Using Lua for Stored Procedures in a
High Availability Database
VeriSign I2S Team
Name of Presenter: John Rodriguez
Date: July 14, 2008
Agenda
1 VeriSign High Availability Database Background (VHAD) –
Simplicity
2 Why Choose Lua for Stored Procedures?
3 VHAD Integrated Development Environment – IDE
2
Introduction
+ VeriSign’s mission is making the Internet and telecommunications networks
more reliable, more intelligent, and more secure.
+ VeriSign runs the registry (database) for the .com, .net, .cc, and .tv TLDs.
+ The motivation for VHAD was driven by historic and projected transactional
growth and system availability requirements
+ VHAD is a very high availability (99.9995%), very fast, replicated, memorybased database, optimized for Online Transaction Processing (OLTP).
+ Are you crazy? Why write your own database?
▪
▪
Big, replicated commercial database systems just have too many moving parts.
Cost rises exponentially when we push well beyond normal availability levels.
+ I still think you’re crazy. What makes you think you can actually do this?
▪
▪
3
Carefully, aggressively simplify the design and architecture.
Target only the critical subset of system functionality.
Mission
+ Continuous Availability
▪
Availability is achieved by minimal administration, narrowly focused
scope, simple and clear design, in-memory architecture
▪ Approach is NOT added redundancy over a lower-availability database.
+ High Performance
▪
Designed for 1+ billion update transactions per day (~ 50K/second).
▪ Designed for an unlimited volume of read-only transactions.
+ Online Transaction Processing
▪
Assumes Insertion/Update of approximately 10 rows per transaction.
▪ Not designed for general purpose set processing – no huge transactions.
+ Storage Engine is fully ACID compliant
Atomicity – Transactional commit/abort – all or nothing.
▪ Consistency – Foreign key / uniqueness relationships are enforced.
▪ Isolation – A transaction never sees someone else’s partial change.
▪ Durability – Acknowledgement of a commit guarantees data persistence.
▪
4
Running Continuously
+ What kinds of things don’t stop but just keep going, going, going…?
▪
The moon keeps orbiting.
▪ Simple tools just work.
▪ What makes them different
from things that break, or
must be stopped occasionally?
+ Continuous Availability:
No “maintenance windows”, no fine print.
▪ No excuses, it doesn’t matter why.
▪ Not an affirmation that we will fix it,
but a guarantee that we won’t need to.
▪
+ How targeting really high availability effects design choices.
5
Continuous Availability
+ Commercial Availability
▪
▪
▪
90%
99%
99.9%
2 hours down/day
1 hour down/week
1 hour down/month
+ High Availability
▪
▪
99.95%
99.99%
▪
6
- quarterly upgrade
- reboot after failure,
- no scheduled outages
99.999% 5 minutes down/year
99.9995% 2 minutes down/year
99.9999% 30 seconds down/year
+ Perfect Availability
- nightly batch jobs
- weekly backups
- monthly reorganization
- occasional outages
1 hour down/quarter
1 hour down/year
+ Continuous Availability
▪
- routine outages
- automated switch over
- Project Goal
- Wow
- no visible failures
99.99999% failure is never visible to work in progress
Topology
+ Prime performs all changes.
▪
If the Prime fails, a Mirror is
automatically selected to be
promoted to Prime .
+ Mirrors confirm persistence.
▪
▪
Provide persistence in memory.
Must include a separate site.
+ Guard only writes log to disk.
▪
▪
▪
7
Mirrors
confirm
persistence
Guard defends
against poison data
Prime
Guard
Mirror
Mirror
Mirror
Protects against poison data.
Not subject to errors in the
database logic.
+ Replicas support massive
read-only access.
▪
Prime processes changes
and manages data consistency
Replicas don’t vote, which
simplifies recovery analysis.
Replicas can be promoted to
Mirror when needed.
Replicas
support
unlimited
read access
Replica
Replica
As many
levels as
desired
Replica
Replica
Agenda
1 VeriSign High Availability Database Background (VHAD) – Simplicity
2 Why Choose Lua for Stored Procedures?
3 VHAD Integrated Development Environment – IDE
8
Rationale for Choosing Lua for Stored Procedures
+ Lua shares major VHAD design principle – keep it small and simple.
+ Lua is mature and very stable – critical core code is not expanding.
