Switch pg backend to session-level advisory locking

[mars]

…to avoid rollback of partial state updates.

Based on discussion following merge of Postgres backend with @jbardin

Acceptance tests are once again passing locally ✅ (updated for commit 34fa67c)

$ TF_ACC=1 GO111MODULE=on go test -v -mod=vendor -timeout=2m -parallel=4 github.com/hashicorp/terraform/backend/remote-state/pg
=== RUN   TestBackend_impl
--- PASS: TestBackend_impl (0.00s)
=== RUN   TestBackendConfig
--- PASS: TestBackendConfig (0.06s)
    backend_test.go:50: TestBackendConfig on *pg.Backend with configs.synthBody{Filename:"<TestWrapConfig>", Values:map[string]cty.Value{"conn_str":cty.StringVal("postgres://localhost/terraform_backend_pg_test?sslmode=disable"), "schema_name":cty.StringVal("terraform_TestBackendConfig")}}
=== RUN   TestBackendStates
--- PASS: TestBackendStates (0.06s)
    backend_test.go:90: TestBackendConfig on *pg.Backend with configs.synthBody{Filename:"<TestWrapConfig>", Values:map[string]cty.Value{"conn_str":cty.StringVal("postgres://localhost/terraform_backend_pg_test?sslmode=disable"), "schema_name":cty.StringVal("terraform_TestBackendStates")}}
=== RUN   TestBackendStateLocks
--- PASS: TestBackendStateLocks (0.07s)
    backend_test.go:113: TestBackendConfig on *pg.Backend with configs.synthBody{Filename:"<TestWrapConfig>", Values:map[string]cty.Value{"schema_name":cty.StringVal("terraform_TestBackendStateLocks"), "conn_str":cty.StringVal("postgres://localhost/terraform_backend_pg_test?sslmode=disable")}}
    backend_test.go:119: TestBackendConfig on *pg.Backend with configs.synthBody{Filename:"<TestWrapConfig>", Values:map[string]cty.Value{"conn_str":cty.StringVal("postgres://localhost/terraform_backend_pg_test?sslmode=disable"), "schema_name":cty.StringVal("terraform_TestBackendStateLocks")}}
    backend_test.go:125: TestBackend: testing state locking for *pg.Backend
=== RUN   TestRemoteClient_impl
--- PASS: TestRemoteClient_impl (0.00s)
=== RUN   TestRemoteClient
--- PASS: TestRemoteClient (0.05s)
    client_test.go:34: TestBackendConfig on *pg.Backend with configs.synthBody{Filename:"<TestWrapConfig>", Values:map[string]cty.Value{"conn_str":cty.StringVal("postgres://localhost/terraform_backend_pg_test?sslmode=disable"), "schema_name":cty.StringVal("terraform_TestRemoteClient")}}
=== RUN   TestRemoteLocks
--- PASS: TestRemoteLocks (0.07s)
    client_test.go:63: TestBackendConfig on *pg.Backend with configs.synthBody{Filename:"<TestWrapConfig>", Values:map[string]cty.Value{"conn_str":cty.StringVal("postgres://localhost/terraform_backend_pg_test?sslmode=disable"), "schema_name":cty.StringVal("terraform_TestRemoteLocks")}}
    client_test.go:69: TestBackendConfig on *pg.Backend with configs.synthBody{Filename:"<TestWrapConfig>", Values:map[string]cty.Value{"conn_str":cty.StringVal("postgres://localhost/terraform_backend_pg_test?sslmode=disable"), "schema_name":cty.StringVal("terraform_TestRemoteLocks")}}
PASS
ok  	github.com/hashicorp/terraform/backend/remote-state/pg	0.453s

Also, have manually exercised terraform apply & destroy with this revised backend ✅

[jbardin]

Just to make sure I understand correctly the reason for the 2 lock attempts; this looks for an individual "workspace" entry with a lock, and if it didn't exist it takes a coarser lock on everything to make sure it's safe to create the workspace?

[mars]

Yes, that's right.

Although, what you've pointed out made me realize that there was a gap in this implementation. Once locked for creation [-1], after a new workspace's DB row is inserted, another DB session would have been able to lock that now existant row [the row's id], before the creation lock was unlocked.

I just pushed another rev that prevents taking a workspace-specific lock if already locked for creation.

[jbardin]

Thanks for the clarification, this makes sense now, especially with the latest update.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.