planner

const (
	// ExecutionAutocommit: the steps run one at a time, in order, each in
	// its own implicit transaction — never inside an enclosing transaction
	// block. The CONCURRENTLY forms refuse an enclosing block outright,
	// and a multi-step sequence inside one block holds every earlier
	// step's locks across the steps designed to avoid them. A failed step
	// leaves partial state the runner must detect and recover before
	// retrying (a failed CONCURRENTLY build leaves an invalid index,
	// pg_index.indisvalid = false).
	ExecutionAutocommit Execution = "autocommit-each-step"
)

const (
	// ReasonMetadataOnly: a brief ACCESS EXCLUSIVE catalog change, no scan
	// and no rewrite.
	ReasonMetadataOnly Reason = "metadata-only"
	// ReasonOnlineIdiom: already the safe native form (CONCURRENTLY,
	// NOT VALID, VALIDATE, USING INDEX).
	ReasonOnlineIdiom Reason = "online-idiom"
	// ReasonFastDefault: ADD COLUMN with a constant default — the catalog
	// stores the default, no rewrite (PG 11+).
	ReasonFastDefault Reason = "fast-default"
	// ReasonBinaryCoercible: a type change PostgreSQL relabels without a
	// rewrite (widen varchar, varchar to text, widen numeric precision).
	ReasonBinaryCoercible Reason = "binary-coercible"
	// ReasonSaferIdiom: native, but the submitted form blocks; SaferSQL
	// carries the online rewrite when one can be constructed.
	ReasonSaferIdiom Reason = "safer-idiom"
	// ReasonAppBreakingRename: PostgreSQL executes the rename as a brief
	// metadata-only catalog flip, but it cannot land atomically across
	// running application instances — code still referencing the old
	// column or table name starts erroring the instant it commits. For a
	// column the safe sequence is expand/contract: add the new column,
	// dual-write and backfill, switch reads, then drop the old column as
	// its own reviewed change. For a table, coordinate the rename with
	// the application deploy that adopts the new name.
	ReasonAppBreakingRename Reason = "app-breaking-rename"
	// ReasonVolatileDefault: ADD COLUMN whose default the planner cannot
	// prove constant — PostgreSQL rewrites the table.
	ReasonVolatileDefault Reason = "volatile-default"
	// ReasonGeneratedStored: adding a stored generated column computes
	// every row — a full rewrite.
	ReasonGeneratedStored Reason = "generated-stored"
	// ReasonTypeRewrite: a type conversion PostgreSQL cannot relabel —
	// rewrite plus reindex.
	ReasonTypeRewrite Reason = "type-rewrite"
	// ReasonRelocation: SET TABLESPACE moves the heap — a rewrite-scale
	// copy.
	ReasonRelocation Reason = "relocation"
	// ReasonPartitionParentLock: creating a partition takes a brief ACCESS
	// EXCLUSIVE on the partitioned parent — no scan, but it queues behind
	// and then blocks every query on the parent while held.
	ReasonPartitionParentLock Reason = "partition-parent-lock"
	// ReasonUnsupportedOperation: the planner does not recognize the
	// operation or knows no safe path for it.
	ReasonUnsupportedOperation Reason = "unsupported-operation"
)

const (
	// RouteNative: PostgreSQL runs it online natively — directly or via
	// the safer idiom in Decision.SaferSQL.
	RouteNative Route = "native"
	// RouteCopyAndSwap: needs a table rewrite; only the engine's shadow
	// copy + cutover can do it online.
	RouteCopyAndSwap Route = "copy-and-swap"
	// RouteRefuse: no known safe path; not executed.
	RouteRefuse Route = "refuse"
)