write_* MergeTree table settings

These settings are available in system.merge_tree_settings and are autogenerated from ClickHouse source.

write_final_mark

Obsolete setting, does nothing.

write_marks_for_substreams_in_compact_parts

Enables writing marks per each substream instead of per each column in Compact parts. It allows to read individual subcolumns from the data part efficiently.

For example, column t Tuple(a String, b UInt32, c Array(Nullable(UInt32))) is serialized in the next substreams:

• t.a for String data of tuple element a
• t.b for UInt32 data of tuple element b
• t.c.size0 for array sizes of tuple element c
• t.c.null for null map of nested array elements of tuple element c
• t.c for UInt32 data pf nested array elements of tuple element c

When this setting is enabled, we will write a mark for each of these 5 substreams, which means that we will be able to read the data of each individual substream from the granule separately if needed. For example, if we want to read the subcolumn t.c we will read only data of substreams t.c.size0, t.c.null and t.c and won’t read data from substreams t.a and t.b. When this setting is disabled, we will write a mark only for top-level column t, which means that we will always read the whole column data from the granule, even if we need only data of some substreams.