Using Lua for Stored Procedures in a High Availability Database

VeriSign I2S Team

Name of Presenter: John Rodriguez

Date: July 14, 2008

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Agenda

1 VeriSign High Availability Database Background (VHAD) –

Simplicity

2 Why Choose Lua for Stored Procedures?

3 VHAD Integrated Development Environment – IDE

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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, memory-

based 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?▪ Carefully, aggressively simplify the design and architecture.▪ Target only the critical subset of system functionality.

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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.

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+ 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, ormust 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.

Running Continuously

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Continuous Availability

+ Commercial Availability - routine outages▪ 90% 2 hours down/day - nightly batch jobs ▪ 99% 1 hour down/week - weekly backups▪ 99.9% 1 hour down/month - monthly reorganization

+ High Availability - occasional outages▪ 99.95% 1 hour down/quarter - quarterly upgrade▪ 99.99% 1 hour down/year - reboot after failure,

+ Continuous Availability - no scheduled outages▪ 99.999%5 minutes down/year - automated switch over

99.9995% 2 minutes down/year - Project Goal99.9999% 30 seconds down/year - Wow

+ Perfect Availability - no visible failures▪ 99.99999% failure is never visible to work in progress

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Topology

Prime processes changesand manages data consistency+ 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.▪ Protects against poison data.▪ Not subject to errors in the

database logic.

+ Replicas support massiveread-only access.▪ Replicas don’t vote, which

simplifies recovery analysis.▪ Replicas can be promoted to

Mirror when needed.

Prime

Guard

ReplicaReplica

Mirror MirrorMirror

ReplicaReplica

Replicassupport

unlimitedread access

Mirrorsconfirm

persistence

Guard defends against poison data

As many levels as desired

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Agenda

1 VeriSign High Availability Database Background (VHAD) – Simplicity

2 Why Choose Lua for Stored Procedures?

3 VHAD Integrated Development Environment – IDE

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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.

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Cursor Example – The Schema in SQL

+ Assume there is a database table like the following:▪ CREATE TABLE DOMAIN_T (

DOMAINNAME VARCHAR(256), REGISTRAR VARCHAR(256), DATE TIMESTAMP);

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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)

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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.DOMAINNAMEdomain.RESISTRAR = args.REGISTRARdomain.DATE = args.DATECursor.insert(domain)commit()

end

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Agenda

VeriSign High Availability Database (VHAD) Background – Simplicity

Why Choose Lua for Stored Procedures?

VHAD Integrated Development Environment – IDE

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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!

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ldb

+ Developed a command line Lua debugger - ldb

+ The ldb language▪ list firstline [lastline]▪ break line ▪ clear line ▪ display [varname] ▪ step ▪ continue ▪ print stack|trace|breakpoints ▪ quit ▪ help

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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

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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

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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.

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Questions + Answers

Thank You

"Make everything as simple as possible, but not simpler." Albert Einstein