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> > > Does it possible to modify table scan cardinality after persisting? I mean if we fix some bugs or support cardinality estimation for more operators later, should we update the existing persisten…
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RFC and the first PR: https://github.com/ClickHouse/ClickHouse/pull/53240
this issue is for dicussing what we will do in the future.
Use cases of column statistics:
- join reordering
- filter …
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We need more statistical information to provide a more precise cost estimation of plans.
- [x] #8046
- [ ] Histogram of values, used to estimate cardinality, **medium priority**
- [ ] Multi-colum…
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## Development Task
```
create table t1 (a int, b int);
create table t2 (a int, b int, key(a, b));
insert into t1 values (1, 10);
insert into t1 values (2, 9);
insert into t1 values (3, 8);
ins…
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**Is your feature request related to a problem? Please describe.**
I would like to be able to implement a GPU version of Spark's `approx_count_distinct` function, which uses the [HyperLogLog++](https…
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When available, use the the cardinality estimator's "union" feature to estimate the number of the partitions in the compaction result, instead of the sum I used. Note that for leveled compaction, the …
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### Proposal
I would like to propose a new metric type: Distinct Count.
A distinct count records the number of unique things placed into a set. However, exact precision is not required for perf…
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Idea by @nyh
Scylla already has a cardinality estimator (see http://www.datastax.com/dev/blog/improving-compaction-in-cassandra-with-cardinality-estimation) which estimates how many partitions the…
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## Development Task
```
mysql> set tidb_analyze_version=2;
Query OK, 0 rows affected (0.00 sec)
mysql> create table t (a int, b int, key(a, b));
Query OK, 0 rows affected (0.00 sec)
mysql> i…
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## Enhancement
Use the script to generate SQLs to prepare data:
```
print('create table t1 (a int, b int, c int, d int);')
print('create table t2 (a int, b int, c int, d int);')
print('create …