RAIB

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(c) '2007-2008 by Andreas Filsinger

Redundant Array of Independent dataBases

The goal of RAIB (for firebird 3.0?!) is to ensure the availability of a firebird database - even if hardware fails. This is done by fail-over servers (spares) or Log-Packets (.flog File) on a remote Filesystem. In other Environments (without RAIB) you loose all Data from the Moment of your last Backup until the Moment of faliure. With RAIB you are able to get your Database up to the state where it was. This is just a concept - BUT implementing this ideas will make firebird 3.0 (with the vulcan engine) unbreakable.
Remember that malfunction of a single transistor in your high-end-server will bring firebird down (And modern servers have millions of it). Maybe your HD is OK, or you trust on a RAID 5 Storage. But the Question is: How long does it take to get the firebird-service online again!
With RAIB you can immediatly connect your application to a spare-Host after the failure. In this Moment you are restricted to "read-only" if you reduce to "read only" SQL-Statements, a admin can switch one spare to the master mode, so all the functionality of the firebird database can be used.

How it will work

The work is done by 8 (new?) techniques, not yet implemented in firebird:

  1. Statement-Classification: by evaluating and executing a statement it is classified as a "R"- "W"- or "I"-Statement.
  2. Heart-Beat-Sequence: a BIGINT living inside the database, counts the impacts to the database since the Statement "CREATE DATABASE". This will help naming Statement-Log-Packets
  3. Statement-Order: A single Instance that decides in wich order the incoming Statements are executet. Inside a time window, this instance is free to do this ordering, but the order MUST be logged.
  4. Statement-Packets-Logger: Logs DDL/DML "W"-Statements in a way so they can build basis of a Statement - "playback".
  5. snap-shot-backups: a Backup-Mode where all the impact AFTER the Backups was started are invisible to the Backup.
  6. Statement-Playback: a system where server can execute "Statement-Packets".
  7. Playback-Mode: gbak sets a database in this mode when doing statement Playback to a database.
  8. Deterministic SQL: all Statements MUST end in computable results, so they can be executed in a server-swarm

Heart-Beat-Sequence

SEQ_HEART_BEAT

A Database has an internal SEQUENCE (GENERATOR) (the Heart-Beat-Sequence = HBS [BIGINT]) that is incremented after each W-Statement commit doing some change to data or metadata. A read-Only Statement (I/R) should not incrememt the HBT.

Serialize

The master must have a mechanism to force quasi parallel W-Statements in an serialized order. The assigned HBS Value will make clear in wich order the statements are executed. Long time conspumting statements are not a problem because a W-Statement with HBS = n, only sees the Database in the Snap-Shop State n-1.

Statement Classification

firebird executes SQL-Code like "DROP TABLE SAMPLE" or Service Requests like "BACKUP DATABASE". If we want something like a spare-server we should filter the requests that really do some change to the Database. The three classes are "W"rite / "R"ead and "I"nformal.

"W" Requests

"R" Requests

"I" Requests

Samples
Client-Request: DROP TABLE CLUB$2873
Server-Classification: "W" / SEQ_HEART_BEAT=928372

Client-Request: SELECT CURRENT_TIMESTAMP from RDB$DATABASE
Server-Classification: "I"

Client-Request: SELECT COUNT(RID) from HUGETABLE
Server-Classification: R

Deterministic SQL

a quest to impact that a Statement do to the Database, that it will have the same result independant when where and why executed. Forbidden are Sideeffekts like "CURRENT_TIMESTAMP", "RAND()", results of USER Tabels or PERFORMANCE Tables or Logik that depends on Bits that are Outside the Database itself.

Why do we need this:

  1. Because of relyable playbacks.
  2. Because of an exetuting swarm, resulting in a 100% identical database

GID

as a "changed" marker

The GID is a global int64 Sequence (Generator) and a "implizit" Field in every DB-Table wich mark or tag Records, Tables, Views and the Database itself. By now there are no arguments for having a GID Granularity set to Field-Level.

