When stress testing our loadbalancer, i was unable to get more than 20 reliable ssh connections. The following error would be reported.

ssh_exchange_identification: Connection closed by remote host

The resolution for this is quite simple.

Edit the /etc/ssh/sshd_config file and increase the MaxStartups. On my server i set this to 200.

Edit /etc/sysctrl.conf and add the following line:

net.core.netdev_max_backlog = 3000

Then apply this change:

# sysctl -p

 

Recital is a dynamic programming language with an embedded high performance database engine particularly well suited for the development and deployment of high transaction throughput applications.

The Recital database engine is not a standalone process with which the application program communicates. Instead, the Recital database is an integral part of any applications developed in Recital. 

Recital implements most of the SQL-99 standard for SQL, but also provides lower level navigational data access for performing high transaction throughput. It is the choice of the application developer whether to use SQL, navigational data access, or a combination of both depending upon the type of application being developed.

The Recital database engine, although operating as an embedded database in the user process, multiple users and other background processes may access the same data concurrently. Read accesses are satisfied in parallel. Recital uses automatic record level locking when performing database updates. This provides for a high degree of database concurrency and superior application performance and differentiates the Recital database from other embeddable databases such as sqlite that locks the entire database file during writing. 

Key features of the Recital scripting language include:

• High performance database application scripting language
• Modern object-oriented language features
• Easy to learn, easy to use
• Fast, just-in-time compiled
• Loosely-typed
• Garbage collected
• Static arrays, Associative arrays and objects
• Develop desktop or web applications
• Cross-platform support
• Extensive built-in functions
• Superb built-in SQL command integration
• Navigational data access for the most demanding applications
• Scripting  language is upward compatible with FoxPRO

Key features of the Recital database include:

• A broad subset of ANSI SQL 99, as well as extensions
• Cross-platform support
• Stored procedures
• Triggers
• Cursors
• Updatable Views
• System Tables
• Query caching
• Sub-SELECTs (i.e. nested SELECTs)
• Embedded database library
• Fault tolerant clustering support
• Chronological data versioning with database timelines
• Optional DES3 encrypted data
• Hot backup
• Client drivers for ODBC, JDBC and .NET 

Recital 10 enhanced Recital by enabling it to be used in bash shell scripts and in shell commands which use pipes and/or redirect stdin and stdout. If stdin is not redirected then recital will startup and operate as normal in a terminal window. Additionally you can use heredoc to denote a block of recital commands that should be executed. Note that when used in this manner, no UI commands can be executed and no user interaction is allowed.  

# recital < mrprog.prg 
# recital < myprog.prg > myoutput.txt
# recital > myoutput.txt <<END
use customers
list structure
END
# echo "select * from sales!customers where overdue" | recital | wc -l

Individual commands can be executed in shell scripts.

# recital -c "create database sales"
# recital -c "create table sales!invoices (id int, name char(25), due date)"

Expressions can be evaluated and used in shell scripts.

# VER=`recital -e "version(1)"`

You can view what command line options are available by typing:

# recital --help

A quick tip for optimizing TCP performance on linux.

edit /etc/sysctl.conf add the lines:

If using gigabit ethernet:

net.ipv4.tcp_mem= 98304 131072 196608
net.ipv4.tcp_window_scaling=1
net.core.wmem_default = 65536
net.core.rmem_default = 65536
net.core.wmem_max=8388608

To reload these use:

# sysctl -p

If using infiniband:

net.ipv4.tcp_window_scaling=1
net.ipv4.tcp_timestamps=0
net.ipv4.tcp_sack=0
net.ipv4.tcp_rmem=10000000 10000000 10000000
net.ipv4.tcp_wmem=10000000 10000000 10000000
net.ipv4.tcp_mem=10000000 10000000 10000000
net.core.rmem_max=524287
net.core.wmem_max=524287
net.core.rmem_default=524287
net.core.wmem_default=524287
net.core.optmem_max=524287
net.core.netdev_max_backlog=300000