Database Reference
In-Depth Information
Similarly, sending-side metrics for current mode block transfer can be broken down to individual statistics too.
The time taken by an LMS process to send a block to the remote side can be written as follows:
Gc current block receive time = Time take to send a message to LMS process by FG
+ (LMS) Time taken to pin block
(statistics: gc current block pin time)
+ (LMS) wait for log flush sync
( statistics: gc current block flush time)
+ (LMS) send time
(statistics: gc current block send time)
+ Wire latency.
Notice that the atomic steps involved in processing a current more transfer are slightly different from those
involved in CR mode transfer. The statistic
gc current block pin time
indicates the time taken by the LMS process
to pin a block. Higher latency for this statistic indicates that the blocks are currently pinned by another process and
imply that block was busy.
Your strategy to debug cache fusion performance issue should cover performance metrics of both sending side
and receiving side. Sending-side latency can lead to longer receiving-side latency.
Block Types Served
The pattern of block types served can be used to understand global cache workload patterns.
v$cr_block_server
provides a breakdown of CR requests into various types of requests. For example, the output in Listing 10-11 shows
that 51% of CR requests were for data block, 31% of CR requests for undo blocks, and 15% for undo header block.
From this output, you can infer that application affinity will greatly reduce the GC traffic, as 50% of the blocks served is
for undo blocks.
Listing 10-11.
Block Types Served
SELECT inst_id,
TRUNC(data_requests /tot_req,2) * 100 data_per,
TRUNC(undo_requests /tot_req,2) * 100 undo_per,
TRUNC(tx_requests /tot_req,2) * 100 tx_per,
TRUNC(other_requests/tot_req,2) * 100 other_per
FROM
(SELECT inst_id, cr_Requests + current_Requests tot_req,
data_requests, undo_requests, tx_requests, other_requests
FROM gv$cr_block_server
)
ORDER BY inst_id;
INST_ID DATA_PER UNDO_PER TX_PER OTHER_PER
---------- ---------- ---------- ---------- ----------
1 51 31 15 0
2 47 47 5 0
3 49 42 7 0
