[dnm] sql: use vectorized scan

[jordanlewis]

This commit clones the RowFetcher and associated encoding machinery so
that flows can be planned directly on top of columnarized output from
MVCCScan.

This is [dnm] because that cloning is pretty gross. It would be better to
teach the RowFetcher about both methods, potentially, to avoid having
to clone so much code. Some is probably unavoidable, though - the
decode methods I think will need to be cloned because they'll need to
understand about exec.ColBatch and friends.

A new session setting is added, experimental_vectorize, which
automatically replaces TableReaders with a colBatchScan operator
followed by a materialize operator. This automatic replacement is quite
hacky and another reason why this is [dnm].

This actually demonstrates something like 20% gains on COUNT and
things that use data from the scan, like SELECT SUM, without even
involving any other columnar operators. You can even see in
cockroach demo if you turn experimental_vectorize on and use only
the currently supported datatypes (int, float, string, bytes) and no nulls.

I thought that this was probably because we're batching the allocation
of the underlying memory for the data, but I don't think that's true,
because the materializer still has to create the same number of Datums
to do its job. So perhaps the speedup is due to the columnar
representation instead - fewer type switches when deserializing, since
it performs all of the decodes for a single column (which is a single
type) at once.

First 2 commits are from #31353.

Release note: None

[cockroach-teamcity]

This change is 

[cockroach-teamcity]

This change is 

[jordanlewis]

To put my money where my mouth is:

root@:26257/defaultdb> show create table a;
+------------+-----------------------------------------------+
| table_name |               create_statement                |
+------------+-----------------------------------------------+
| a          | CREATE TABLE a (                              |
|            |                                               |
|            |     a INT NOT NULL,                           |
|            |                                               |
|            |     b INT NULL,                               |
|            |                                               |
|            |     CONSTRAINT "primary" PRIMARY KEY (a ASC), |
|            |                                               |
|            |     FAMILY "primary" (a, b)                   |
|            |                                               |
|            | )                                             |
+------------+-----------------------------------------------+
(1 row)

Time: 7.036ms


root@:26257/defaultdb> insert into a select g,g+1 from generate_series(1,100000) g(g);

26257/defaultdb> select sum(a), sum(b) from a;                                                                                                                +------------+------------+
|    sum     |    sum     |
+------------+------------+
| 5000050000 | 5000150000 |
+------------+------------+
(1 row)

Time: 112.224ms

root@:26257/defaultdb> select sum(a), sum(b) from a;
+------------+------------+
|    sum     |    sum     |
+------------+------------+
| 5000050000 | 5000150000 |
+------------+------------+
(1 row)

Time: 104.331ms

root@:26257/defaultdb> select sum(a), sum(b) from a;
+------------+------------+
|    sum     |    sum     |
+------------+------------+
| 5000050000 | 5000150000 |
+------------+------------+
(1 row)

Time: 107.582ms

root@:26257/defaultdb> set experimental_vectorize=true;
SET

Time: 1.941ms

root@:26257/defaultdb> select sum(a), sum(b) from a;
+------------+------------+
|    sum     |    sum     |
+------------+------------+
| 5000148976 | 5000150000 |
+------------+------------+
(1 row)

Time: 83.114ms

root@:26257/defaultdb> select sum(a), sum(b) from a;
+------------+------------+
|    sum     |    sum     |
+------------+------------+
| 5000148976 | 5000150000 |
+------------+------------+
(1 row)

Time: 81.388ms

root@:26257/defaultdb> select sum(a), sum(b) from a;
+------------+------------+
|    sum     |    sum     |
+------------+------------+
| 5000148976 | 5000150000 |
+------------+------------+
(1 row)

Time: 80.507ms

[jordanlewis]

To put my money where my mouth is:

root@:26257/defaultdb> show create table a;
+------------+-----------------------------------------------+
| table_name |               create_statement                |
+------------+-----------------------------------------------+
| a          | CREATE TABLE a (                              |
|            |                                               |
|            |     a INT NOT NULL,                           |
|            |                                               |
|            |     b INT NULL,                               |
|            |                                               |
|            |     CONSTRAINT "primary" PRIMARY KEY (a ASC), |
|            |                                               |
|            |     FAMILY "primary" (a, b)                   |
|            |                                               |
|            | )                                             |
+------------+-----------------------------------------------+
(1 row)

Time: 7.036ms


root@:26257/defaultdb> insert into a select g,g+1 from generate_series(1,100000) g(g);

26257/defaultdb> select sum(a), sum(b) from a;                                                                                                                +------------+------------+
|    sum     |    sum     |
+------------+------------+
| 5000050000 | 5000150000 |
+------------+------------+
(1 row)

Time: 112.224ms

root@:26257/defaultdb> select sum(a), sum(b) from a;
+------------+------------+
|    sum     |    sum     |
+------------+------------+
| 5000050000 | 5000150000 |
+------------+------------+
(1 row)

Time: 104.331ms

root@:26257/defaultdb> select sum(a), sum(b) from a;
+------------+------------+
|    sum     |    sum     |
+------------+------------+
| 5000050000 | 5000150000 |
+------------+------------+
(1 row)

Time: 107.582ms

root@:26257/defaultdb> set experimental_vectorize=true;
SET

Time: 1.941ms

root@:26257/defaultdb> select sum(a), sum(b) from a;
+------------+------------+
|    sum     |    sum     |
+------------+------------+
| 5000148976 | 5000150000 |
+------------+------------+
(1 row)

Time: 83.114ms

root@:26257/defaultdb> select sum(a), sum(b) from a;
+------------+------------+
|    sum     |    sum     |
+------------+------------+
| 5000148976 | 5000150000 |
+------------+------------+
(1 row)

Time: 81.388ms

root@:26257/defaultdb> select sum(a), sum(b) from a;
+------------+------------+
|    sum     |    sum     |
+------------+------------+
| 5000148976 | 5000150000 |
+------------+------------+
(1 row)

Time: 80.507ms

[jordanlewis]

Hmm, just noticed that the results are wrong by "a little bit" - clearly there's a bug somewhere :) but I'm still pretty sure that the 20ms gain there isn't caused by whatever off-by-one error is in this idea.

[jordanlewis]

Hmm, just noticed that the results are wrong by "a little bit" - clearly there's a bug somewhere :) but I'm still pretty sure that the 20ms gain there isn't caused by whatever off-by-one error is in this idea.