**Use case**
Clickhouse version 21.4
```
SELECT
    quantileTiming(0.95)(key) AS timing,
    quantileExact(0.95)(key) AS exact,
    quantileTDigest(0.95)(key) AS tdigest
FROM
(
    SELECT
        9000 AS key,
        2 AS count
    UNION ALL
    SELECT
        3000,
        11
    UNION ALL
    SELECT
        1000,
        26
)
ARRAY JOIN range(count) AS s

Query id: addce63f-0b75-46e2-b896-712d66711fb0

┌─timing─┬─exact─┬──tdigest─┐
│   9000 │  9000 │ 8123.076 │
└────────┴───────┴──────────┘


SELECT
    quantileTiming(0.9)(key) AS timing,
    quantileExact(0.9)(key) AS exact,
    quantileTDigest(0.9)(key) AS tdigest
FROM
(
    SELECT key
    FROM
    (
        SELECT
            9000 AS key,
            2 AS count
        UNION ALL
        SELECT
            3000,
            11
        UNION ALL
        SELECT
            1000,
            26
    )
    ARRAY JOIN range(count) AS s
    ORDER BY key ASC
)

Query id: e92e3d07-3b97-4155-aa10-9a15544d9312

┌─timing─┬─exact─┬───tdigest─┐
│   3000 │  3000 │ 6323.0757 │
└────────┴───────┴───────────┘

```

Probably related: https://github.com/tdunning/t-digest/issues/154
static Result & extractResult(Element & elem) { return elem; }
    };
    /** Adds a centroid `c` to the digest
     * centroid must be valid, validity is checked in add(), deserialize() and is maintained by compress()
      */
    void addCentroid(const Centroid & c)
    {
        centroids.push_back(c);
        count += c.count;
        ++unmerged;
        if (unmerged > params.max_unmerged)
            compress();
    }
    void compressBrute()
    {
        if (centroids.size() <= params.max_centroids)
            return;
        const size_t batch_size = (centroids.size() + params.max_centroids - 1) / params.max_centroids; 
        auto l = centroids.begin();
        auto r = std::next(l);
        BetterFloat sum = 0;
        BetterFloat l_mean = l->mean; 
        BetterFloat l_count = l->count;
        size_t batch_pos = 0;
        for (;r != centroids.end(); ++r)
        {
            if (batch_pos < batch_size - 1)