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29
4
我正在尝试分析一个用 go 编写的应用程序，它显然使用了大约 256 个虚拟内存(使用 ps aux 检查)。我正在尝试使用 pprof打包并查看哪些函数分配/消耗了大部分内存，但结果对我来说毫无意义。 pprof top 似乎只列出了运行时函数。谁能帮我理解这些数据？
ps aux |grep android
root 4584 3.4 0.1 500244 29536 pts/1 Sl+ 17:21 0:38 ./android -logtostderr
转到工具 pprof http://localhost:6060/debug/pprof/heap
/pprof.localhost:6060.inuse_objects.inuse_space.008.pb.gz
Entering interactive mode (type "help" for commands)
(pprof) top
512.19kB of 512.19kB total ( 100%)
Dropped 19 nodes (cum <= 2.56kB)
flat flat% sum% cum cum%
512.19kB 100% 100% 512.19kB 100% runtime.malg
0 0% 100% 512.19kB 100% runtime.mcommoninit
0 0% 100% 512.19kB 100% runtime.mpreinit
0 0% 100% 512.19kB 100% runtime.rt0_go
0 0% 100% 512.19kB 100% runtime.schedinit
(pprof)
http://localhost:6060/debug/pprof/heap?debug=1
heap profile: 3: 49632 [3: 49632] @ heap/1048576
1: 49152 [1: 49152] @ 0x412c62 0x411bc9 0x6fd8c8 0x649c40 0x5497e6 0x409ad2 0x43615f 0x4669c1
# 0x6fd8c8 html.init+0xe8 /usr/local/gosrc/src/html/entity.go:2154
# 0x649c40 html/template.init+0x70 /usr/local/gosrc/src/html/template/url.go:105
# 0x5497e6 net/http/pprof.init+0x56 /usr/local/gosrc/src/net/http/pprof/pprof.go:239
# 0x409ad2 main.init+0x92 /root/go/src/github.com/ginkoob/devmg/local/android/local.go:236
# 0x43615f runtime.main+0x27f /usr/local/gosrc/src/runtime/proc.go:100
1: 384 [1: 384] @ 0x43d0e7 0x4317ef 0x437700 0x4372a9 0x464182
# 0x43d0e7 runtime.malg+0x27 /usr/local/gosrc/src/runtime/proc1.go:2172
# 0x4317ef runtime.mpreinit+0x1f /usr/local/gosrc/src/runtime/os1_linux.go:197
# 0x437700 runtime.mcommoninit+0x100 /usr/local/gosrc/src/runtime/proc1.go:114
# 0x4372a9 runtime.schedinit+0x79 /usr/local/gosrc/src/runtime/proc1.go:57
# 0x464182 runtime.rt0_go+0x132 /usr/local/gosrc/src/runtime/asm_amd64.s:109
1: 96 [1: 96] @ 0x449005 0x46a114 0x468625 0x467e71 0x4069d5 0x436190 0x4669c1
# 0x46a114 golang.org/x/mobile/gl.DoWork+0x54 /root/go/src/golang.org/x/mobile/gl/work.go:82
# 0x468625 golang.org/x/mobile/app.main+0x1d5 /root/go/src/golang.org/x/mobile/app/x11.go:65
# 0x467e71 golang.org/x/mobile/app.Main+0x21 /root/go/src/golang.org/x/mobile/app/app.go:22
# 0x4069d5 main.main+0x75 /root/go/src/github.com/ginkoob/devmg/local/android/local.go:65
# 0x436190 runtime.main+0x2b0 /usr/local/gosrc/src/runtime/proc.go:111
0: 0 [0: 0] @ 0x449005 0x6529f5 0x652936 0x64e2c4 0x54932e 0x549540 0x5222aa 0x523b0d 0x52457e 0x521d6e 0x4669c1
