[20191106]12c DCD SQLNET.EXPIRE_TIME.txt

12之前DCD使用TNS包來"ping"客戶端，並且依賴底層TCP堆疊，這有時可能需要更長的時間。現在，在12c中，這種情況已經改變，
DCD探針由TCP Stack實現。DCD探測現在將使用TCP KEEPALIVE套接字選項來檢查連線是否仍然可用。

在linux下實際上使用如下引數:
# echo /proc/sys/net/ipv4/tcp_keepalive* | xargs   -n 1 strings -1 -f
/proc/sys/net/ipv4/tcp_keepalive_intvl: 75
/proc/sys/net/ipv4/tcp_keepalive_probes: 9
/proc/sys/net/ipv4/tcp_keepalive_time: 7200

--//引數解析:
/proc/sys/net/ipv4/tcp_keepalive_time    當keepalive起用的時候，TCP傳送keepalive訊息的頻度。預設是2小時。
/proc/sys/net/ipv4/tcp_keepalive_intvl   當探測沒有確認時，keepalive探測包的傳送間隔。預設是75秒。
/proc/sys/net/ipv4/tcp_keepalive_probes 如果對方不予應答，keepalive探測包的傳送次數。預設值是9。

要使用新的實現，請將sqlnet.ora中的SQLNET.EXPIRE_TIME設定為探測之間的時間量(以分鐘為單位)。如果作業系統支援TCP保持活動調
優，那麼Oracle Net將自動使用新方法。除了Solaris之外，所有平臺都支援新機制。

自己在linux下測試看看,首先找一臺12c的伺服器.

1.環境:
SYSTEM@192.168.2.8:1521/orclcdb> select banner from v$version;
BANNER
----------------------------------------------------------------------
Oracle Database 18c Enterprise Edition Release 18.0.0.0.0 - Production

--//修改sqlnet.ora.加入:
SQLNET.EXPIRE_TIME=1

--//在伺服器執行:
# tcpdump -i ens192 host 192.168.100.78 and not port 22 and port 1521 -nnn
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on ens192, link-type EN10MB (Ethernet), capture size 262144 bytes

