Monday, July 10, 2017

Ethereum mining on AWS

  • Ethereum mining works only on g2.2xlarge or g2.8xlarge instances with Ubuntu 14.04 or later
  • Port 30303 must be opened for both TCP and UDP connections from `anywhere` (in security group settings)
  • Default Ubuntu available with ec2 is minimal i.e. some drm files required for the OS to see GPU drivers are missing. SSH into your machine and run following steps to fix this:
> sudo apt-get install linux-generic  
(Click OK for default option/s when prompted)
> sudo reboot
  • Download CUDA drivers for ec2 instances (use Nvidia units). Working with .deb package (instead of .run) is easier (local or network makes no difference) 
> wget

(Newer versions are available here)

> sudo dpkg -i <cuda repo package>
> sudo apt-get update
> sudo apt-get install cuda
  • Run the following command to check driver is installed: 
> lshw -c video
  • A line that starts with "Configuration:" should mention "...driver=nvidia...", if it doesn't search carefully or try reboot. 
  • If you see "...driver=nouveau..." instead of "...driver=nvidia..." then something is wrong - google how to get rid of it and reinstall cuda.
  • Build geth from source, refer here 
  • run geth to allow it to catch up on the chain: 
> ~/go-ethereum/build/bin/geth
  • install ethminer from cpp-ethereum dev PPAs, refer here 
  • Use following command to check the current hash rate (~6 MH/s) and benchmark ethminer to check that your system is in order: 
> ethminer -G -M 
  • When geth catches up on the blockchain, use the following command to generate a new account: 
> ~/go-ethereum/build/bin/geth account new
  • start geth again with RPC enabled by using command-line below 
> ~/go-ethereum/build/bin/geth --rpc
  • Execute following command to start ethminer
> ethminer -G
  • If using larger g2 instance with 4 GPUs, ethminer needs to be started 4 times. Each time adding a "--opencl-device <0..3>" argument
  • Check logs carefully, ethminer should be getting work packages from geth and be "mining a block"

Sunday, December 27, 2015

How to make YouTube videos run faster

Open Google Chrome
Ctrl + Shift + J - opens Developer Tools, ensure you are on Console tab
On the prompt copy and paste script below:
document.getElementsByTagName("video") [0].playbackRate = 2.5

(Instead of 2.5, one could set any other floating number between 1.00 to 4.00 as the playbackRate)

Saturday, March 21, 2015

Sybase 12.5 to Sybase 15.5 migration - differences that I learnt about

1. Login triggers were introduced in ASE 15.0. A regular ASE stored procedure can automatically executed in background on successful login by any user.

2. Fast bcp is allowed for indexed tables in ASE 15.0.2 and above. bcp works in one of the two modes

  • Slow bcp - logs all the row inserts made, is slower and is used for tables that have one or more index
  • Fast bcp - only page allocations are logged, used for tables without indexes, used when fastest speed possible is required, can be used for tables with non-clustered indexes
3. sp_displaylogin displays when and why a login was locked & also when you last logged in. 

4. Semantic partitions/smart partitioning: ASE 15 makes large databases easy to manage and more efficient by allowing you to divide tables into smaller partitions which can be individually managed. You can run maintenance tasks on selected partitions to avoid slowing overall performance, and queries run faster because ASE 15's smart query optimizer bypasses partitions that don't contain relevant data 

5. With large data sets, filing through a mountain of results data can be difficult. ASE 15's bi-directional scrollable cursors make it convenient to work with large result sets because your application can easily move backward and forward through a result set, one row at a time. This especially helps with Web applications that need to process large result sets but present the user with subsets of those results 

6. Computed columns: Often applications repeat the same calculation over and over for the same report or query. ASE 15 supports both virtual and materialized columns based on server calculations. Columns can be the computed result of other data in the table, saving that result for future repeated queries 

7. Functional indexes: When applications need to search tables based on the result of a function, performance can suffer. Functional indexes allow the server to build indexes on a table based on the result of a function. When repeated searches use that function, the results do not need to be computed from scratch 

8. Plan viewer in the form of a GUI: Plans for solving complicated queries can become very complex and make troubleshooting performance issues difficult. To make debugging queries simpler, ASE 15 provides a graphical query plan viewer that lets you visualize the query solution selected by ASE's optimizer.

9. In ASE 15.0, Update statistics and sp_recompile are not necessary after index rebuild

10. ASE 15 allows to assign two billion logical devices to a single server, with each device up to 4 Tb in size. It supports over 32,767 databases, and the maximum size limit for an individual database is 32 terabytes, extending the maximum storage per ASE server to over 1 million terabytes!

11. As of release 12.5.1, all changes to data cache are dynamic

12. ASE 15.0 and later versions no longer use vdevno. i.e. the disk init syntax doesn't need to mention the vdevno parameter. 

13. Disk init syntax in 12.5 expects size parameter in K, M, and G only. From 15.0 and onwards, T (Terabyte) can be specified. 
Also, pre 15.0; the maximum size of a device was 32GB 

14. The configuration parameter ?default database size? was static in ASE 12. In ASE 12.5, it was made dynamic. 
For ASE 15.0, the below table is specified by Sybase. 
Logical Page Size 2K 4K 8K 16K 
Initial default database size 3MB 4 MB 8 MB 16 MB 
All system tables, initially 1.2 MB 2.4 MB 4.7 MB 9.4 MB

15. The auto database extension was introduced in 12.5.1 and supported later versions.

16. The Dump/Load Database and Dump/Load Tran syntax differ from version and 12.5.2(and hence later versions) (See sybooks for more information. The compression levels 1-9 were introduced.) 

17. ASE and earlier versions used to allow only one tempdb in the server. But all the later versions allow creation of multiple temporary databases. 

18. Before 15.0, after changing a database option we need to use that database and do checkpoint on it. But ASE15.0 doesn't need this. 

19. Restricting proxy authorization is available in 12.5.2 and later releases only. 

20. From version 12.5.2 and onwards, cache creation is made dynamic (sp_cacheconfig [cachename [,"cache_size [P|K|M|G]?] It was static earlier. 

21. Till 12.5.2, backing up a database with password was not possible. ASE 12.5.2 and later allow dump database with passwd. 

22. Cross platform dumps and loads were introduced in ASE 12.5.3 

23. MDA tables (Monitoring and Diagnostic Tables) are available in 12.5.3 and later releases. 

24. Row Level Locking: In ASE 15.0 all the system tables were converted into datarows format.

25. Group By without Order By