1Z0-068 · Question #163
You are managing a policy-managed three-instance RAC database. You ran database ADDM for the database and noticed gc current block congested and gc cr block congested waits. What are two possible…
The correct answer is A. The wait events indicate a delay in processing has occurred in the Global Cache Services (GCS), B. The wait times indicate that the blocks must wait after initiating a gc block request, for the round. Exam Questions, Study Guides, Practice Tests. Lead the way to help you pass any IT Certification exams, 100% Pass Guaranteed or Full Refund. Especially Cisco, Vendor: Oracle Exam Code: Citrix Exam Name: Oracle Database 12c: RAC and Grid Infrastructure Administrtion LPI, Nortel…
Question
You are managing a policy-managed three-instance RAC database. You ran database ADDM for the database and noticed gc current block congested and gc cr block congested waits. What are two possible reasons for these wait events?
Options
- AThe wait events indicate a delay in processing has occurred in the Global Cache Services (GCS),
- BThe wait times indicate that the blocks must wait after initiating a gc block request, for the round
- CThe wait events indicate that there is block contention resulting in multiple requests for access to
- DThe wait events indicate that the local instance making the request for current or consistent read
How the community answered
(42 responses)- A81% (34)
- C12% (5)
- D7% (3)
Explanation
Exam Questions, Study Guides, Practice Tests. Lead the way to help you pass any IT Certification exams, 100% Pass Guaranteed or Full Refund. Especially Cisco, Vendor: Oracle Exam Code: Citrix Exam Name: Oracle Database 12c: RAC and Grid Infrastructure Administrtion LPI, Nortel, EXIN and so on. Our Slogan: First Test, First Pass. Help you to pass any IT Certification exams at the first try. You can reach us at any of the email addresses listed below. Any problems about IT certification or our products, you could rely upon us, we will give you satisfactory answers in 24 hours.
Topics
Community Discussion
8
Otieno M.Jun 27, 2026A and B are your correct picks here. The word "congested" is doing all the heavy lifting in those wait event names. When you see gc current block congested or gc cr block congested, Oracle is telling you that a delay occurred inside GCS itself on the holding instance side, not simply that a block transfer happened, which makes A correct. The distinction matters because non-congested gc waits like gc current block received are normal one-hop transfers across the interconnect, whereas the congested variants mean the remote instance could not service the request promptly. B captures the other half of it, the requesting instance had to sit and wait beyond the expected round-trip window after sending the request, which is why ADDM surfaces these together as a performance concern. C is describing hot block contention, which is a different problem you would chase through gc buffer busy acquire or gc buffer busy release, and D is incomplete reasoning that fits many gc waits generically, not specifically the congested flavor.
Anjali D.Jun 28, 2026Otieno nailed the distinction between congested and non-congested waits, but I would add that when ADDM surfaces gc current block congested, your first move should be checking if the interconnect itself is saturated versus whether the LMS process on the holding node is the actual bottleneck, because the remediation path is completely different.
Anjali D.Jun 26, 2026A and B, GCS delay plus round-trip wait after initiating the request. Saw this exact wording on my exam last spring and almost picked C because "block contention" sounds so obvious for those wait events, but C is describing hot block contention which is a different scenario. The key is that gc current block congested and gc cr block congested specifically point to a processing delay inside GCS and a round-trip timing issue, not simply multiple processes fighting over the same block. Once our group broke that down in our Tuesday session it clicked. Anyone else remember getting tripped up by C here?
Luis F.Jun 4, 2026So I spent way too long on this one last night and I think A and B are the right picks here. The word "congested" in those wait events is actually the key signal, it specifically points to a delay inside the Global Cache Services layer itself, meaning GCS is not just slow to send blocks over the network but is actually backed up in processing the requests on the remote instance side. B is basically describing the same problem from the requester's perspective, where the local instance kicks off the block request and then just sits there waiting longer than a normal round trip because GCS is overwhelmed. C trips people up because "contention" sounds right for a multi-instance environment, but block contention waits have their own event names and the congested label is a specific diagnostic flag for GCS processing delays, not just competing sessions grabbing the same block. Genuine question though, does the number of instances in the cluster actually change how you interpret these waits? Like in a three-instance setup vs a two-instance one, would the congested threshold or the GCS processing overhead differ in a way that matters for tuning, or is it basically the same diagnosis regardless?
Ingrid P.Jun 7, 2026The instance count answer is worth a dedicated card: more instances multiply the GCS request fanout per block transfer, so congested waits tend to surface at lower per-session load in larger clusters, but the diagnostic interpretation stays identical because congested always means GCS processing backlog regardless of topology.
Hiroshi T.Jun 13, 2026C has to be one of the two correct picks here, because the Oracle documentation on Global Cache Services explicitly ties gc current block congested and gc cr block congested to situations where multiple sessions are requesting the same block, creating a queue that backs up the GCS layer. If you look at the RAC Performance Tuning Guide section on wait event analysis, block contention from hot objects is the textbook driver for these congested variants, as opposed to the plain gc current block or gc cr block waits which point to network round-trip latency instead.
Anjali D.Jun 14, 2026Hiroshi, you make a solid case for why those congested waits show up during hot-block scenarios, but the congested designation specifically flags that the GCS node is resource-bound, typically high CPU or heavy inter-node messaging load, which is what A and B describe. Block contention raises the volume of requests but it is the GCS processing bottleneck on the remote side that earns the "congested" label, not the contention itself. Anyone else want to weigh in before we lock this one in?
Ingrid P.Jun 20, 2026These two nailed it. When you see gc current block congested and gc cr block congested in ADDM, it means GCS is hitting delays (A) and the requesting instance is burning time waiting through the full interconnect round trip before it can even use the block (B). Card these together under "RAC global cache congestion vs contention" because a lot of people mix up the congested waits, which are about processing delays in GCS, with the plain gc current block waits, which just mean normal round-trip time with no delay component.