## New ElasticSearch storage option explanation in 9.2.0
Since v9.2.0, SkyWalking OAP provides 2 storage options for metrics/meter and records,
system environment variable is (`SW_STORAGE_ES_LOGIC_SHARDING`):
### No-Sharding Model (OAP default setting, `SW_STORAGE_ES_LOGIC_SHARDING = false`)
1. OAP merges all metrics/meter and records(without super datasets, such as segments) indices into one physical
index template `metrics-all` and `records-all`.
2. The logic index name would be present in columns `metric_table` and `record_table`.
3. If the logic column name has an alias (configured by `@ElasticSearch.Column()`), the alias would be the real physical column name.
### No-Sharding Model (`SW_STORAGE_ES_LOGIC_SHARDING = true `)
1. OAP shard metrics/meter indices into multi-physical indices as in the previous versions(one index template per metric/meter aggregation function).
2. Records and metrics without configuring aggregation function in `@MetricsFunction` and `@MeterFunction` would not be sharded.
3. The shard template name would be `metrics-aggregation function name` or `meter-aggregation function name` such as `metrics-count`,
and the logic index name would be present in column `metric_table`.
4. The OAP **would not** use the column alias, the logic column name would be the real physical column name.
**Notice**:
Users still could choose to adjust ElasticSearch's shard number(`SW_STORAGE_ES_INDEX_SHARDS_NUMBER`) to scale out no matter the option.
[Critical] Fix a low-performance issue of metrics persistent in the ElasticSearch storage implementation. One single metric could have to wait for an unnecessary 7~10s(System Env Variable SW_STORAGE_ES_FLUSH_INTERVAL).
This is a solid and critical performance issue, from the self-observability metric, we could find one metric that would need 7-10s to execute the data flush, which is not expected.
Optimize ElasticSearch query performance by using `_mGet` and physical index name rather than alias in these scenarios:
(a) Metrics aggregation
(b) Zipkin query
(c) Metrics query
(d) Log query
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kezhenxu94
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