The SLM retention clean up task `SnapshotRetentionTask` lists all snapshots in order to identify the snapshots to retain and the snapshots to delete. While doing so it retrieves the full snapshot information, including shard snapshot details and shard snapshot failures, to later  only use snapshot metadata and snapshot timestamp to select the snapshots to retain. When the snapshots contain thousands of shards it represents of lot of objects that are unnecessary created, putting a lot of pressure on the garbage collector.

We should improve the way SLM retrieves snapshots to reduce the huge allocations of objects. David made some [interesting](https://github.com/elastic/elasticsearch/issues/99953#issuecomment-1738534389) [suggestions](https://github.com/elastic/elasticsearch/issues/99953#issuecomment-1738626743) in comments.

- #100044
- #100053
- #100054
- #100058
- #100065
- #100070
- #100092
x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/slm/SnapshotRetentionConfiguration.java
}
        if (maximumSnapshotCount != null) {
            builder.field(MAXIMUM_SNAPSHOT_COUNT.getPreferredName(), maximumSnapshotCount);
        }
        builder.endObject();
        return builder;
    }
    @Override
    public int hashCode() {
        return Objects.hash(expireAfter, minimumSnapshotCount, maximumSnapshotCount);
    }
    @Override
    public boolean equals(Object obj) {
        if (obj == null) {
            return false;
        }
        if (obj.getClass() != getClass()) {
            return false;
        }
        SnapshotRetentionConfiguration other = (SnapshotRetentionConfiguration) obj;
        return Objects.equals(this.expireAfter, other.expireAfter)
            && Objects.equals(minimumSnapshotCount, other.minimumSnapshotCount)
            && Objects.equals(maximumSnapshotCount, other.maximumSnapshotCount);
    }
    @Override
    public String toString() {
        return Strings.toString(this);
    }
}