Firebase 多组操作-最后将执行哪些操作？

当文件更改时，我必须与firebase同步。我知道如何在文件更改时设置处理程序，然后调用

Firebase.set

。但是，如果文件很大（9mb），例如，

set

操作需要30秒才能完成，同时文件再次更改，会发生什么情况呢？当在某些位置上进行设置并在同一位置上执行第二次设置时，会发生什么情况

Fb是否会自动取消正在进行的操作并重新启动

或者等到正在进行的操作完成后再重新开始

或者，最好监控在goven位置上的设置是否正在进行，以及是否在进行中的操作完成后排队等待下一个设置操作

---

样品试验

ref1 = new Firebase('https://my_firebase.firebaseio.com/some_location')
ref2 = new Firebase('https://my_firebase.firebaseio.com/some_location')
ref1.set({ some_large_data: 'abcef...' });
ref2.set({ some_large_data: '12345...' });
// which set will take effect on server? second? Or random (second that actually completes)?

---

如果我理解正确，您的问题是关于此流程：

客户端A开始上传一个巨大的文件

客户端B开始上载较小的文件

客户端B的上载完成

客户端A的上载完成

Firebase的服务器将以事务方式处理更新，因此不会发生部分更新

最后一次（完全）到达Firebase服务器的更新将在节点中结束

如果您想要控制这种类型的并发访问，可能最好使用工作队列。当然，Firebase也非常适合同步对此类工作队列的访问。：-）

---

因此，在上面的流程中，在第3步之前，不会在服务器上写入Firebase节点。在第4步之后，Firebase将写入大文件，并“忘记”客户端B中的小文件曾经存在。如果你想防止这种意外的重写，你可以考虑步骤0是“客户端锁定上传位置的<代码>事务< /代码>调用”。这将基本上在Firebase的乐观锁定方法之上实现悲观锁定。

因此，在测试之后，Firebase似乎将依次在服务器上执行所有

set

操作，即使在上一次远程完成之前在本地完成下一次操作，也不会取消其中任何操作

这意味着如果调用

set（）

100次，每个set操作都会影响远程数据（数据库）。对于我的用例来说，这是不好的，因为每次文件更改时，它都会完全上传到firebase。我必须编写自己的算法来决定何时与firebase同步数据

测试由两个脚本组成——一个是多次将数据写入同一firebase位置，另一个是从该位置读取数据

set_data.coffee

Firebase = require 'firebase'
firebaseUrl = 'https://my_firebase.firebaseio.com/same_location'

ref1 = new Firebase firebaseUrl
ref2 = new Firebase firebaseUrl
ref3 = new Firebase firebaseUrl

ref1.on 'value', (snapshot) -> console.log 'local same_location changed to ' + Buffer.byteLength((snapshot.val() or ''), 'utf8') + ' bytes'

data1 = ''
data2 = ''
data3 = ''
data1 += '1' for i in [1..1000*1000*2]
data2 += '2' for i in [1..1000*1000*3]
data3 += '3' for i in [1..100]

console.log 'data1 ' + Buffer.byteLength(data1, 'utf8') + ' bytes'
console.log 'data2 ' + Buffer.byteLength(data2, 'utf8') + ' bytes'
console.log 'data3 ' + Buffer.byteLength(data3, 'utf8') + ' bytes'

t1 = new Date()
ref1.set data1, (err) ->
  elapsed = new Date().getTime() - t1.getTime()
  console.log 'set1 finished ('+elapsed+'ms) - err is '+err
t2 = new Date()
ref2.set data2, (err) ->
  elapsed = new Date().getTime() - t2.getTime()
  console.log 'set2 finished ('+elapsed+'ms) - err is '+err
t3 = new Date()
ref3.set data3, (err) ->
  elapsed = new Date().getTime() - t3.getTime()
  console.log 'set3 finished ('+elapsed+'ms) - err is '+err

Firebase = require 'firebase'

firebaseUrl = 'https://my_firebase.firebaseio.com/same_location'

ref1 = new Firebase firebaseUrl

ref1.on 'value', (snapshot) -> console.log 'remote same_location changed to ' + Buffer.byteLength((snapshot.val() or ''), 'utf8') + ' bytes'

data1 2000000 bytes
data2 3000000 bytes
data3 100 bytes
local same_location changed to 2000000 bytes
local same_location changed to 3000000 bytes
local same_location changed to 100 bytes
set1 finished (118314ms) - err is null
set2 finished (149844ms) - err is null
set3 finished (149845ms) - err is null

remote same_location changed to 0 bytes
remote same_location changed to 2000000 bytes
remote same_location changed to 3000000 bytes
remote same_location changed to 100 bytes

