Blocking occurs when one session holds a lock on a resource and another session attempts to acquire a conflicting lock on the same resource, causing the second session to wait until the first releases it. In high-traffic SQL Server environments, blocking chains can grow quickly. A single long-running transaction can stall dozens of downstream sessions, degrading application response times and throughput.
The Blocking module gives you two complementary views of blocking activity across your monitored environment:
Overview — A multi-instance view that aggregates blocking events and chains across your environment or a filtered subset. Use this view to identify which instances, databases, objects, and SQL statements are responsible for the most blocking activity, measure cumulative impact, and prioritize remediation efforts.
Details — A single-instance deep dive that displays individual blocking events for a specific instance, including lead blocker statements, victim counts, start and end times, and wait details. Use this view when investigating a specific incident, tracing a blocking chain to its root cause, or reviewing the full context of a recurring blocker.
Key Capabilities
Identify High-Impact Blockers
WISdom aggregates blocking events by instance, database, lead blocker, and object into unique Blocker IDs. This grouping surfaces the SQL statements and objects causing the most cumulative wait time across your environment, so you can focus tuning efforts where they have the greatest effect.
Measure Blocking Impact
Blocking Impact tracks the cumulative wait time across all victims for a given blocking chain. Use this metric to quantify how much throughput a blocking statement is consuming and to justify optimization work with concrete data.
Analyze Access Patterns
The Blocks by Object view pivots blocking data from chain-level to object-level, showing which tables, indexes, and schemas are the most frequent sources of contention. Use this alongside Blocks by Chain when a specific object appears across multiple blocking chains.
Drill Into Individual Events
The Details screen provides event-level records for every blocking occurrence on a selected instance, including the lead blocker SQL statement, all involved sessions, wait types, wait resources, and application context. Use this data to reconstruct blocking chains and understand the conditions that produced them.
Navigating the Module
Toolbar and Filter Controls
Both screens share a common toolbar:
- Views — Apply a saved view configuration
- Tag — Filter by tags assigned to hosts, instances, or databases. Tags are user-defined groupings commonly used to identify business units, applications, environments, or dashboards. Filtering by tag targets all assets that share that tag. Tags are created and managed in the Tags section.
- Filters — Apply one or more filters from the filter panel
- Reset — Clear all active filters and return to the default view
The Filters panel provides the following options:
- Instance — Limit results to one or more monitored SQL Server instances
- Database — Filter to a specific database within the selected instance(s)
- Blocker ID — Filter to a specific aggregated blocking chain
- Application Host — Filter to blocking activity originating from a specific host machine
Filters applied on the Overview persist when navigating to the Details screen. The Details screen requires a single instance to be selected in the Instance filter. If multiple instances are in scope, narrow the selection to one before switching to Details.
Date Range
Use the Date Picker in the upper right corner of the page to set an explicit date and time range for blocking event analysis. The default range is the past seven days. For detailed instructions, see Using the Date Picker.
The navigation bar on the histogram provides two additional controls for adjusting the chart view without reopening the Date Picker:
- The back and forward arrows move the displayed range backward or forward by one block of the currently selected chart interval
- The double arrows move backward or forward by two blocks
- The Chart Interval selector sets the time window displayed on the chart. Available options are 1h, 6h, 12h, 1d, 3d, 7d, 14d, and 30d. The selected range is always anchored to the end date and time.
- The plot granularity selector (displayed as Auto with the current interval in parentheses, for example, Auto (3h)) controls how much data is grouped under each bar in the histogram. On the Blocking and Deadlocks screens, the default 7-day range uses the Auto (3h) setting. Other screens in WISdom display Auto (1h) for the same 7-day range.
For full details on both controls, see Chart Time Widget.
Most charts on the Overview also support direct time range selection by clicking and dragging on the chart. See Chart Time Widget for details.
Choosing Your View
Start with Overview when you want to:
- Identify which instances or databases have the most blocking activity
- Find SQL statements that are causing repeated or high-impact blocking
- Compare blocking frequency and impact across your environment
- Analyze blocking by the objects involved rather than by chain
Switch to Details when you want to:
- Investigate individual blocking events on a specific instance
- Review the lead blocker statement and victim sessions for a single event
- Analyze wait types, wait resources, and application context for a blocking chain
- Identify patterns in blocking event timing or duration
What's Next?
- Blocking – Overview — Complete guide to the Overview screen
- Blocking – Details — Complete guide to the Details screen