Database Reference
In-Depth Information
Occasionally, a few blocks being lost (“hiccups”) over the interconnect may not affect the overall performance.
It's when blocks are consistently being lost on a continuous basis that diagnosis should look at getting to the root
cause of the issue. Blocks lost over the interconnect could be due to one or more of many reasons and should be
addressed to avoid poor response times for the users. The following query will help check for lost blocks:
Script: MVRACPDnTap_lostblocks.sql
SELECT A1.inst_id,
A3.instance_name,
A3.host_name,
A3.startup_time,
ROUND(SYSDATE - startup_time) "Days",
ROUND(( SYSDATE - startup_time ) * 24) "Hours",
A1.value "BLKL",
A1.value / ( ROUND(( SYSDATE - startup_time ) * 24) ) "Perhr",
A2.value "BLKC"
FROM gv$sysstat A1,
gv$sysstat A2,
gv$instance A3
WHERE A1.name = 'gc blocks lost'
AND A2.name = 'gc blocks corrupt'
AND A1.inst_id = A2.inst_id
AND A1.inst_id = A3.instance_number
ORDER BY 1;
Ins Instance Instance Uptime Uptime Blocks Blks Lost Blocks
ID Name Host Name Startup Time (Days) (Hours) Lost Per Hour Corrupt
--- --------- --------------------- ------------------- ------ ------- ------ --------- -------
1 SSKYDB_1 ssky4l4p3.localdomain 28-MAR-14 11:56:42 1 35 839 24 0
2 SSKYDB_2 ssky4l4p2.localdomain 28-MAR-14 12:06:49 1 35 36 1 0
3 SSKYDB_3 ssky4l4p4.localdomain 28-MAR-14 12:26:43 1 35 101 3 0
4 SSKYDB_4 ssky4l4p1.localdomain 28-MAR-14 12:15:59 1 35 98 3 0
There are several areas that may be the reason for blocks being lost over the interconnect:
Faulty or poorly configured cables/cards/switches
Poorly sized UDP receive buffer sizes and/or UDP buffer socket overflows
netstat -s reports packet
Poor interconnect performance and high CPU utilization:
reassembly failures
Network packet corruption resulting from UDP checksum errors and/or send/receive
transmission errors
Mismatched MTU sizes in the communication path
Interconnect LAN non-dedicated
Lack of server/switch adjacency
Outdated network driver or NIC firmware
Proprietary interconnect link transport and network protocol
Misconfigured bonding/link aggregation
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