parent table struct union vector string enum scalar
root Y Y
table Y Y Y Y Y Y Y
struct Y Y Y
union Y Y
vector Y Y Y Y Y Y

If there is a Y in row A column B, B can be used as a child of A. If it is blank, B is not allowed as a child of A.

Parent root means which type can be used as a root object.

the test schema

Official References

  • Based on Bitcoin
  • PoS overlays upon PoW
  • Add signature algorithms Ed25519 and Schnorr
  • Use BLAKE-256 as hash algorithm
  • Enable segwit to solve transaction malleability
  • Transaction expiration mechanism.

Hybrid Consensus

Decredible | Decred hybrid consensus explained

  • PoW miners propose new block.
  • PoS miners vote whether accepting the block. The ticket should be purchased first. 5 tickets are selected randomly using the new PoW block header. Block is accepted if 3 tickets agree.
  • Block reward is split between PoW and PoS miners.
  • PoS tickets are selected using PoW block header. It guaranteed that is has a very high cost to manipulate picking tickets.

I rarely used more than two marks in Vim, so why not use them as a stack and keep latest history?

The idea is that

  • First shift existing marks in a-y to b-z, thus original mark z is dropped.
  • Then save current position into mark a.
function! PushMark(is_global)
  if a:is_global
    let l:curr = char2nr('Z')
    let l:curr = char2nr('z')
  let l:until = l:curr - 25
  while l:curr > l:until
    call setpos("'" . nr2char(l:curr), getpos("'" . nr2char(l:curr - 1)))
    let l:curr -= 1
  call setpos("'" . nr2char(l:curr), getpos("."))

" Push to marks a-z
nnoremap <silent> m, :call PushMark(0)<CR>
" Push to marks A-Z
nnoremap <silent> m. :call PushMark(1)<CR>

I recently worked in a Ruby on Rails project which should integrate with many different payment systems. There system mostly use RSA in encryption and signature. However they provide the RSA keys in different formats, it is a challenge to choose a right way to read the keys in Ruby.

RSA is an asymmetric cryptographic algorithm, thus it requires two keys, private key and public key. The key itself is just binary, but it can be encoded in different format.

Just upgraded Graylog to cluster in a project. Because syslog UDP is used as input, a UDP load balance is required to distribute logs to servers in the cluster. Since the servers are hosted in Aliyun, I tried Aliyun UDP Load Balance first. But it does not forward requests evenly, and health detection diagram cannot be disabled. The popular HTTP load balance tool HAProxy does not support UDP. Fortunately, Nginx can be used as a UDP load balance.

It is common to use Redis as read buffer。To read data, first check whether it exists in Redis. If so, use the cached data, otherwise read from the backend storage and save a copy into Redis. To write data, first save into backend storage, then clear or update Reids cache.

But if the system bottleneck is in writing, the solution above does not work. But it is easy to modify it into a write buffer.

  • Read: Check whether the data exists in Redis. Read from backend storage if not.
  • Write: Just write into Redis. Notify background worker via message queue to flush the cache into backend storage.
  • The background worker watches message queue, save data and delete from Redis.

The message queue can be implemented using Redis LIST. Official RPOPLPUSH – Redis command document already described how to implement a reliable queue. The remaining issue is how to safely delete saved data from Redis.

  • Add properties files into src/main/resources
  • Global messages location:
    • src/main/resources/ is for default locale
    • src/main/resources/ is for locale en_US
  • Resource Bundle for component: Same directory structure to the class path. For example the resource bundle file for views.Main can be found in src/main/resources/views/, or file name for specific locale.
  • Enable native-to-ascii conversion in IntelliJ to ease editing UTF-8 values.

I have wrote many scripts to automate the work in macOS. This one is the most freqently used one. The script can capture the current selection in frontend most app in OmniFocus, and I can jump back to the app using URL.

Vcpkg is a tool published by Microsoft, which is used to manage C/C++ libraries in Windows. It makes libraries installation easier, and it works well with CMake.

But it is not straitforward to staticly link the depdendent libraries using vcpkg.

Concourse CI is an awesome open source continuous integration tool. If you are not using Gitlab, and want to setup a CI server, it is a good choice.

Concourse CI provides Docker image and docker compose sample config. But when I run the hello world example, I have met several problems.