喝咖啡

Firebase = require 'firebase'
firebaseUrl = 'https://my_firebase.firebaseio.com/same_location'

ref1 = new Firebase firebaseUrl
ref2 = new Firebase firebaseUrl
ref3 = new Firebase firebaseUrl

ref1.on 'value', (snapshot) -> console.log 'local same_location changed to ' + Buffer.byteLength((snapshot.val() or ''), 'utf8') + ' bytes'

data1 = ''
data2 = ''
data3 = ''
data1 += '1' for i in [1..1000*1000*2]
data2 += '2' for i in [1..1000*1000*3]
data3 += '3' for i in [1..100]

console.log 'data1 ' + Buffer.byteLength(data1, 'utf8') + ' bytes'
console.log 'data2 ' + Buffer.byteLength(data2, 'utf8') + ' bytes'
console.log 'data3 ' + Buffer.byteLength(data3, 'utf8') + ' bytes'

t1 = new Date()
ref1.set data1, (err) ->
  elapsed = new Date().getTime() - t1.getTime()
  console.log 'set1 finished ('+elapsed+'ms) - err is '+err
t2 = new Date()
ref2.set data2, (err) ->
  elapsed = new Date().getTime() - t2.getTime()
  console.log 'set2 finished ('+elapsed+'ms) - err is '+err
t3 = new Date()
ref3.set data3, (err) ->
  elapsed = new Date().getTime() - t3.getTime()
  console.log 'set3 finished ('+elapsed+'ms) - err is '+err

Firebase = require 'firebase'

firebaseUrl = 'https://my_firebase.firebaseio.com/same_location'

ref1 = new Firebase firebaseUrl

ref1.on 'value', (snapshot) -> console.log 'remote same_location changed to ' + Buffer.byteLength((snapshot.val() or ''), 'utf8') + ' bytes'

data1 2000000 bytes
data2 3000000 bytes
data3 100 bytes
local same_location changed to 2000000 bytes
local same_location changed to 3000000 bytes
local same_location changed to 100 bytes
set1 finished (118314ms) - err is null
set2 finished (149844ms) - err is null
set3 finished (149845ms) - err is null

remote same_location changed to 0 bytes
remote same_location changed to 2000000 bytes
remote same_location changed to 3000000 bytes
remote same_location changed to 100 bytes

set_data.coffee的输出

Firebase = require 'firebase'
firebaseUrl = 'https://my_firebase.firebaseio.com/same_location'

ref1 = new Firebase firebaseUrl
ref2 = new Firebase firebaseUrl
ref3 = new Firebase firebaseUrl

ref1.on 'value', (snapshot) -> console.log 'local same_location changed to ' + Buffer.byteLength((snapshot.val() or ''), 'utf8') + ' bytes'

data1 = ''
data2 = ''
data3 = ''
data1 += '1' for i in [1..1000*1000*2]
data2 += '2' for i in [1..1000*1000*3]
data3 += '3' for i in [1..100]

console.log 'data1 ' + Buffer.byteLength(data1, 'utf8') + ' bytes'
console.log 'data2 ' + Buffer.byteLength(data2, 'utf8') + ' bytes'
console.log 'data3 ' + Buffer.byteLength(data3, 'utf8') + ' bytes'

t1 = new Date()
ref1.set data1, (err) ->
  elapsed = new Date().getTime() - t1.getTime()
  console.log 'set1 finished ('+elapsed+'ms) - err is '+err
t2 = new Date()
ref2.set data2, (err) ->
  elapsed = new Date().getTime() - t2.getTime()
  console.log 'set2 finished ('+elapsed+'ms) - err is '+err
t3 = new Date()
ref3.set data3, (err) ->
  elapsed = new Date().getTime() - t3.getTime()
  console.log 'set3 finished ('+elapsed+'ms) - err is '+err