# 0x6529f5 runtime/pprof.writeGoroutineStacks+0x45 /usr/local/gosrc/src/runtime/pprof/pprof.go:514
# 0x652936 runtime/pprof.writeGoroutine+0x46 /usr/local/gosrc/src/runtime/pprof/pprof.go:505
# 0x64e2c4 runtime/pprof.(*Profile).WriteTo+0xd4 /usr/local/gosrc/src/runtime/pprof/pprof.go:236
# 0x54932e net/http/pprof.handler.ServeHTTP+0x37e /usr/local/gosrc/src/net/http/pprof/pprof.go:199
# 0x549540 net/http/pprof.Index+0x200 /usr/local/gosrc/src/net/http/pprof/pprof.go:211
# 0x5222aa net/http.HandlerFunc.ServeHTTP+0x3a /usr/local/gosrc/src/net/http/server.go:1422
# 0x523b0d net/http.(*ServeMux).ServeHTTP+0x17d /usr/local/gosrc/src/net/http/server.go:1699
# 0x52457e net/http.serverHandler.ServeHTTP+0x19e /usr/local/gosrc/src/net/http/server.go:1862
# 0x521d6e net/http.(*conn).serve+0xbee /usr/local/gosrc/src/net/http/server.go:1361
# runtime.MemStats
# Alloc = 2701264
# TotalAlloc = 2701264
# Sys = 7145720
# Lookups = 18
# Mallocs = 19841
# Frees = 0
# HeapAlloc = 2701264
# HeapSys = 3637248
# HeapIdle = 262144
# HeapInuse = 3375104
# HeapReleased = 0
# HeapObjects = 19841
# Stack = 557056 / 557056
# MSpan = 28896 / 32768
# MCache = 4832 / 16384
# BuckHashSys = 1443979
# NextGC = 4194304
# PauseNs = [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]
# NumGC = 0
# EnableGC = true
# DebugGC = false
http://localhost:6060/debug/pprof/goroutine?debug=1
goroutine profile: total 31
1 @ 0x652ba8 0x652983 0x64e2c4 0x54932e 0x549540 0x5222aa 0x523b0d 0x52457e 0x521d6e 0x4669c1
# 0x652ba8 runtime/pprof.writeRuntimeProfile+0xb8 /usr/local/gosrc/src/runtime/pprof/pprof.go:545
# 0x652983 runtime/pprof.writeGoroutine+0x93 /usr/local/gosrc/src/runtime/pprof/pprof.go:507
# 0x64e2c4 runtime/pprof.(*Profile).WriteTo+0xd4 /usr/local/gosrc/src/runtime/pprof/pprof.go:236
# 0x54932e net/http/pprof.handler.ServeHTTP+0x37e /usr/local/gosrc/src/net/http/pprof/pprof.go:199
# 0x549540 net/http/pprof.Index+0x200 /usr/local/gosrc/src/net/http/pprof/pprof.go:211
# 0x5222aa net/http.HandlerFunc.ServeHTTP+0x3a /usr/local/gosrc/src/net/http/server.go:1422
# 0x523b0d net/http.(*ServeMux).ServeHTTP+0x17d /usr/local/gosrc/src/net/http/server.go:1699
# 0x52457e net/http.serverHandler.ServeHTTP+0x19e /usr/local/gosrc/src/net/http/server.go:1862
# 0x521d6e net/http.(*conn).serve+0xbee /usr/local/gosrc/src/net/http/server.go:1361
1 @ 0x436573 0x444ce4 0x444242 0x46871a 0x467e71 0x4069d5 0x436190 0x4669c1
