* add the query data deduplication excluding duplicated parts in MergeTree family engines.
query deduplication is based on parts' UUID which should be enabled first with merge_tree setting
assign_part_uuids=1
allow_experimental_query_deduplication setting is to enable part deduplication, default ot false.
data part UUID is a mechanism of giving a data part a unique identifier.
Having UUID and deduplication mechanism provides a potential of moving parts
between shards preserving data consistency on a read path:
duplicated UUIDs will cause root executor to retry query against on of the replica explicitly
asking to exclude encountered duplicated fingerprints during a distributed query execution.
NOTE: this implementation don't provide any knobs to lock part and hence its UUID. Any mutations/merge will
update part's UUID.
* add _part_uuid virtual column, allowing to use UUIDs in predicates.
Signed-off-by: Aleksei Semiglazov <asemiglazov@cloudflare.com>
address comments
Two new settings (by analogy with MergeTree family) has been added:
- `fsync_after_insert` - Do fsync for every inserted. Will decreases
performance of inserts.
- `fsync_tmp_directory` - Do fsync for temporary directory (that is used
for async INSERT only) after all part operations (writes, renames,
etc.).
Refs: #17380 (p1)
Contains error codes with number of times they have been triggered.
Columns:
- `name` ([String](../../sql-reference/data-types/string.md)) — name of the error (`errorCodeToName`).
- `code` ([Int32](../../sql-reference/data-types/int-uint.md)) — code number of the error.
- `value` ([UInt64](../../sql-reference/data-types/int-uint.md)) - number of times this error has been happened.
**Example**
``` sql
SELECT *
FROM system.errors
WHERE value > 0
ORDER BY code ASC
LIMIT 1
┌─name─────────────┬─code─┬─value─┐
│ CANNOT_OPEN_FILE │ 76 │ 1 │
└──────────────────┴──────┴───────┘