  • Every Time a "w" statement was completed, the Database GID gets incremented. You can read the actual GID by
select GID from RDB$DATABASE
  • Also this new GID Value is store to the affecte TABLE(s). You can read this.
select GID from TABLE1 

// seems the same like
select MAX(GID) from TABLE1
  • Every Record holds its GID
 // get the actual GID of a record
 select GID from TABLE1 where RID=2029382
 
 // get all the record, sorted by modification order, newest first
 select * from TABLE1 order by GID descending, RID ascending


as the only valid Reference

STOP! Do not mix up RID and GID sequence. Think about a global RID pool! New inserted Records get their (first) RID from the GID

Update a Record: if unchanged

sometimes Applications or users need long time to "change" a record. At "first" the Applications read all Record-Data from Db-Table. Then after 5 Minutes they post their changed Record-Fields by a update statement. If the Data-Mask is complex, than even more TABLES may be affected by the update. If the application not only read the REcord-Data but also read the GID, it can post an update "on the knowledge state of 8383892". If the knowledge-Sate has gone further, the update will fail - the user may be informed that the unlying data has changed in the meantime and the update is not possible by know. The App may present a diff of the "local" and new "remote" Record - let the user decide how the merge could look like. 

update TABLE1 set
 FIELD1 = NewValue
where
 (RID=828273) and
 (GID=8383892)

if "affected rows" = 0 RID is gone or GID is changed.

Statement-Log-Packets

A SQL-Statement like "DROP TABLE HUGEONE" may purge thousands of Pages of the Database File, and modify 1 or 2. The Log-Packet itself schould NOT contain all the changed Database Pages or such low-level Details but the SQL-Statement itself. We can trust on the fact that the spares have all the knowledge to understand the Statement and execute it exactly like the master. This information is transmitted to one or more spares. This information is also stored in the Database itself for a time (not part of a backup). At least until its prooven that a n.fabk is available. After the Log-DataBlock must succsessfully

  1. Do the Statement, detect while doing it, if it is harmfull to the Database (W oder R)
  2. if W: compile a log-block with the name GEN_ID(HBT,1); if R: break
  3. Send the LOG over the line.


Generating a LOG-Packet

"R"-Statements /"W"-Statements

Each Request, on its way through the Database holds a Flag, saying "I am Read/Only" or "I did some impact" to the Database. This Flag (the R/W-Flag) is set by the engine in the actual context, because you can formulate a statement wich is 99% a "R"-one, but there comes a day, this statement do a change to the Database. When the engine detects a change to Data or Metadata it sets the "Write"-Flag, this statement was prooven now to have a impact to the database, it is a "W"-Statement and must at its End increment the SEQ_HEART_BEAT and a Statement-Log is written.

The Log-Packet is assembled by the engine step by step right in the moment by parsing and executing it. The LOG-Packet is the "compiled" version of the Statement. The LOG-Paket is written to a memory block. If a "W" Statement reads CURRENT_TIMESTAMP (Timestamp) or RND (Randomize) a copy of the returned value MUST be stored in the LOG, because the spares can not trust on own values. If a Request is fully executed, and the engine didn't set the "W"-Flag - the LOG-Packet is purged, because it did no harm to the database it can say us nothing about history. Else (a "W"-Statement) the Packet is populatetd to the spares. The server itself hold a persistent copy of the Log-Packet to help spare get up to date if they missed something. Only a successfull backup can delete the Log-Packets that are generated before the .fbak HBS.

Quasi "W" Statements 

select CURRENT_TIMESTAMP from RDB$DATABASE

is a "W"-Statement that can only be executed by the master, because the client ask for information that is NOT part of the Database itself. So all external Information going throgh the engine are Quasi-"W" (user account infos, or coming user SQL Statements). They MUST be executed by the master, but do NOT goto the Log.

Statement

UPDATE PERSON SET MOMENT = CURRENT_TIMESTAMP WHERE LOAN = RND(2920)

Log-Paket

P:RND=2093 P:CURRENT_TIMESTAMP P:CURRENT_TIMESTAMP P:CURRENT_TIMESTAMP S:UPDATE PERSON ...

Snap-Shot-Backups

Statement-Playback

Database in spare mode

  • the LOG-Receive Thread

the master initiates communication to a spare and post LOG Packets to the spare. Alle Packets are flushed into memory - if CRC is ok, the spare sends a ACK to the master. The master do NOT wait until the spare executes the statement because the master already prooved that the statement is executable.

  • the Worker-Thread

read the LOG-Packets, and execute it against the own Database.

  • LOG-missed

if the spare was offline a time, she sees that local.HBT <> LOG.HBT+1. Before it can execute actual LOG-Packets she MUST ask the master (or other spares) for the missing LOG Packets. After doing the old stuff it can start to do execute the actual receiced LOG-Packtes. While this time, the log-Receive thread isnt stopping filling the LOG-Buffer.


