1 · INTERNALS · GLOSSARY 1/2
Glossary: Storage
TERM
WHAT IS IT, AND HOW IS IT DIFFERENT FROM TRADITIONAL DBMSs?
lab EXAMPLE
Table Engine
determines how data is written, stored, and read
Typically: a single storage mechanism for the entire DBMS
events: MergeTree
Part
a fixed set of lines on disk; created by insertion
202609_1_9_1
Partition
Partition groups by PARTITION BY: deletion, TTL, move
toYYYYMM(ts) → 202609
Merge
background consolidation of parts of a single partition into a larger one
5 parts → 1
Sorting Key
ORDER BY: the physical order of the rows in each part
(event_type, dt)
Primary key
sparse index on granules; default = ORDER BY
301 entries per section
Granule
наименьшая группа строк, которую читает запрос: до 8192
1 pellet out of 612
marks file
where, in the compressed file, each granule begins with a column
Usually: the index points directly to a row
event_type.cmrk2
Terms—as defined in the ClickHouse documentation glossary. For details on segments, partitions, merges, and indexes, see slides 8–11.