Firebase = require 'firebase'

firebaseUrl = 'https://my_firebase.firebaseio.com/same_location'

ref1 = new Firebase firebaseUrl

ref1.on 'value', (snapshot) -> console.log 'remote same_location changed to ' + Buffer.byteLength((snapshot.val() or ''), 'utf8') + ' bytes'

data1 2000000 bytes
data2 3000000 bytes
data3 100 bytes
local same_location changed to 2000000 bytes
local same_location changed to 3000000 bytes
local same_location changed to 100 bytes
set1 finished (118314ms) - err is null
set2 finished (149844ms) - err is null
set3 finished (149845ms) - err is null

remote same_location changed to 0 bytes
remote same_location changed to 2000000 bytes
remote same_location changed to 3000000 bytes
remote same_location changed to 100 bytes

get_data.coffee的输出

Firebase = require 'firebase'
firebaseUrl = 'https://my_firebase.firebaseio.com/same_location'

ref1 = new Firebase firebaseUrl
ref2 = new Firebase firebaseUrl
ref3 = new Firebase firebaseUrl

ref1.on 'value', (snapshot) -> console.log 'local same_location changed to ' + Buffer.byteLength((snapshot.val() or ''), 'utf8') + ' bytes'

data1 = ''
data2 = ''
data3 = ''
data1 += '1' for i in [1..1000*1000*2]
data2 += '2' for i in [1..1000*1000*3]
data3 += '3' for i in [1..100]

console.log 'data1 ' + Buffer.byteLength(data1, 'utf8') + ' bytes'
console.log 'data2 ' + Buffer.byteLength(data2, 'utf8') + ' bytes'
console.log 'data3 ' + Buffer.byteLength(data3, 'utf8') + ' bytes'

t1 = new Date()
ref1.set data1, (err) ->
  elapsed = new Date().getTime() - t1.getTime()
  console.log 'set1 finished ('+elapsed+'ms) - err is '+err
t2 = new Date()
ref2.set data2, (err) ->
  elapsed = new Date().getTime() - t2.getTime()
  console.log 'set2 finished ('+elapsed+'ms) - err is '+err
t3 = new Date()
ref3.set data3, (err) ->
  elapsed = new Date().getTime() - t3.getTime()
  console.log 'set3 finished ('+elapsed+'ms) - err is '+err

Firebase = require 'firebase'

firebaseUrl = 'https://my_firebase.firebaseio.com/same_location'

ref1 = new Firebase firebaseUrl

ref1.on 'value', (snapshot) -> console.log 'remote same_location changed to ' + Buffer.byteLength((snapshot.val() or ''), 'utf8') + ' bytes'

data1 2000000 bytes
data2 3000000 bytes
data3 100 bytes
local same_location changed to 2000000 bytes
local same_location changed to 3000000 bytes
local same_location changed to 100 bytes
set1 finished (118314ms) - err is null
set2 finished (149844ms) - err is null
set3 finished (149845ms) - err is null

remote same_location changed to 0 bytes
remote same_location changed to 2000000 bytes
remote same_location changed to 3000000 bytes
remote same_location changed to 100 bytes

---

谢谢你的解释，但这并不完全是我想知道的。在我的场景中，同一个客户端开始将文件上载到位置A，在完成之前，他再次将数据上载到同一位置。Firebase将如何处理这种情况？我猜它首先在本地上传，然后再在本地上传。但是两次还没有完成的上传呢？第二个结束的是真实的吗？或者Firebase神奇地知道，在同一个客户端上，总是第二次设置到同一个位置，应该更新数据库我用示例代码OK更新了问题，这确实不同。虽然在服务器上它将是完全相同的，所以仍然没有数据损坏的变化。在客户机上，第二个

集是否会取消第一个集（我认为它不会）。如果在客户机中启用调试日志记录，则可以轻松测试此功能：
Firebase.enableLogging（true，true）请参阅：请记住，Firebase客户端到服务器的通信是连续的（至少在我所知道的任何协议上）。所以它很可能作为选项#3起作用，即使它没有明确定义为那样。但您是否认为，当我在for循环中调用
set
（对于同一个LCO操作）100次时，每一次都会设置大量数据，那么Firebase将依次执行这100次“上载”中的每一次？用例是将文件从目录同步到Firebase-当文件更改时，我调用set（）。在第一次上传完成之前再次提交我的更改。可以只存储关于当前正在与fb同步的文件的信息，并等待它完成—但Firebase可能会开箱即用：）？今天我将测试它并发布我的结果如果100次操作由同一个客户机同步执行，这很可能是真的。但不能保证通过web发送的两个异步事件将以它们启动的相同顺序到达服务器。多个客户端尤其如此，它们不共享套接字连接，Firebase无法优化操作或按特定顺序对其进行排队。是的，但单个fb客户端只是将每个
集
以类似FIFO的队列进行排队，并且每个集在前一个完成后执行。