10:27:24.369267 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [S], seq 2084757500, win 14600, options [mss 1460,sackOK,TS val 3040047700 ecr 0,nop,wscale 7], length 0
10:27:24.369360 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [S.], seq 2301856063, ack 2084757501, win 28960, options [mss 1460,sackOK,TS val 783854486 ecr 3040047700,nop,wscale 7], length 0
10:27:24.369724 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [.], ack 1, win 115, options [nop,nop,TS val 3040047700 ecr 783854486], length 0
10:27:24.370149 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [P.], seq 1:214, ack 1, win 115, options [nop,nop,TS val 3040047701 ecr 783854486], length 213
10:27:24.370173 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [.], ack 214, win 235, options [nop,nop,TS val 783854487 ecr 3040047701], length 0
10:27:24.385006 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [P.], seq 1:9, ack 214, win 235, options [nop,nop,TS val 783854502 ecr 3040047701], length 8
10:27:24.385316 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [.], ack 9, win 115, options [nop,nop,TS val 3040047716 ecr 783854502], length 0
10:27:24.385347 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [P.], seq 214:427, ack 9, win 115, options [nop,nop,TS val 3040047716 ecr 783854502], length 213
10:27:24.385437 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [P.], seq 9:41, ack 427, win 243, options [nop,nop,TS val 783854502 ecr 3040047716], length 32
10:27:24.385986 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [P.], seq 427:588, ack 41, win 115, options [nop,nop,TS val 3040047717 ecr 783854502], length 161
10:27:24.386110 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [P.], seq 41:168, ack 588, win 252, options [nop,nop,TS val 783854503 ecr 3040047717], length 127
10:27:24.387304 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [P.], seq 588:626, ack 168, win 115, options [nop,nop,TS val 3040047718 ecr 783854503], length 38
10:27:24.387441 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [P.], seq 168:409, ack 626, win 252, options [nop,nop,TS val 783854504 ecr 3040047718], length 241
10:27:24.388602 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [P.], seq 626:707, ack 409, win 123, options [nop,nop,TS val 3040047719 ecr 783854504], length 81
10:27:24.389389 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [P.], seq 409:435, ack 707, win 252, options [nop,nop,TS val 783854506 ecr 3040047719], length 26
10:27:24.391079 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [P.], seq 707:953, ack 435, win 123, options [nop,nop,TS val 3040047722 ecr 783854506], length 246
10:27:24.395129 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [P.], seq 435:825, ack 953, win 260, options [nop,nop,TS val 783854512 ecr 3040047722], length 390
10:27:24.396571 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [P.], seq 953:2350, ack 825, win 131, options [nop,nop,TS val 3040047727 ecr 783854512], length 1397
10:27:24.403496 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [P.], seq 825:2079, ack 2350, win 283, options [nop,nop,TS val 783854520 ecr 3040047727], length 1254
10:27:24.404466 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [P.], seq 2350:2410, ack 2079, win 154, options [nop,nop,TS val 3040047735 ecr 783854520], length 60
10:27:24.404593 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [P.], seq 2079:2174, ack 2410, win 283, options [nop,nop,TS val 783854521 ecr 3040047735], length 95
10:27:24.405061 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [P.], seq 2410:2670, ack 2174, win 154, options [nop,nop,TS val 3040047736 ecr 783854521], length 260
10:27:24.405336 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [P.], seq 2174:2949, ack 2670, win 305, options [nop,nop,TS val 783854522 ecr 3040047736], length 775
10:27:24.406164 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [P.], seq 2670:2691, ack 2949, win 174, options [nop,nop,TS val 3040047737 ecr 783854522], length 21
10:27:24.406329 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [P.], seq 2949:3121, ack 2691, win 305, options [nop,nop,TS val 783854523 ecr 3040047737], length 172
10:27:24.406771 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [P.], seq 2691:2983, ack 3121, win 193, options [nop,nop,TS val 3040047737 ecr 783854523], length 292
10:27:24.407113 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [P.], seq 3121:3302, ack 2983, win 327, options [nop,nop,TS val 783854524 ecr 3040047737], length 181
10:27:24.407816 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [P.], seq 2983:3349, ack 3302, win 213, options [nop,nop,TS val 3040047738 ecr 783854524], length 366
10:27:24.408082 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [P.], seq 3302:3534, ack 3349, win 348, options [nop,nop,TS val 783854525 ecr 3040047738], length 232
10:27:24.408494 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [P.], seq 3349:3691, ack 3534, win 232, options [nop,nop,TS val 3040047739 ecr 783854525], length 342
10:27:24.408665 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [P.], seq 3534:3948, ack 3691, win 370, options [nop,nop,TS val 783854525 ecr 3040047739], length 414
10:27:24.409099 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [P.], seq 3691:3727, ack 3948, win 252, options [nop,nop,TS val 3040047740 ecr 783854525], length 36
10:27:24.409173 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [P.], seq 3948:3965, ack 3727, win 370, options [nop,nop,TS val 783854526 ecr 3040047740], length 17
10:27:24.409445 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [P.], seq 3727:3740, ack 3965, win 252, options [nop,nop,TS val 3040047740 ecr 783854526], length 13
10:27:24.409504 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [P.], seq 3965:3982, ack 3740, win 370, options [nop,nop,TS val 783854526 ecr 3040047740], length 17
10:27:24.448834 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [.], ack 3982, win 252, options [nop,nop,TS val 3040047780 ecr 783854526], length 0

--//在192.168.100.78上登入伺服器,然後不要執行任何命令,前面的tcpdump就是登入時執行的一些sql語句輸出.

