Elasticsearch 5 has an option to block an indexing request until the next refresh ocurred:

?refresh=wait_for

See: https://www.elastic.co/guide/en/elasticsearch/reference/5.0/docs-refresh.html#docs-refresh

edited Dec 07 '16 at 14:22

answered Dec 07 '16 at 14:13

tobigue

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is ?refresh=wait_for supported by the NEST library? – Ivan Doroshenko Jun 13 '19 at 14:14

score 0 · Answer 3 · answered Aug 20 '19 at 16:15

Here is a fragment of code which is what I did in my Angular application to cope with this. In the component:

async doNewEntrySave() {
    try {
      const resp = await this.client.createRequest(this.doc).toPromise();
      this.modeRefreshDelay = true;
      setTimeout(() => {
        this.modeRefreshDelay = false;
        this.refreshPage();
      }, 2500);
    } catch (err) {
      this.error.postError(err);
    }
  }

In the template:

<div *ngIf="modeRefreshDelay">
  <h2>Waiting for update ...</h2>
</div>

I understand this is a quick-and-dirty solution but it illustrates how the user experience should work. Obviously it breaks if the real-world latency turns out to be more than 2.5 seconds. A fancier version would loop until the new record showed up in the page delay (with a limit of course).

Unless you completely redesign ElasticSearch you will always have some latency between the successful index operation and the time when that document shows up in search results.

score -2 · Answer 4 · answered Oct 10 '18 at 18:38

Data should be available immediately after indexing is complete. Couple of general questions:

Have you checked CPU and RAM to determine whether you are taxing your ES cluster? If so, you may need to beef up your hardware config to account for it. ES loves RAM!
Are you using NAS (network-attached-storage) or virtualized storage like EBS? Elastic recommends not doing so because of the latency. If you can use DAS (direct-attached) and SSD, you'll be in much, much better shape.

To give you an AWS example, moving from m4.xlarge instances to r3.xlarge made HUGE performance improvements for us.

How to deal with Elasticsearch index delay

4 Answers4

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