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Un-sharding a ClickHouse Distributed Table into ReplicatedMergeTree

How to turn a sharded Distributed + MergeTree table into a single ReplicatedMergeTree table with a full copy on every node: freezing writes, creating the table with a shard-free ZooKeeper path, copying with INSERT ... SELECT, verifying with checksums, and cutting over safely. Rehearsed step by step on dummy data.

Can SayinOctober 20, 202610 min read

clickhouse replication sharding replicatedmergetree distributed migration

Bloom Filters in Analytical Databases - Part 3 - ClickHouse vs StarRocks

A side-by-side look at how ClickHouse and StarRocks use Bloom filters: granules vs pages, tunable vs automatic indexes, text search, join runtime filters, and how to verify each. Plus a decision guide for when to use what.

Can SayinOctober 13, 202611 min read

clickhouse starrocks bloom filter indexing runtime filter olap

Bloom Filters in Analytical Databases - Part 2 - StarRocks

How StarRocks uses Bloom filters in two very different places: page-level indexes stored on disk, and runtime filters built during joins. How to create them, verify them in the query profile, and know when they won't help.

Can SayinOctober 12, 202614 min read

starrocks bloom filter indexing runtime filter joins olap

Bloom Filters in Analytical Databases - Part 1 - ClickHouse

How ClickHouse uses Bloom filter skip indexes to avoid reading data, how to choose between bloom_filter, tokenbf_v1 and ngrambf_v1, how to size them, and how to tell whether they actually work.

Can SayinOctober 9, 202614 min read

clickhouse bloom filter indexing performance olap

Inside StarRocks Storage - Why the Fastest Read Is the One That Never Happens

A plain-language tour of StarRocks' storage hierarchy, from catalogs, partitions and tablets down to rowsets, segments and data pages, and how zone maps, bitmap indexes and bloom filters let queries skip most of the data without ever reading it.

Can SayinSeptember 25, 202619 min read

starrocks olap database clickhouse

ClickHouse 26.2 Broke insert_deduplicate = 0 - Why Your Re-Inserts Silently Vanish and How to Fix It

After upgrading to ClickHouse 26.2+, re-inserting identical data into Replicated tables can be silently dropped even though the insert reports success. Here's exactly why it happens and the right way to fix it.

Can SayinSeptember 21, 202611 min read

clickhouse deduplication replicatedmergetree upgrade insert