10:28:24.506778 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [.], ack 3740, win 370, options [nop,nop,TS val 783914624 ecr 3040047780], length 0
10:28:24.507079 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [.], ack 3982, win 252, options [nop,nop,TS val 3040107836 ecr 783854526], length 0
10:29:24.538784 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [.], ack 3740, win 370, options [nop,nop,TS val 783974656 ecr 3040107836], length 0
10:29:24.539073 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [.], ack 3982, win 252, options [nop,nop,TS val 3040167866 ecr 783854526], length 0
10:30:24.698784 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [.], ack 3740, win 370, options [nop,nop,TS val 784034816 ecr 3040167866], length 0
10:30:24.699109 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [.], ack 3982, win 252, options [nop,nop,TS val 3040228025 ecr 783854526], length 0

--//你可以發現每分鐘發出1個探查包.而使用11g你可以發現最大間隔是是 2 * SQLNET.EXPIRE_TIME.實際上我以前一直以為最大間隙是
--//僅僅出現在開始第1次實際上可以出現任何時間段.

SYSTEM@192.168.2.8:1521/orclcdb> select sysdate from dual ;
SYSDATE
-------------------
2019-11-06 10:33:11

# tcpdump -i ens192 host 192.168.100.78 and not port 22 and port 1521 -nnn
...
10:32:25.018782 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [.], ack 3740, win 370, options [nop,nop,TS val 784155136 ecr 3040288183], length 0
10:32:25.019083 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [.], ack 3982, win 252, options [nop,nop,TS val 3040348341 ecr 783854526], length 0
--//以下是執行select sysdate from dual ;的情況,可以看時間可以對上
10:33:11.435797 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [P.], seq 3740:4003, ack 3982, win 252, options [nop,nop,TS val 3040394756 ecr 783854526], length 263
10:33:11.436227 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [P.], seq 3982:4360, ack 4003, win 392, options [nop,nop,TS val 784201553 ecr 3040394756], length 378
10:33:11.436576 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [.], ack 4360, win 271, options [nop,nop,TS val 3040394757 ecr 784201553], length 0
10:33:11.436957 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [P.], seq 4003:4024, ack 4360, win 271, options [nop,nop,TS val 3040394758 ecr 784201553], length 21
10:33:11.437030 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [P.], seq 4360:4532, ack 4024, win 392, options [nop,nop,TS val 784201554 ecr 3040394758], length 172
10:33:11.476822 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [.], ack 4532, win 291, options [nop,nop,TS val 3040394798 ecr 784201554], length 0
10:34:11.514787 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [.], ack 4024, win 392, options [nop,nop,TS val 784261632 ecr 3040394798], length 0
10:34:11.515077 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [.], ack 4532, win 291, options [nop,nop,TS val 3040454834 ecr 784201554], length 0
10:35:11.674789 IP 192.168.2.8.1521 > 192.168.100.78.4164: Flags [.], ack 4024, win 392, options [nop,nop,TS val 784321792 ecr 3040454834], length 0
10:35:11.675108 IP 192.168.100.78.4164 > 192.168.2.8.1521: Flags [.], ack 4532, win 291, options [nop,nop,TS val 3040514992 ecr 784201554], length 0
--//依舊是1分鐘一個探查包.而且重新計時.

2.如果在11g下你看到的情況是這樣.

--//11g伺服器環境:
# echo /proc/sys/net/ipv4/tcp_keepalive* | xargs   -n 1 strings -1 -f
/proc/sys/net/ipv4/tcp_keepalive_intvl: 75
/proc/sys/net/ipv4/tcp_keepalive_probes: 9
/proc/sys/net/ipv4/tcp_keepalive_time: 7200

# grep -i expire /u01/app/oracle/product/11.2.0.4/dbhome_1/network/admin/sqlnet.ora
SQLNET.EXPIRE_TIME = 1

--//重啟監聽與資料庫.
--//注:我在測試時發現如果設定核心引數的情況下核心引數優先,這樣即使在sqlnet.ora中設定SQLNET.EXPIRE_TIME = 1也無效.
--//重啟監聽也不行,要重啟資料庫才有效.不知道為什麼?