# 0x46871a golang.org/x/mobile/app.main+0x2ca /root/go/src/golang.org/x/mobile/app/x11.go:61
# 0x467e71 golang.org/x/mobile/app.Main+0x21 /root/go/src/golang.org/x/mobile/app/app.go:22
# 0x4069d5 main.main+0x75 /root/go/src/github.com/nme/devmg/local/android/local.go:65
# 0x436190 runtime.main+0x2b0 /usr/local/gosrc/src/runtime/proc.go:111
1 @ 0x4669c1
1 @ 0x436573 0x436634 0x436378 0x4669c1
# 0x436573 runtime.gopark+0x163 /usr/local/gosrc/src/runtime/proc.go:186
# 0x436634 runtime.goparkunlock+0x54 /usr/local/gosrc/src/runtime/proc.go:191
# 0x436378 runtime.forcegchelper+0xb8 /usr/local/gosrc/src/runtime/proc.go:152
1 @ 0x436573 0x436634 0x42630d 0x4669c1
# 0x436573 runtime.gopark+0x163 /usr/local/gosrc/src/runtime/proc.go:186
# 0x436634 runtime.goparkunlock+0x54 /usr/local/gosrc/src/runtime/proc.go:191
# 0x42630d runtime.bgsweep+0x14d /usr/local/gosrc/src/runtime/mgcsweep.go:67
1 @ 0x436573 0x436634 0x41e04a 0x4669c1
# 0x436573 runtime.gopark+0x163 /usr/local/gosrc/src/runtime/proc.go:186
# 0x436634 runtime.goparkunlock+0x54 /usr/local/gosrc/src/runtime/proc.go:191
# 0x41e04a runtime.runfinq+0xaa /usr/local/gosrc/src/runtime/mfinal.go:154
1 @ 0x436573 0x444ce4 0x444242 0x4691e7 0x4669c1
# 0x4691e7 golang.org/x/mobile/app.pump.func1+0x527 /root/go/src/golang.org/x/mobile/app/app.go:138
1 @ 0x436573 0x436634 0x40d611 0x40ccfb 0x4acb57 0x4669c1
# 0x4acb57 github.com/golang/glog.(*loggingT).flushDaemon+0x67 /root/go/src/github.com/golang/glog/glog.go:882
1 @ 0x4173be 0x45142e 0x4669c1
# 0x4173be runtime.notetsleepg+0x4e /usr/local/gosrc/src/runtime/lock_futex.go:203
# 0x45142e runtime.timerproc+0xde /usr/local/gosrc/src/runtime/time.go:209
1 @ 0x436573 0x444ce4 0x444242 0x533327 0x4669c1
# 0x533327 net/http.(*persistConn).readLoop+0xac7 /usr/local/gosrc/src/net/http/transport.go:983
1 @ 0x436573 0x43069e 0x42fb60 0x4cd99a 0x4cda06 0x4d158c 0x4ef94d 0x5254d1 0x524853 0x524716 0x524daf 0x408e1c 0x4669c1
# 0x42fb60 net.runtime_pollWait+0x60 /usr/local/gosrc/src/runtime/netpoll.go:157
# 0x4cd99a net.(*pollDesc).Wait+0x3a /usr/local/gosrc/src/net/fd_poll_runtime.go:73
# 0x4cda06 net.(*pollDesc).WaitRead+0x36 /usr/local/gosrc/src/net/fd_poll_runtime.go:78
# 0x4d158c net.(*netFD).accept+0x27c /usr/local/gosrc/src/net/fd_unix.go:408
# 0x4ef94d net.(*TCPListener).AcceptTCP+0x4d /usr/local/gosrc/src/net/tcpsock_posix.go:254
# 0x5254d1 net/http.tcpKeepAliveListener.Accept+0x41 /usr/local/gosrc/src/net/http/server.go:2138
# 0x524853 net/http.(*Server).Serve+0xb3 /usr/local/gosrc/src/net/http/server.go:1887
# 0x524716 net/http.