Merge dev to main: add ProtectSession watchdog#796
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A non-canonical helper procedure that watches one designated session and decides what to do with whoever is blocking it. Classification reads sys.dm_tran_locks (not blocker.command), so SELECT-INTO-permanent and sessions that ran an UPDATE before their current statement are correctly identified as modifications. By default only reads and tempdb-only modifications are killed; permanent-data modifications are spared unless @kill_modification_blockers = 1 (kill them anyway) or @abort_on_modification_block = 1 (kill the protected session instead). Walks the blocking chain upstream for chain_depth + lead_blocker_session_id diagnostics; KILL target stays the immediate blocker. Resolves the contended resource (database + type + object name when OBJECT) for the debug output and kill/abort message. Defends against spid-reuse misfires by fingerprinting (session_id, login_time) and re-verifying before any KILL. Not added to Install-All; non-canonical helper. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Adds
ProtectSession, a non-canonical helper procedure that watches one designated session and decides what to do with whoever is blocking it.What is in this PR
ProtectSession/ProtectSession.sql-- the procedure (~770 lines)ProtectSession/README.md-- usage docs, parameter table, classification detailsNot added to Install-All; intentional, this is a non-canonical helper.
Highlights
Classification is held-lock-based, not command-based.
sys.dm_tran_locksis the source of truth for "is this blocker durably modifying permanent data" -- checkingcommandwould misclassifySELECT INTO dbo.RealTable(looks like a SELECT), and a session whose current statement is a SELECT but whose transaction still holds X locks from an earlier UPDATE. The proc looks for modification or schema-change locks (X / IX / U / SIX / BU / Sch-M) on OBJECT resources outside tempdb.Default behavior: kill SELECT blockers and tempdb-only modifications past
@block_threshold_seconds; leave permanent-data modifications alone. Override with@kill_modification_blockers = 1(kill them anyway, rolls back their work) or@abort_on_modification_block = 1(kill the protected session instead).Chain-walk diagnostics. Each cycle walks the blocking chain upstream to capture
chain_depth+lead_blocker_session_id-- surfaced in@debugoutput and in every kill/abort message. The KILL target stays the immediate blocker, since that is the only kill that directly frees the protected session.Contended-resource naming. From
sys.dm_tran_locksfor the protected session's WAIT row: database name, resource type, and object name (for OBJECT-type contention).Spid-reuse defense. SQL Server recycles freed
session_ids aggressively (confirmed empirically: 6 fresh connections all got the same recycled spid in sequence). The proc fingerprints sessions by(session_id, login_time)and re-verifies before any KILL, skipping with a log message on mismatch rather than misfiring on a recycled spid.🤖 Generated with Claude Code