# tcpdump -i eth0 host 192.168.98.6 and not port 22 and port 1521 -nnn
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes

--//從客戶端登入(192.168.100.40),不要執行任何sql語句:
# tcpdump -i eth0 host 192.168.98.6 and not port 22 and port 1521 -nnn
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
--//以下是client登入時的情況:
11:05:39.766334 IP 192.168.98.6.59486 > 192.168.100.78.1521: S 479106083:479106083(0) win 8192 <mss 1460,nop,wscale 2,nop,nop,sackOK>
11:05:39.766529 IP 192.168.100.78.1521 > 192.168.98.6.59486: S 510739750:510739750(0) ack 479106084 win 14600 <mss 1460,nop,nop,sackOK,nop,wscale 7>
11:05:39.766625 IP 192.168.98.6.59486 > 192.168.100.78.1521: . ack 1 win 16425
11:05:39.776001 IP 192.168.98.6.59486 > 192.168.100.78.1521: P 1:279(278) ack 1 win 16425
11:05:39.776028 IP 192.168.100.78.1521 > 192.168.98.6.59486: . ack 279 win 123
11:05:39.778722 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 1:9(8) ack 279 win 123
11:05:39.779030 IP 192.168.98.6.59486 > 192.168.100.78.1521: P 279:557(278) ack 9 win 16423
11:05:39.779182 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 9:41(32) ack 557 win 131
11:05:39.779589 IP 192.168.98.6.59486 > 192.168.100.78.1521: P 557:733(176) ack 41 win 16415
11:05:39.779986 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 41:168(127) ack 733 win 140
11:05:39.803917 IP 192.168.98.6.59486 > 192.168.100.78.1521: P 733:768(35) ack 168 win 16383
11:05:39.804505 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 168:386(218) ack 768 win 140
11:05:39.805787 IP 192.168.98.6.59486 > 192.168.100.78.1521: . 768:2228(1460) ack 386 win 16328
11:05:39.805822 IP 192.168.98.6.59486 > 192.168.100.78.1521: P 2228:3830(1602) ack 386 win 16328
11:05:39.805833 IP 192.168.100.78.1521 > 192.168.98.6.59486: . ack 3830 win 188
11:05:39.806765 IP 192.168.100.78.1521 > 192.168.98.6.59486: . 386:1846(1460) ack 3830 win 188
11:05:39.806776 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 1846:2886(1040) ack 3830 win 188
11:05:39.807212 IP 192.168.98.6.59486 > 192.168.100.78.1521: . ack 2886 win 16425
11:05:39.807463 IP 192.168.98.6.59486 > 192.168.100.78.1521: P 3830:4078(248) ack 2886 win 16425
11:05:39.824525 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 2886:3206(320) ack 4078 win 210
11:05:39.828530 IP 192.168.98.6.59486 > 192.168.100.78.1521: P 4078:5709(1631) ack 3206 win 16345
11:05:39.828559 IP 192.168.100.78.1521 > 192.168.98.6.59486: . ack 5709 win 236
11:05:39.866181 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 3206:4303(1097) ack 5709 win 236
11:05:39.867183 IP 192.168.98.6.59486 > 192.168.100.78.1521: P 5709:5765(56) ack 4303 win 16070
11:05:39.867597 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 4303:4492(189) ack 5765 win 236
11:05:39.868157 IP 192.168.98.6.59486 > 192.168.100.78.1521: P 5765:6096(331) ack 4492 win 16425
11:05:39.869704 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 4492:5229(737) ack 6096 win 259
11:05:39.870485 IP 192.168.98.6.59486 > 192.168.100.78.1521: P 6096:6117(21) ack 5229 win 16240
11:05:39.870901 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 5229:5341(112) ack 6117 win 259
11:05:39.871357 IP 192.168.98.6.59486 > 192.168.100.78.1521: P 6117:6405(288) ack 5341 win 16212
11:05:39.886440 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 5341:5462(121) ack 6405 win 281
11:05:39.887189 IP 192.168.98.6.59486 > 192.168.100.78.1521: P 6405:6816(411) ack 5462 win 16182
11:05:39.894197 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 5462:5975(513) ack 6816 win 304
11:05:39.894651 IP 192.168.98.6.59486 > 192.168.100.78.1521: P 6816:7250(434) ack 5975 win 16425
11:05:39.896968 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 5975:6251(276) ack 7250 win 327
11:05:39.897531 IP 192.168.98.6.59486 > 192.168.100.78.1521: P 7250:7600(350) ack 6251 win 16356
11:05:39.906603 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 6251:6395(144) ack 7600 win 330
11:05:39.907060 IP 192.168.98.6.59486 > 192.168.100.78.1521: P 7600:7930(330) ack 6395 win 16320
11:05:39.908517 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 6395:6709(314) ack 7930 win 330
11:05:39.908939 IP 192.168.98.6.59486 > 192.168.100.78.1521: P 7930:7962(32) ack 6709 win 16241
11:05:39.909376 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 6709:6736(27) ack 7962 win 330
11:05:39.909823 IP 192.168.98.6.59486 > 192.168.100.78.1521: P 7962:7975(13) ack 6736 win 16234
11:05:39.910193 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 6736:6763(27) ack 7975 win 330
11:05:40.110465 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 6736:6763(27) ack 7975 win 330
11:05:40.110789 IP 192.168.98.6.59486 > 192.168.100.78.1521: . ack 6763 win 16228 <nop,nop,sack 1 {6736:6763}>
---//等,不要執行任何sql語句:
11:07:39.799684 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 6763:6773(10) ack 7975 win 330
11:07:40.003365 IP 192.168.98.6.59486 > 192.168.100.78.1521: . ack 6773 win 16225
11:08:39.809941 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 6773:6783(10) ack 7975 win 330
11:08:40.010580 IP 192.168.98.6.59486 > 192.168.100.78.1521: . ack 6783 win 16223
11:09:39.820181 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 6783:6793(10) ack 7975 win 330
11:09:40.020849 IP 192.168.98.6.59486 > 192.168.100.78.1521: . ack 6793 win 16220
--//可以發現開始等2分鐘,後面才是1分鐘間隔.client執行如下:
SCOTT@192.168.100.78:1521/book> Select sysdate from dual;
SYSDATE
-------------------
2019-11-06 11:10:06

