Secondary Indexes

Indexes for ClickHouse tables

Moose lets you declare secondary/data-skipping indexes directly in your table definitions. Moose generates the ClickHouse INDEX clauses on create and plans ALTER TABLE ADD/DROP INDEX operations when you change them later.

When to use indexes

• Use indexes to optimize selective predicates on large tables, especially string and high-cardinality columns.
• Common types: minmax, Set(max_rows), ngrambf_v1(...), bloom_filter.

from moose_lib import OlapTable, OlapConfigfrom moose_lib.blocks import MergeTreeEnginefrom pydantic import BaseModel class Events(BaseModel):  id: str  user: str  message: str events_table = OlapTable[Events](  "Events",  OlapConfig(    engine=MergeTreeEngine(),    order_by_fields=["id"],    indexes=[      OlapConfig.TableIndex(name="idx_user", expression="user", type="minmax", granularity=1),      OlapConfig.TableIndex(name="idx_message_ngrams", expression="message", type="ngrambf_v1", arguments=["3","256","1","123"], granularity=1),    ],  ),)

• On create, Moose emits INDEX ... entries inside CREATE TABLE.
• On change, Moose plans ALTER TABLE DROP INDEX <name> then ADD INDEX ... if the definition changed; pure adds/drops are applied as single operations.