Bad scrolling performance

Hello. We recently upgraded our cluster from v7 to v8 and had to migrate from olivere/elastic package to this official client at some service.

But after that we met serious performance degradation, service started responding 6-8 times longer than with client we used before (after reverting to olivere/elastic degradation is gone so this is confirmed).

Our code is pretty simple, we just scroll searches in goroutine and push data to a channel, see code below:

this is how client created

c, err := elasticsearch.NewTypedClient(elasticsearch.Config{
    Addresses: []string{makeEsURL()},
    Username:  cfg.EsUser,
    Password:  cfg.EsPass,
})

this is how we build initial query

esResults := make(chan esResult, 1)
...
scroll := es.Search().
    Index(r.GetIndex()).
    Raw(strings.NewReader(r.GetQuery())).
    Size(cfg.EsScrollSize).
    Scroll("15s")

err := scrollEsQuery(ctx, scroll, esResults)

this is how it is processed

func scrollEsQuery(ctx context.Context, scroll *search.Search, esResults chan<- esResult) error {
    var scrollID string
    res, err := scroll.Do(ctx)
    if err != nil {
        return err
    }
    if len(res.Hits.Hits) == 0 {
        return nil
    }

    esResults <- newEsResult(res.Hits)

    if res.ScrollId_ != nil {
        scrollID = *res.ScrollId_
    }

    defer func() {
        if scrollID != "" {
            es.ClearScroll().ScrollId(scrollID).Do(gCtx)
        }
    }()

    for {
        res, err := es.Scroll().ScrollId(scrollID).Scroll("15s").Do(ctx)
        if err != nil {
            return err // something went wrong
        }
        if res.ScrollId_ != nil {
            scrollID = *res.ScrollId_
        }
        if len(res.Hits.Hits) == 0 {
            return nil
        }

        select {
        case <-ctx.Done():
            return gCtx.Err()
        case esResults <- newEsResult(res.Hits):
        }
    }
}

Code is pretty simple and i can't understand what can cause such a big performance difference, am I doing anything wrong?

elastic / go-elasticsearch

Bad scrolling performance #881