(*Server).ListenAndServe+0x136 /usr/local/gosrc/src/net/http/server.go:1877
# 0x524daf net/http.ListenAndServe+0x8f /usr/local/gosrc/src/net/http/server.go:1967
# 0x408e1c main.main.func1+0x3c /root/go/src/github.com/nme/devmg/local/android/local.go:40
1 @ 0x436573 0x43069e 0x42fb60 0x4cd99a 0x4cda06 0x4cf74a 0x4e3c34 0x5c0c39 0x5c14aa 0x4b0cee 0x4b5b43 0x49e028 0x49a8d0 0x49b173 0x49cf47 0x4669c1
# 0x42fb60 net.runtime_pollWait+0x60 /usr/local/gosrc/src/runtime/netpoll.go:157
# 0x4cd99a net.(*pollDesc).Wait+0x3a /usr/local/gosrc/src/net/fd_poll_runtime.go:73
# 0x4cda06 net.(*pollDesc).WaitRead+0x36 /usr/local/gosrc/src/net/fd_poll_runtime.go:78
# 0x4cf74a net.(*netFD).Read+0x23a /usr/local/gosrc/src/net/fd_unix.go:232
# 0x4e3c34 net.(*conn).Read+0xe4 /usr/local/gosrc/src/net/net.go:132
# 0x5c0c39 bufio.(*Reader).fill+0x1e9 /usr/local/gosrc/src/bufio/bufio.go:97
# 0x5c14aa bufio.(*Reader).ReadByte+0x7a /usr/local/gosrc/src/bufio/bufio.go:229
# 0x4b0cee golang.org/x/net/websocket.hybiFrameReaderFactory.NewFrameReader+0xbe /root/go/src/golang.org/x/net/websocket/hybi.go:126
# 0x4b5b43 golang.org/x/net/websocket.Codec.Receive+0x183 /root/go/src/golang.org/x/net/websocket/websocket.go:315
# 0x49e028 golang.org/x/net/websocket.(Codec).Receive-fm+0x58 /root/go/src/github.com/nme/socks/ws.go:420
# 0x49a8d0 github.com/nme/socks.(*WSConn).execute+0x210 /root/go/src/github.com/nme/socks/ws.go:389
# 0x49b173 github.com/nme/socks.(*WSConn).receiveMessage+0x203 /root/go/src/github.com/nme/socks/ws.go:420
# 0x49cf47 github.com/nme/socks.(*WSConn).Setup.func3+0x117 /root/go/src/github.com/nme/socks/ws.go:221
1 @ 0x436573 0x436634 0x40d611 0x40ccfb 0x4080af 0x406fd8 0x4092e7 0x46937f 0x4669c1
# 0x4080af main.startSocks+0x3bf /root/go/src/github.com/nme/devmg/local/android/local.go:151
# 0x406fd8 main.startClient+0x5d8 /root/go/src/github.com/nme/devmg/local/android/local.go:82
# 0x4092e7 main.main.func2+0x227 /root/go/src/github.com/nme/devmg/local/android/local.go:64
# 0x46937f golang.org/x/mobile/app.main.func1+0x6f /root/go/src/golang.org/x/mobile/app/x11.go:51
1 @ 0x436573 0x444ce4 0x444242 0x533c4c 0x4669c1
# 0x533c4c net/http.(*persistConn).writeLoop+0x40c /usr/local/gosrc/src/net/http/transport.go:1016
1 @ 0x436573 0x436634 0x40d182 0x40ccfb 0x408f63 0x4669c1
# 0x408f63 main.main.func2.1+0x73 /root/go/src/github.com/nme/devmg/local/android/local.go:47
1 @ 0x436573 0x444ce4 0x444242 0x49dcee 0x4669c1