+ Most databases realistically require a service outage when a stored
procedure is added or modified, and that change isn’t transactional.
+ VHAD requires more dynamic behavior there, because anything that
compromises even a single transaction is considered an outage.
+ Lua gives us the dynamic behavior we need – different interpreters
can have different code in use simultaneously for a procedure name.
+ Highly parallel operation is needed: thousands of threads at once –
Lua interpreter is fully thread safe and reentrant, unlike most others.
+ Lua Garbage Collection via interpreter heap – it’s a huge advantage
not to have to explicitly deallocate or use reference counts.
+ Efficient direct access to C++ objects gives a big speed advantage.
9
Cursor Example – The Schema in SQL
+ Assume there is a database table like the following:
▪
10
CREATE TABLE DOMAIN_T (
DOMAINNAME
VARCHAR(256),
REGISTRAR
VARCHAR(256),
DATE
TIMESTAMP
);
Cursor Example – Userdata and Metatable
+ One of the basic types that Lua supports is userdata.
+ Lua provides APIs to create userdata types and associate a
metatable of metamethods to a userdata type:
▪
Static const struct luaL_reg cursor_metatable[] = {
{“__newindex”, setColumn},
{“__index”, getColumn},
{“__gc”, cleanup},
{NULL, NULL}
}
▪ luaL_newmetatable(lstate, “Session.Cursor”)
▪ luaL_register(lstate, NULL, cursor_metatable)
+ Associating metamethods to userdata:
▪
luaL_getmetatable(lstate, “Session.Cursor”)
▪ Lua_setmetatable(lstate, -2)
11
Cursor Example - Lua Stored Procedure
+ A sample metamethod in C:
int setColumn (lua_state *lstate) {
luaL_checkudata(lstate, 1, “Session.Cursor”)
colName = lua_tostring(lstate, 2)
colData = lua_tonumber(lstate, 3)
}
+ A sample stored procedure that uses the Cursor type:
function INSERT_DOMAIN (args)
domain
= Cursor.new (“REGY”,
“DOMAIN”)
domain.DOMAINNAME
= args.DOMAINNAME
domain.RESISTRAR
= args.REGISTRAR
domain.DATE
= args.DATE
Cursor.insert(domain)
commit()
end
12
Agenda
VeriSign High Availability Database (VHAD) Background – Simplicity
Why Choose Lua for Stored Procedures?
VHAD Integrated Development Environment – IDE
13
VHAD Integrated Development Environment - IDE
+ Need an environment that lets a user:
▪
▪
▪
▪
▪
Write a stored procedure
Load a stored procedure dynamically
Debug a stored procedure
List schemas, tables, column values, etc.
Rapid prototyping of stored procedures
+ Developing a database tool like sqlplus – but better
▪
Display schemas, stored procedures, etc.
▪ Display columnar data
▪ Execute a stored procedure
▪ Sqlplus does not have a stored procedure debugger!
14
ldb
+ Developed a command line Lua debugger - ldb
+ The ldb language
▪
▪
▪
▪
▪
▪
▪
▪
▪
15
list firstline [lastline]
break line
clear line
display [varname]
step
continue
print stack|trace|breakpoints
quit
help
ldb Example
ldb> break 11
setting breakpoint at ./sort.lua line 11
11 local i=l+1
ldb> continue
original
Jan,Feb,Mar,Apr,May,Jun,Jul,Aug,Sep,Oct,Nov,Dec
stopping at breakpoint in ./sort.lua line 11
11 local i=l+1
ldb> display m
Find local name m:
name m, type number, value 1.000000
Find global m:
Did not find global m
16
ldb Example - continued
ldb> print stack
7: 2
6:`Jan'
5: 1
4: function
3: 12
2: 1
1: table
ldb> print trace
level# name,type,language,source,currentline,linedefinedat
0# qsort,global,Lua,./sort.lua,12,5
1# testsorts,global,Lua,./sort.lua,55,51
2# ,,main,./sort.lua,66,0
17
Conclusion – Difficulties Faced
+ Execution of stored procedures from memory.
+ Thread pools of Lua_states are reused.
+ Decimal adaptation and other numeric types.
+ Debugging stored procedures.
18
Questions + Answers
19
Thank You
"Make everything as simple as possible, but not simpler."
Albert Einstein