Playback-Mode

The Playback-Mode (or Spare Mode) of a database is a new type of Database "Shutdown" Mode. Connections to this host in Spare Mode see no difference to a normal Database. work normal but refuse "W" Statement with a special error message. They may redirekted to a master.

be a local spare

the master writes the LOG-Packets (FileName <HBT>.flog) to a (remote) filesystem.

be a cold spare

a firebird-server receives the log-Packets but do not execute them. The worker-Thread writes the .flog Files to the filesystem if the system is idle.

be a hot spare

a firebird-server receives and execute the log-Packets a fast as possible.

be a master


planned switiching the role from master to spare

  1. the master do not accept W Statements any more. (Try again in 2 Minutes!)
  2. the master ensures that one spare is ready to take over (master.HTB=spare.HTB)
  3. the master switch to "spare" Mode
  4. the spare switch to "master" Mode

Database in master mode

no limitations. He must bring the Log-Packets to the world:

  • By UDP to the spares.
  • By fopen to the filesystem.
  • By move to the memory.

(add a ) RDB$Cluster Table

inside the database is the information about the spares and the master. 

IP               Role       last-HBT
192.168.115.192  master
192.168.115.196  spare
192.168.115.80   spare
30.23.12.3       spare


detecting the failure

  • Master is Not Responding
  • Spare say they have problems executing crazy Packets.

Positive Side Effekts

if a client assumes that a special statement is "R" AND HBT of a spare is the HBT of the master she can post this statement to a spare to take load away from the master. The spare will bring the same result as the master.

Communication master<->spare

if a spare comes up (on connection request of a master), a spare can ask the master how

Good to have several spares

it is enough fore the master to have only one responding spare. If a connection to a spare fails the master retries it every 20 Seconds.


Restore Szenario

  1. restore the database from a .fbak
  2. read the value of GEN_HBT
  3. let the server execute all *.flog Files beginning from GEN_HBT+1


New ERROR Messages

"W"-Statement not allowed on a spare

the client must understand a new error-Msg when trying to place a statement to a spare that was a master before. the client must interrpret the new connection string and (re)prepare a open statements.

  1. Error-Msg with a Retry-Option: "Im a Spare, please retry with [%server:%database]"


Failed to Log your Statement

if the master can not log the statement to any spare this error MSG is generated.

the lying master concept

Imaging a host wich is a spare (in truth) and tells the world that she is a Master. This is a spare wich executes all the "R" Statement, but automatically routes "W"-Statements to a master without telling the connection something about it. The result is routed back to the connection AFTER she has executed the Log-Packet, so that this spare is "true" wich its single connection. There may be a "gab" of Log-Packets (more to come here).
You may have a Grid of "lying masters" in a webshop scenario. Alle the "W" Work is done by one hidden master, not slowed down by anoing "R" Statements of any connection.

the lazy worker

  • say "Im done" if all checks are done that ensure "T" will succseed, but dont do the work!

the Cash Assoziator

  • Cashing: is a technique that repeats a saved answer to an known question without "understanding" the question again. This is Quick!
  • Trick 1: Always use cash if since last "R" there was no "T"
  • Trick 2: On first insert in cash, build a dependecy-tree, on what the Answers depends on, if asked again, only check tree, if not more developed than the saved version -> use cashed answer
  • Hint: While executing "W" Statement cut Cache-trees
  • Trick 3: Cash-Questions are parallel to Answers, we have an unlimited Count of CPUs.

the Context Bubble

  • repesents the Dependecy Tree

A cash Element contains the "cas-Azzoziator-ID" the "Answer" the "Context-Bubble". In "idle" Time the Cash is cleared off all the Entries wich Context-Bubbles blobs. A "R" Statement can be cashed if "Context" Bubble still is alive

the new I/O Model: IO+C (Input Output Cacheable)

  • extends the classic I/O Modell by the possibility to Ask the I for a List of dependencies of the I
Q:"select SUM(BETRAG) FROM KOSTEN where Cond" into Cache
A:20,00 Euro (=Cache Identifier 261526271)
Qa:"select SUM(BETRAG) FROM KOSTEN where Cond" from Cache
Qb:Cache 261526271 still valid?
Aa:Cache 261526271 !if unchanged!
Ab:20,01 Euro (=Cache Identifier 261526272) !if changed!

