sql: add pg_backend_pid column to crdb_internal.{node,cluster}_sessions

[nvanbenschoten]

Fixes #98581.
Informs #95771.

This commit adds a new pg_backend_pid column to the crdb_internal.node_sessions and crdb_internal.cluster_sessions tables.

Release note (sql change): A pg_backend_pid column was added to crdb_internal.node_sessions and crdb_internal.cluster_sessions. This value corresponds to the numerical ID returned from pg_backend_pid().

[cockroach-teamcity]

This change is 

[rafiss]

nice! just had suggestions for the comments

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @nvanbenschoten)

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pkg/server/serverpb/status.proto line 1052 at r1 (raw file):

    (gogoproto.stdduration) = true];

  // The Postgres backend PID of the session.

it might be useful to document the ways this differs from the Postgres PID. The following comments have more info, which might be useful to include here too so that people don't think this is actually a PID.

cockroach/pkg/sql/sem/builtins/pg_builtins.go

Lines 591 to 594 in 6581b36

	Info: "Returns a numerical ID attached to this session. This ID is " +
	"part of the query cancellation key used by the wire protocol. This " +
	"function was only added for compatibility, and unlike in Postgres, the " +
	"returned value does not correspond to a real process ID.",

cockroach/pkg/sql/pgwire/pgwirecancel/backend_key_data.go

Lines 19 to 27 in 343335a

	// BackendKeyData is a 64-bit identifier used by the pgwire protocol to cancel
	// queries. It is created at the time of session initialization. It contains the
	// SQLInstanceID of the node. SQLInstanceID is an alias of int32, but we use a
	// variable number of bits here. The leading bit will only be set if the
	// SQLInstanceID is greater than or equal to 2^11. If it is set, the other 31
	// bits are used for the ID; otherwise 11 bits are used for the ID. This is safe
	// because SQLInstanceID is always a non-negative integer. The remaining bits
	// (either 32 bits or 52 bits) are random, and are used to uniquely identify a
	// session on that SQL node.

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pkg/sql/crdb_internal.go line 2813 at r1 (raw file):

  status             STRING,         -- the status of the session (open, closed)
  session_end        TIMESTAMPTZ,    -- the time when the session was closed
  pg_backend_pid     INT             -- the postgres backend PID of the session

same for the comment here; it feels misleading to just say this is the same as the postgres backend PID.

[nvanbenschoten]

I'm actually not going to add this column to node_queries, cluster_queries, node_transactions, or cluster_transactions. It has such a specialized role and including it more widely might promote confusion or abuse.

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @rafiss)

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pkg/server/serverpb/status.proto line 1052 at r1 (raw file):

Previously, rafiss (Rafi Shamim) wrote…

it might be useful to document the ways this differs from the Postgres PID. The following comments have more info, which might be useful to include here too so that people don't think this is actually a PID.

cockroach/pkg/sql/sem/builtins/pg_builtins.go

Lines 591 to 594 in 6581b36

	Info: "Returns a numerical ID attached to this session. This ID is " +
	"part of the query cancellation key used by the wire protocol. This " +
	"function was only added for compatibility, and unlike in Postgres, the " +
	"returned value does not correspond to a real process ID.",

cockroach/pkg/sql/pgwire/pgwirecancel/backend_key_data.go

Lines 19 to 27 in 343335a

	// BackendKeyData is a 64-bit identifier used by the pgwire protocol to cancel
	// queries. It is created at the time of session initialization. It contains the
	// SQLInstanceID of the node. SQLInstanceID is an alias of int32, but we use a
	// variable number of bits here. The leading bit will only be set if the
	// SQLInstanceID is greater than or equal to 2^11. If it is set, the other 31
	// bits are used for the ID; otherwise 11 bits are used for the ID. This is safe
	// because SQLInstanceID is always a non-negative integer. The remaining bits
	// (either 32 bits or 52 bits) are random, and are used to uniquely identify a
	// session on that SQL node.

Done.

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pkg/sql/crdb_internal.go line 2813 at r1 (raw file):

Previously, rafiss (Rafi Shamim) wrote…

same for the comment here; it feels misleading to just say this is the same as the postgres backend PID.

Done.

[nvanbenschoten]

TFTR!

[nvanbenschoten]

bors r=rafiss

[craig]

Build succeeded:

• Bazel Essential CI (Cockroach)