ClickHouse Recycles Small Objects Through Per-Size Free Lists
ClickHouse’s ArenaWithFreeLists keeps one free list per power-of-two size class and threads the free-list link through the freed block itself.
Posts
All posts published on this site.
Everything published here, newest first.
ClickHouse Rewrites the Query Before It Plans It
ClickHouse inlines aliases, runs 47 ordered tree passes, prunes columns and rewrites count(*) into a metadata read before planning.
ClickHouse Runs Distributed DDL Through a ZooKeeper Task Queue
Distributed DDL is a ZooKeeper queue of sequential entries plus a per-host finished directory that the initiator lists to collect results.
ClickHouse Short-Circuits AND and OR with a Mask and a Deferred Column
ClickHouse defers heavy and/or/if arguments into a thunk and runs them only on the rows a UInt8 mask leaves undecided.
ClickHouse's LRU Cache Keeps Its Order in a Linked List
ClickHouse’s LRU cache is a hash map of cells pointing into a linked list, so a lookup is an O(1) splice and eviction is a pop from the front.