Club-Pages

"Ich hab schon mal auf einer Grafik gesehen, dass die Index-Values mit Duplikationen irgendwie mit in dem Suchbaum gespeichert sind, ich denke das hat traditionelle Gründe. Die richtige Implementierung ist es, nur die distinct Werte der Index-Values genau einmal zu speichern, jeder Index-Value sollte dann auf eine Mitgliederliste verweisen. Die Null Values gehören nicht in den Suchbaum und sollten die Index-Performanche nicht beinflussen, sie gehören in die Mitgliederliste "NULL". "

Club Pages are Record-Reference Index-Pages telling if a Record is Part of a Club or not. Updating a Record may corse a "enter" oder "leave" club event. Delete is a "leave" is it was a memeber. Insert may be "enter". A "Club" is defined by Club-Rules this may be 

(INCOME>10.000)

or

(RID<>MASTER_R>


Clubs speed up OLAP because if a Statement "where" Condition match a Club-Rule. 

join CLUB$$INCOME on
 (PERSON.RID=CLUB$$INCOME.PERSON_R)

Project names alternatives

Firebirdie from "firebird D", "D" for Deterministic Mode


GenerationsCount: SQL Statement, das mich dazu gemacht hat.

Links

http://www.linbit.com/

granid

// a simple artefact was found in space // just a small stone // a texture like granit // a first it seems like rauschen // than a set of algorithems // where extracted by the intelligence // // i am granid. a database server. i am open source // // several elements mixed up // by one spirit // one force arranged granulat // big pressure, fire and heat // then - silence - one piece // a stone was born // // performance, stability, transparence // no past, only the future // no limitations, only the chanche to make it faster // // ANFICO - The Language Extender // BLAGER - The Binary Lager // D64 - 64 Bit Data-Manager // // // Data: <UInt32 TimeStamp> <UInt64 RecordChangeTag> // //

Neu: CLUB

In Zukunft sollen Parameter Eingabedialoge abfragbar sein. (Ev. mit Historie und default Belegungen)

In Zukunft sollen Dimensionen vordefiniert sein (Artikel,Belege, Verkäufe, Personen).

In Zukunft sollen Attribute angebbar sein (Artikel.Anlage > -3 Monate, Person.Alter > 40).

In Zukunft sollen Betriebsbegriffe vordefinierbar sein.
Umsatz(eines Artikel) (select MENGE_GELIEFERT from POSTEN-Club)
Umsatz(einer Person) (select DAVON_BEZAHLT from BELEG-Club)

der POSTEN-Club kann dann einfach * sein, oder wieder selektiert. n-Idee: Jede Dimension hat üben, in die manden Abfrage-Faden flechten kann. OLAP-Admins definieren Clubs, Dimensionen und en. Zeiträume sollten nun (Jahrgenauer |Taggenauer | Monatgenauer | Wochengenauer) kummuliert werden. Das ist die Granularität Summe ist die größe Körnung. 

Club: A (maybe empty) List of Members
Rule: A piece of deterministic logical code that decides, if a record is a Member or not. Club uses Rules to define if one is  a member or not.
Mem ber: A Record that is a part of one ore more clubs
isMember(): Answer the Question if a En
Field: space in a Record that can store a value , or can be empty
Record: One Line in a Table
Table: The Collection of Lines
Welcome: Somewhat happend, you are now gain membership of a club
Dependencies: A stored hint, that the system has to check again some rules to say welcome or good bye
transformer: a piece of code that calculates a in64 from a key of 
Transaction: a of atoms
atom: a single changing operation done to the base

Neu: Begriff

Begriffe wie "Kunde" und "Umsatz" oder "Sortimentsbewegung" werden als OLAP-Statements definiert. Ein zentrale OLAP Abfrage könnte nun Fragestellungen mit Hilfe von "Begriffen" formulieren. Beispiel:

  • Alle Kunden mit Sortimentsbewegung in den Sortimenten "A" und "B" im Zeitraum Januar bis März 2010

Die Auflösung würde so erfolgen, dass zunächst die Begriffe 

# 1. Schritt: Begriffstabellen bilden
Kunden('01.01.2010','31.03.2010')
Sortimentsbewegung('01.01.2010','31.03.2010')

ausgelöst werden. Diese Begriffs-Eregbnise werden in temporären Ergebnistabelle zuwischengespeichert. Alles über EIN zentrales online SQL-Statement lösen zu wollen hat sich als unwirtschaftlich herausgestellt. 

# 2. Schritt 
select PERSON_R from Kunden
join Sortimentsbewegung where
(Kunden.PERSON_R=Sortimentsbewegung.PERSON_R) and
(
 (Sortimentsbewegung.SORTIMENT_R='A') or
 (Sortimentsbewegung.SORTIMENT_R='B') or
)

würde man bei firebird alles in eine gemeinsame Transaktion packen, so könnte man "CREATE GLOBAL TEMPORARY TABLE ON COMMIT DELETE" machen.

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