# 0x49dcee github.com/nme/socks.(*WSConn).Setup.func4+0x86e /root/go/src/github.com/nme/socks/ws.go:256
1 @ 0x436573 0x444ce4 0x444242 0x49c7a5 0x4669c1
# 0x49c7a5 github.com/nme/socks.SetKeepAlive.func1+0x215 /root/go/src/github.com/nme/socks/ws.go:32
1 @ 0x436573 0x436634 0x40d611 0x40ccfb 0x4072c6 0x4669c1
# 0x4072c6 main.WaitCmd+0xc6 /root/go/src/github.com/nme/devmg/local/android/local.go:95
1 @ 0x436573 0x444ce4 0x444242 0x4998aa 0x4669c1
# 0x4998aa github.com/nme/socks.(*Router).ListenAndServe+0x91a /root/go/src/github.com/nme/socks/ws.go:124
1 @ 0x436573 0x444ce4 0x444242 0x49a173 0x4669c1
# 0x49a173 github.com/nme/socks.(*WSConn).Setup+0x753 /root/go/src/github.com/nme/socks/ws.go:186
1 @ 0x436573 0x436634 0x40d611 0x40ccfb 0x49b3ea 0x4669c1
# 0x49b3ea github.com/nme/socks.(*Nic).Dial.func1+0x9a /root/go/src/github.com/nme/socks/conn.go:34
3 @ 0x436573 0x444ce4 0x444242 0x49cd50 0x4669c1
# 0x49cd50 github.com/nme/socks.(*Router).ListenAndServe.func1+0x590 /root/go/src/github.com/nme/socks/ws.go:96
1 @ 0x436573 0x43069e 0x42fb60 0x4cd99a 0x4cda06 0x4cf74a 0x4e3c34 0x51a734 0x581f7d 0x5c0c39 0x5c1aaa 0x5c1b23 0x6285f1 0x628360 0x515496 0x51d83f 0x5218a7 0x4669c1
# 0x42fb60 net.runtime_pollWait+0x60 /usr/local/gosrc/src/runtime/netpoll.go:157
# 0x4cd99a net.(*pollDesc).Wait+0x3a /usr/local/gosrc/src/net/fd_poll_runtime.go:73
# 0x4cda06 net.(*pollDesc).WaitRead+0x36 /usr/local/gosrc/src/net/fd_poll_runtime.go:78
# 0x4cf74a net.(*netFD).Read+0x23a /usr/local/gosrc/src/net/fd_unix.go:232
# 0x4e3c34 net.(*conn).Read+0xe4 /usr/local/gosrc/src/net/net.go:132
# 0x51a734 net/http.(*liveSwitchReader).Read+0xa4 /usr/local/gosrc/src/net/http/server.go:219
# 0x581f7d io.(*LimitedReader).Read+0xbd /usr/local/gosrc/src/io/io.go:427
# 0x5c0c39 bufio.(*Reader).fill+0x1e9 /usr/local/gosrc/src/bufio/bufio.go:97
# 0x5c1aaa bufio.(*Reader).ReadSlice+0x21a /usr/local/gosrc/src/bufio/bufio.go:328
# 0x5c1b23 bufio.(*Reader).ReadLine+0x53 /usr/local/gosrc/src/bufio/bufio.go:357
# 0x6285f1 net/textproto.(*Reader).readLineSlice+0x81 /usr/local/gosrc/src/net/textproto/reader.go:55
# 0x628360 net/textproto.(*Reader).ReadLine+0x40 /usr/local/gosrc/src/net/textproto/reader.go:36
# 0x515496 net/http.ReadRequest+0xb6 /usr/local/gosrc/src/net/http/request.go:653
# 0x51d83f net/http.(*conn).readRequest+0x32f /usr/local/gosrc/src/net/http/server.go:633
# 0x5218a7 net/http.(*conn).serve+0x727 /usr/local/gosrc/src/net/http/server.go:1319
1 @ 0x436573 0x43069e 0x42fb60 0x4cd99a 0x4cda06 0x4cf74a 0x4e3c34 0x51a734 0x581f7d 0x5c0c39 0x5c0e5c 0x51d7cb 0x5218a7 0x4669c1
