> ## Documentation Index
> Fetch the complete documentation index at: https://clickhouse.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# optimize_and_compare_chain_* session settings

> ClickHouse session settings in the optimize_and_compare_chain_* generated group.

export const SettingsInfoBlock = ({type, default_value, changeable_without_restart}) => {
  return <div className="not-prose" style={{
    display: "flex",
    flexWrap: "wrap",
    alignItems: "baseline",
    columnGap: "0.5rem",
    rowGap: "0.125rem",
    margin: "0.375rem 0",
    fontSize: "0.8125rem",
    lineHeight: "1.125rem"
  }}>
      <div style={{
    fontWeight: 600,
    opacity: 0.72
  }}>Type</div>
      <div style={{
    overflowWrap: "anywhere"
  }}>{type}</div>
      <div style={{
    fontWeight: 600,
    opacity: 0.72,
    marginInlineStart: "0.5rem"
  }}>Default</div>
      <div style={{
    overflowWrap: "anywhere"
  }}>{default_value}</div>
      {changeable_without_restart && <div style={{
    fontWeight: 600,
    opacity: 0.72,
    marginInlineStart: "0.5rem"
  }}>
          Changeable without restart
        </div>}
      {changeable_without_restart && <div style={{
    overflowWrap: "anywhere"
  }}>
          {changeable_without_restart}
        </div>}
    </div>;
};

These settings are available in [system.settings](/docs/reference/system-tables/settings) and are autogenerated from [source](https://github.com/ClickHouse/ClickHouse/blob/master/src/Core/Settings.cpp).

<h2 id="optimize_and_compare_chain">
  optimize\_and\_compare\_chain
</h2>

<SettingsInfoBlock type="Bool" default_value="1" />

<VersionHistory rows={[{"id": "row-1","items": [{"label": "25.2"},{"label": "1"},{"label": "A new setting"}]}]} />

Populate constant comparison in AND chains to enhance filtering ability. Support operators `<`, `<=`, `>`, `>=`, `=` and mix of them. For example, `(a < b) AND (b < c) AND (c < 5)` would be `(a < b) AND (b < c) AND (c < 5) AND (b < 5) AND (a < 5)`.

<h2 id="optimize_and_compare_chain_max_hash_work">
  optimize\_and\_compare\_chain\_max\_hash\_work
</h2>

<SettingsInfoBlock type="UInt64" default_value="5000000" />

<VersionHistory rows={[{"id": "row-1","items": [{"label": "26.7"},{"label": "5000000"},{"label": "New setting that bounds the work of the `optimize_and_compare_chain` optimization (measured in query-tree nodes hashed) so it cannot dominate analysis of queries with very many or very large `AND`-chains of comparisons. The previous value `0` (unlimited) reproduces the pre-26.7 behavior where the optimization was uncapped, so `compatibility` set to an earlier version keeps deriving transitive predicates without a budget. Set to `0` to disable the budget."}]}]} />

Work budget for the `optimize_and_compare_chain` optimization during query analysis, measured in the number of query-tree nodes hashed by `getTreeHash` (the dominant cost of this optimization). Once a query has hashed more than this many nodes while applying the optimization, it stops applying it for the rest of the query. This bounds analysis time for queries with very many or very large `AND`-chains of comparisons, where the optimization can otherwise dominate analysis while folding nothing. Stopping early is always safe: it only forgoes an optimization and never changes results. Set to `0` to disable the budget (unlimited).