--//tcpdump -i eth0 host 192.168.98.6 and not port 22 and port 1521 -nnn的輸出,時間能對上.
11:10:06.196810 IP 192.168.98.6.59486 > 192.168.100.78.1521: P 7975:8237(262) ack 6793 win 16220
11:10:06.199010 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 6793:7071(278) ack 8237 win 330
11:10:06.200124 IP 192.168.98.6.59486 > 192.168.100.78.1521: P 8237:8258(21) ack 7071 win 16151
11:10:06.200509 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 7071:7183(112) ack 8258 win 330
11:10:06.407235 IP 192.168.98.6.59486 > 192.168.100.78.1521: . ack 7183 win 16123
---//等,不要執行任何sql語句:
11:11:39.830554 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 7183:7193(10) ack 8258 win 330
11:11:40.038339 IP 192.168.98.6.59486 > 192.168.100.78.1521: . ack 7193 win 16120
11:12:39.840753 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 7193:7203(10) ack 8258 win 330
11:12:40.041491 IP 192.168.98.6.59486 > 192.168.100.78.1521: . ack 7203 win 16118
11:13:39.850942 IP 192.168.100.78.1521 > 192.168.98.6.59486: P 7203:7213(10) ack 8258 win 330
11:13:40.052743 IP 192.168.98.6.59486 > 192.168.100.78.1521: . ack 7213 win 16115
--//你可以發現11.10:40沒有發出探查包,因為11:10:06有sql語句執行.然後在11:11:40再發出探測包.
--//你可以對比12c的情況,可以發現兩者的不同.12C在發出sql語句後重新計時.而11g是定時發出探測包(後面的時間秒數都是39或者40).

--//可以發現12c的這種改進更加科學.不會出現11g的情況,如果11g實際上最大間隔是2*EXPIRE_TIME.
--//換一句話講12c自動將sqlnet.ora中的SQLNET.EXPIRE_TIME設定為探測之間的時間量(以分鐘為單位)。

[20191106]12c DCD SQLNET.EXPIRE_TIME.txt

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