sql: panic caused by DEALLOCATE ALL / DISCARD ALL inside of a prepared statement

[rafiss]

The issue described below is caused by this PR: #48842. This PR was backported to release-19.2 (#52444) and is currently pending approval for backporting to release-20.1 (#52443).

Describe the problem

The PGJDBC test suite caused a panic in CockroachDB. View the PGJDBC artifacts here and look at the snippet below.

E200815 09:33:45.840902 9975344 sql/conn_executor.go:789  [n1,client=127.0.0.1:53762,hostnossl,user=root] a SQL panic has occurred while executing the following statement:
DEALLOCATE ALL
E200815 09:33:45.841067 9975344 util/log/crash_reporting.go:138  [n1,client=127.0.0.1:53762,hostnossl,user=root] a panic has occurred!
portal  doesn't exist
(1) attached stack trace
  | github.com/cockroachdb/cockroach/pkg/sql.(*Server).ServeConn.func1
  | 	/go/src/github.com/cockroachdb/cockroach/pkg/sql/conn_executor.go:494
  | runtime.gopanic
  | 	/usr/local/go/src/runtime/panic.go:679
  | github.com/cockroachdb/cockroach/pkg/sql.(*connExecutor).exhaustPortal
  | 	/go/src/github.com/cockroachdb/cockroach/pkg/sql/conn_executor_prepare.go:402
  | github.com/cockroachdb/cockroach/pkg/sql.(*connExecutor).execPortal
  | 	/go/src/github.com/cockroachdb/cockroach/pkg/sql/conn_executor_exec.go:183
  | github.com/cockroachdb/cockroach/pkg/sql.(*connExecutor).execCmd
  | 	/go/src/github.com/cockroachdb/cockroach/pkg/sql/conn_executor.go:1465
  | github.com/cockroachdb/cockroach/pkg/sql.(*connExecutor).run
  | 	/go/src/github.com/cockroachdb/cockroach/pkg/sql/conn_executor.go:1338
  | github.com/cockroachdb/cockroach/pkg/sql.(*Server).ServeConn
  | 	/go/src/github.com/cockroachdb/cockroach/pkg/sql/conn_executor.go:496
  | github.com/cockroachdb/cockroach/pkg/sql/pgwire.(*conn).processCommandsAsync.func1
  | 	/go/src/github.com/cockroachdb/cockroach/pkg/sql/pgwire/conn.go:580
Wraps: (2) 2 safe details enclosed
Wraps: (3) attached stack trace
  | github.com/cockroachdb/cockroach/pkg/sql.(*Server).ServeConn.func1
  | 	/go/src/github.com/cockroachdb/cockroach/pkg/sql/conn_executor.go:494
  | runtime.gopanic
  | 	/usr/local/go/src/runtime/panic.go:679
  | [...repeated from below...]
Wraps: (4) assertion failure
Wraps: (5) attached stack trace
  | github.com/cockroachdb/cockroach/pkg/sql.(*connExecutor).exhaustPortal
  | 	/go/src/github.com/cockroachdb/cockroach/pkg/sql/conn_executor_prepare.go:402
  | github.com/cockroachdb/cockroach/pkg/sql.(*connExecutor).execPortal
  | 	/go/src/github.com/cockroachdb/cockroach/pkg/sql/conn_executor_exec.go:183
  | github.com/cockroachdb/cockroach/pkg/sql.(*connExecutor).execCmd
  | 	/go/src/github.com/cockroachdb/cockroach/pkg/sql/conn_executor.go:1465
  | github.com/cockroachdb/cockroach/pkg/sql.(*connExecutor).run
  | 	/go/src/github.com/cockroachdb/cockroach/pkg/sql/conn_executor.go:1338
  | github.com/cockroachdb/cockroach/pkg/sql.(*Server).ServeConn
  | 	/go/src/github.com/cockroachdb/cockroach/pkg/sql/conn_executor.go:496
  | github.com/cockroachdb/cockroach/pkg/sql/pgwire.(*conn).processCommandsAsync.func1
  | 	/go/src/github.com/cockroachdb/cockroach/pkg/sql/pgwire/conn.go:580
  | runtime.goexit
  | 	/usr/local/go/src/runtime/asm_amd64.s:1357
Wraps: (6) 2 safe details enclosed
Wraps: (7) portal  doesn't exist

To Reproduce

This happened when qualifying v19.2.10. It also happens on the current master branch.

The following PGTest reproduces the issue.

send
Query {"String": "CREATE TABLE rollbacktest (a INT, str TEXT)"}
----

until
ReadyForQuery
----
{"Type":"CommandComplete","CommandTag":"CREATE TABLE"}
{"Type":"ReadyForQuery","TxStatus":"I"}

# 80 = ASCII 'P' for Portal
send
Parse {"Name": "s1", "Query": "SELECT * FROM rollbacktest"}
Bind {"DestinationPortal": "p1", "PreparedStatement": "s1"}
Describe {"ObjectType": 80, "Name": "p1"}
Execute {"Portal": "p1"}
Sync
----

until
ReadyForQuery
----
{"Type":"ParseComplete"}
{"Type":"BindComplete"}
{"Type":"RowDescription","Fields":[{"Name":"a","TableOID":52,"TableAttributeNumber":1,"DataTypeOID":20,"DataTypeSize":8,"TypeModifier":-1,"Format":0},{"Name":"str","TableOID":52,"TableAttributeNumber":2,"DataTypeOID":25,"DataTypeSize":-1,"TypeModifier":-1,"Format":0}]}
{"Type":"CommandComplete","CommandTag":"SELECT 0"}
{"Type":"ReadyForQuery","TxStatus":"I"}


# 80 = ASCII 'P' for Portal
send
Parse {"Name": "s2", "Query": "DEALLOCATE ALL"}
Bind {"DestinationPortal": "p2", "PreparedStatement": "s2"}
Describe {"ObjectType": 80, "Name": "p2"}
Execute {"Portal": "p2"}
Sync
----

until
ReadyForQuery
----
{"Type":"ParseComplete"}
{"Type":"BindComplete"}
{"Type":"CommandComplete","CommandTag":"DEALLOCATE ALL"}
{"Type":"ReadyForQuery","TxStatus":"I"}