cockroachdb/cockroach: pkg/storage/pebble_merge.go; 16 LoC

Found a possible issue in [cockroachdb/cockroach](https://www.github.com/cockroachdb/cockroach) at [pkg/storage/pebble_merge.go](https://github.com/cockroachdb/cockroach/blob/4e3a9ccdb9cac89ae32d6248bb9b119b5bc250f7/pkg/storage/pebble_merge.go#L293-L308)

Below is the message reported by the analyzer for this snippet of code. Beware that the analyzer only reports the first
issue it finds, so please do not limit your consideration to the contents of the below message.

> function call which takes a reference to timeSeriesOp at line 307 may start a goroutine

[Click here to see the code in its original context.](https://github.com/cockroachdb/cockroach/blob/4e3a9ccdb9cac89ae32d6248bb9b119b5bc250f7/pkg/storage/pebble_merge.go#L293-L308)

Click here to show the 16 line(s) of Go which triggered the analyzer.

```go
for _, timeSeriesOp := range t.timeSeriesOps {
if timeSeriesOp.StartTimestampNanos != merged.StartTimestampNanos {
return nil, nil, errors.Errorf("start timestamp mismatch")
}
if timeSeriesOp.SampleDurationNanos != merged.SampleDurationNanos {
return nil, nil, errors.Errorf("sample duration mismatch")
}
if !isColumnar && len(timeSeriesOp.Offset) > 0 {
ensureColumnar(&merged)
ensureColumnar(&timeSeriesOp)
isColumnar = true
} else if isColumnar {
ensureColumnar(&timeSeriesOp)
}
proto.Merge(&merged, &timeSeriesOp)
}

```

Click here to show extra information the analyzer produced.

```
The following graphviz dot graph describes paths through the callgraph that could lead to a function calling a goroutine:
digraph G {
"(NewServer, 2)" -> {"(RegisterSignalHandler, 1)";"(Start, 3)";"(ServeHTTP, 2)";}
"(Stage, 6)" -> {"(execCmd, 3)";}
"(Merge, 2)" -> {"(New, 1)";}
"(newSklImpl, 1)" -> {"(clear, 1)";}
"(ServeHTTP, 2)" -> {"(getSession, 2)";}
"(QueryRowEx, 6)" -> {"(QueryEx, 6)";}
"(Start, 2)" -> {"(run, 3)";}
"(run, 3)" -> {"(MarkVerified, 3)";"(getBalance, 4)";"(getSession, 3)";"(setupTPCC, 4)";"(Release, 3)";}
"(setupTPCC, 4)" -> {"(Stage, 6)";}
"(runHistoryWithRetry, 4)" -> {"(runHistory, 4)";}
"(runHistory, 4)" -> {}
"(getBalance, 4)" -> {"(Query, 2)";}
"(verifySession, 2)" -> {"(QueryRowEx, 6)";}
"(initConnEx, 5)" -> {}
"(Release, 3)" -> {"(QueryEx, 6)";}
"(RegisterSignalHandler, 1)" -> {}
"(bgExec, 1)" -> {}
"(RunLimitedAsyncTask, 5)" -> {}
"(execCmdEx, 3)" -> {}
"(queryInternal, 6)" -> {"(execInternal, 6)";}
"(execInternal, 6)" -> {"(initConnEx, 5)";}
"(MarkVerified, 3)" -> {"(QueryEx, 6)";}
"(New, 1)" -> {"(newTreeImpl, 1)";"(newSklImpl, 1)";"(NewServer, 2)";}
"(run, 2)" -> {"(runHistoryWithRetry, 4)";}
"(clear, 1)" -> {"(Delete, 2)";}
"(Start, 3)" -> {"(Start, 2)";"(run, 2)";}
"(Delete, 2)" -> {"(Exec, 1)";}
"(QueryEx, 6)" -> {"(queryInternal, 6)";}
"(getSession, 3)" -> {"(Query, 2)";}
"(execCmd, 3)" -> {"(execCmdEx, 3)";}
"(getSession, 2)" -> {"(verifySession, 2)";}
"(newTreeImpl, 1)" -> {"(clear, 1)";}
"(Exec, 1)" -> {"(bgExec, 1)";}
"(Query, 2)" -> {"(RunLimitedAsyncTask, 5)";}
}

```

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commit ID: 4e3a9ccdb9cac89ae32d6248bb9b119b5bc250f7