workload/bank: reset payload column before reuse

[ajkr]

Without this change, running the bank workload on a non-trivial number
of rows causes cockroach to fail with this error message:

panic: cannot overwrite value on flat Bytes: maxSetIndex=999, setIndex=0, consider using Reset

Release note: None

[cockroach-teamcity]

This change is 

[ajkr]

The test failure is relevant:

$ make test PKG=./pkg/ccl/storageccl/ TESTS=TestWorkloadStorage
...
--- FAIL: TestWorkloadStorage (0.00s)
    require.go:157:
                Error Trace:    export_storage_test.go:560
                Error:          Not equal:
                                expected: "0,0,initial-dTqn\n1,0,initial-Pkyk\n2,0,initial-eJkM\n3,0,initial-TlNb"
                                actual  : "0,0,\n1,0,\n2,0,\n3,0,"

                                Diff:
                                --- Expected
                                +++ Actual
                                @@ -1,4 +1,4 @@
                                -0,0,initial-dTqn
                                -1,0,initial-Pkyk
                                -2,0,initial-eJkM
                                -3,0,initial-TlNb
                                +0,0,
                                +1,0,
                                +2,0,
                                +3,0,
                Test:           TestWorkloadStorage
FAIL
FAIL    github.com/cockroachdb/cockroach/pkg/ccl/storageccl     0.058s
make: *** [Makefile:956: test] Error 1

[ajkr]

oh, AppendVal() doesn't play nicely with Reset() because resetting doesn't change the length to zero. There is probably something to be done about improving abstractions here.

[danhhz]

Thanks for the fix!

[danhhz]

fyi @asubiotto @jordanlewis on some potential usability feedback here

[ajkr]

bors r+

[craig]

Build failed

• GitHub CI (Cockroach)

[jordanlewis]

Thanks for kicking our tires - yeah, this appears like a rough corner. @asubiotto will take a look when he gets back from vacation in a week.

[jordanlewis]

Also cc @yuzefovich.

[ajkr]

bors r+

[craig]

Build succeeded

• GitHub CI (Cockroach)