Blocktrees of sessions, including blockers and waiters
Comments
When a session must wait to acquire a lock, it is a waiter. The other session that already has the lock (and is causing the waiter to wait) is a blocker.
This collection contains rows for both the blocker sessions and the waiter sessions in the database. If the row is a blocker session, then BLKBY = 0. If the row is a waiter session, then the BLKBY column has information about its immediate blocker.
Waiters being blocked by a blocker can themselves also block other waiters, potentially forming a blocktree involving many sessions. Thus, a row can be a waiter and a blocker, in some cases (and can involve different locks).
Columns
| Name | Description |
|---|---|
| Session ID | Session ID |
| Serial # | Session serial # |
| Blked By | Blocker session ID (SID); 0 = the row is a blocker session |
| Block Count | Number of sessions being blocked, if the row is a blocker session |
| User | Login name |
Entity Requirements
| Attributes: | None |
|---|---|
| Minimum database version: | 8.1 |
Sample