# 0x42fb60 net.runtime_pollWait+0x60 /usr/local/gosrc/src/runtime/netpoll.go:157
# 0x4cd99a net.(*pollDesc).Wait+0x3a /usr/local/gosrc/src/net/fd_poll_runtime.go:73
# 0x4cda06 net.(*pollDesc).WaitRead+0x36 /usr/local/gosrc/src/net/fd_poll_runtime.go:78
# 0x4cf74a net.(*netFD).Read+0x23a /usr/local/gosrc/src/net/fd_unix.go:232
# 0x4e3c34 net.(*conn).Read+0xe4 /usr/local/gosrc/src/net/net.go:132
# 0x51a734 net/http.(*liveSwitchReader).Read+0xa4 /usr/local/gosrc/src/net/http/server.go:219
# 0x581f7d io.(*LimitedReader).Read+0xbd /usr/local/gosrc/src/io/io.go:427
# 0x5c0c39 bufio.(*Reader).fill+0x1e9 /usr/local/gosrc/src/bufio/bufio.go:97
# 0x5c0e5c bufio.(*Reader).Peek+0xcc /usr/local/gosrc/src/bufio/bufio.go:132
# 0x51d7cb net/http.(*conn).readRequest+0x2bb /usr/local/gosrc/src/net/http/server.go:629
# 0x5218a7 net/http.(*conn).serve+0x727 /usr/local/gosrc/src/net/http/server.go:1319
1 @ 0x436573 0x436634 0x42051b 0x4669c1
# 0x436573 runtime.gopark+0x163 /usr/local/gosrc/src/runtime/proc.go:186
# 0x436634 runtime.goparkunlock+0x54 /usr/local/gosrc/src/runtime/proc.go:191
# 0x42051b runtime.backgroundgc+0x8b /usr/local/gosrc/src/runtime/mgc.go:894
4 @ 0x436573 0x421717 0x4669c1
# 0x436573 runtime.gopark+0x163 /usr/local/gosrc/src/runtime/proc.go:186
# 0x421717 runtime.gcBgMarkWorker+0xf7 /usr/local/gosrc/src/runtime/mgc.go:1283
4584 是应用程序的 PID。猫/proc/4584/状态
Name: android
State: S (sleeping)
Tgid: 4584
Ngid: 0
Pid: 4584
PPid: 2776
TracerPid: 0
Uid: 0 0 0 0
Gid: 0 0 0 0
FDSize: 256
Groups: 0
NStgid: 4584
NSpid: 4584
NSpgid: 4584
NSsid: 2776
VmPeak: 631316 kB
VmSize: 573976 kB
VmLck: 0 kB
VmPin: 0 kB
VmHWM: 30060 kB
VmRSS: 29344 kB
VmData: 487492 kB
VmStk: 136 kB
VmExe: 6704 kB
VmLib: 13404 kB
VmPTE: 288 kB
VmPMD: 20 kB
VmSwap: 0 kB
Threads: 10
SigQ: 3/62942
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000000000
SigCgt: ffffffffffc1feff
CapInh: 0000000000000000
CapPrm: 0000003fffffffff
CapEff: 0000003fffffffff
CapBnd: 0000003fffffffff
Seccomp: 0
Cpus_allowed: f
Cpus_allowed_list: 0-3
Mems_allowed: 00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000001
Mems_allowed_list: 0
voluntary_ctxt_switches: 531158
nonvoluntary_ctxt_switches: 13254
最佳答案
Bradfitz 就如何使用 pprof 等工具分析 go 程序进行了精彩的演讲。
https://www.youtube.com/watch?v=xxDZuPEgbBU&feature=youtu.be
这是他在 github 上的演讲信息:
https://github.com/bradfitz/talk-yapc-asia-2015/blob/master/talk.md
希望对您有所帮助!
关于performance - 如何解释 pprof 输出？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/32078061/
29
4
0
我在一个项目中工作，该项目需要 SQL 结果的最佳性能，并且希望优化查询，但经过反复试验后，我在 IN 方面遇到了一些问题。 -- THIS RETURNS NO RESULTS AT ALL. SE
在尝试创建一个实际上非常简单的 SQL 语句时，我发现自己迷失了方向。 我有一个包含 3 个表的数据库: 食谱 - 存储一些用于 cooking 的食谱名称 配料食谱 - 将配料与食谱链接 成分 -
我正在尝试理解 PHP 中的 Hebrev 函数。 https://php.net/manual/en/function.hebrevc.php 它说:“将逻辑希伯来语文本转换为视觉文本”。但我不明白
嗨，我在 Grid view 的 android 文档中发现了一段代码对于以下代码。 gridview.setOnItemClickListener(new OnItemClickListener()
谁能解释一下 InfiniBand 是什么？与以太网相比的主要区别是什么，这些差异如何使其比以太网更快？ 在官方description从 mellanox 写到 Introduce InfiniBan
这个问题已经有答案了: How are java increment statements evaluated in complex expressions (1 个回答) 已关闭 8 年前。 我知道
我正在阅读 MySQL 教程，我遇到了这个: SELECT /*! SQL_NO_CACHE */ user FROM users; 为什么优化提示 SQL_NO_CACHE 包含在: /*!
我无法理解$(this)，我做了一个剪刀石头布的版本，并应用了 jQuery 让用户在计算机上选择按钮选项。我希望有人能解释一下 $(this) 指的是什么，它是 btn-primary 吗？该函数在
我不是很确定 while(choice == 1 || choice ==2);谁能解释一下。我明白这一点 if(choice ==1) displayMonthly(rainfall); e
let flyRight = CABasicAnimation(keyPath: "position.x") flyRight.toValue = view.bounds.size.width/2 f
目录 解释:int型默认值为0 但我们尝试发现并不能通过： 原因： int的默认值为0，而Integer的默认值为null
我正在处理一个查询，自从一个 SSRS 服务器传输到另一个服务器后，它似乎没有按预期执行，并且 where 语句的一部分中出现了以下行 找出不同之处，或者至少从我能找到的地方来看。 where COA
我正在制作一个退回检测程序，读取退回邮件。我们的设置是发送电子邮件，在发送的邮件中添加一个 noreply@domain.tl。一些收件人不再存在，因此我们想要读取退回邮件，并检测它发送给谁。我已经崩
我有一个关于公式通过控制点弯曲的问题。 如您所知，HTML Canvas 有 quadraticCurveTo(x1, y1, x2, y2)与 x1 and x2作为控制点。 但是，当您尝试使用它绘
我有一个 Emakefile看起来像: %% -- %% %% -- {'/Users/user/projects/custom_test/trunk/*', [debug_info, {out
我有一个非常简单的问题。这不仅适用于 spray-json，而且我已经阅读了 argonaut 和 circe 的类似声明。所以请赐教。 在 spray-json 中，我遇到了 There is no
我正在为视频添加水印。我试图让水印与视频尺寸成比例。我已经使用 scale2ref 看到了十几个不同的答案，但没有解释实际发生了什么，所以我发现很难知道如何实现/更改配置以适应我的情况。 当前覆盖命令
因为我正在学习语言，所以我在玩 Haskell，我只是发现了一些我不理解的东西，我找不到解释。如果我尝试运行此代码: map (`div` 0) [1,2,3,4] 我得到一个除以 0 的异常，这是预
我正在寻找解决错误对象引用未设置到对象实例的步骤/指南。以及问题发生原因的解释。 我正在寻找更一般的解释，所以如果我收到错误，我应该采取什么步骤来查找问题。我经常看到有人提供特定代码段的帖子，而其他人
我最近想升级我的知识React ，所以我从组件生命周期方法开始。让我好奇的第一件事是这个componentWillReceiveProps .所以，文档说当组件接收新的(不一定是更新的) Prop 时
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