rdelaage
/
postgresql
mirror of https://git.postgresql.org/git/postgresql.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

Update replication todo.

This commit is contained in:
Bruce Momjian 2000-06-01 19:46:29 +00:00
parent 49ee133424
commit 2b0956e783
3 changed files with 914 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
doc/TODO
View File

@ -155,7 +155,7 @@ EXOTIC FEATURES
* Add sql3 recursive unions
* Add the concept of dataspaces
* Add replication of distributed databases
* Add replication of distributed databases [replication]
* Allow queries across multiple databases
* Allow nested transactions (Vadim)
@ -198,7 +198,7 @@ FSYNC
INDEXES
* Use indexes in ORDER BY for min(), max()
* Use indexes to find min() and max()
* Use index to restrict rows returned by multi-key index when used with
non-consecutive keys or OR clauses, so fewer heap accesses
* Allow SELECT * FROM tab WHERE int2col = 4 use int2col index, int8,

907
doc/TODO.detail/replication Normal file
View File

@ -0,0 +1,907 @@
From goran@kirra.net Mon Dec 20 14:30:54 1999
Received: from villa.bildbasen.se (villa.bildbasen.se [193.45.225.97])
by candle.pha.pa.us (8.9.0/8.9.0) with SMTP id PAA29058
for <pgman@candle.pha.pa.us>; Mon, 20 Dec 1999 15:30:17 -0500 (EST)
Received: (qmail 2485 invoked from network); 20 Dec 1999 20:29:53 -0000
Received: from a112.dial.kiruna.se (HELO kirra.net) (193.45.238.12)
by villa.bildbasen.se with SMTP; 20 Dec 1999 20:29:53 -0000
Sender: goran
Message-ID: <385E9192.226CC37D@kirra.net>
Date: Mon, 20 Dec 1999 21:29:06 +0100
From: Goran Thyni <goran@kirra.net>
Organization: kirra.net
X-Mailer: Mozilla 4.6 [en] (X11; U; Linux 2.2.13 i586)
X-Accept-Language: sv, en
MIME-Version: 1.0
To: Bruce Momjian <pgman@candle.pha.pa.us>
CC: "neil d. quiogue" <nquiogue@ieee.org>,
PostgreSQL-development <pgsql-hackers@postgreSQL.org>
Subject: Re: [HACKERS] Re: QUESTION: Replication
References: <199912201508.KAA20572@candle.pha.pa.us>
Content-Type: text/plain; charset=iso-8859-1
Content-Transfer-Encoding: 8bit
Status: OR
Bruce Momjian wrote:
> We need major work in this area, or at least a plan and an FAQ item.
> We are getting major questions on this, and I don't know enough even to
> make an FAQ item telling people their options.
My 2 cents, or 2 ören since I'm a Swede, on this:
It is pretty simple to build a replication with pg_dump, transfer,
empty replic and reload.
But if we want "live replicas" we better base our efforts on a
mechanism using WAL-logs to rollforward the replicas.
regards,
-----------------
Göran Thyni
On quiet nights you can hear Windows NT reboot!
From owner-pgsql-hackers@hub.org Fri Dec 24 10:01:18 1999
Received: from renoir.op.net (root@renoir.op.net [207.29.195.4])
by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id LAA11295
for <pgman@candle.pha.pa.us>; Fri, 24 Dec 1999 11:01:17 -0500 (EST)
Received: from hub.org (hub.org [216.126.84.1]) by renoir.op.net (o1/$Revision: 1.1 $) with ESMTP id KAA20310 for <pgman@candle.pha.pa.us>; Fri, 24 Dec 1999 10:39:18 -0500 (EST)
Received: from localhost (majordom@localhost)
by hub.org (8.9.3/8.9.3) with SMTP id KAA61760;
Fri, 24 Dec 1999 10:31:13 -0500 (EST)
(envelope-from owner-pgsql-hackers)
Received: by hub.org (bulk_mailer v1.5); Fri, 24 Dec 1999 10:30:48 -0500
Received: (from majordom@localhost)
by hub.org (8.9.3/8.9.3) id KAA58879
for pgsql-hackers-outgoing; Fri, 24 Dec 1999 10:29:51 -0500 (EST)
(envelope-from owner-pgsql-hackers@postgreSQL.org)
Received: from bocs170n.black-oak.COM ([38.149.137.131])
by hub.org (8.9.3/8.9.3) with ESMTP id KAA58795
for <pgsql-hackers@postgreSQL.org>; Fri, 24 Dec 1999 10:29:00 -0500 (EST)
(envelope-from DWalker@black-oak.com)
From: DWalker@black-oak.com
To: pgsql-hackers@postgreSQL.org
Subject: [HACKERS] database replication
Date: Fri, 24 Dec 1999 10:27:59 -0500
Message-ID: <OFD38C9424.B391F434-ON85256851.0054F41A@black-oak.COM>
X-Priority: 3 (Normal)
X-MIMETrack: Serialize by Router on notes01n/BOCS(Release 5.0.1|July 16, 1999) at 12/24/99
10:28:01 AM
MIME-Version: 1.0
MIME-Version: 1.0
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable
Sender: owner-pgsql-hackers@postgreSQL.org
Status: OR
<P>I've been toying with the idea of implementing database replication for =
the last few days. &nbsp;The system I'm proposing will be a seperate progra=
m which can be run on any machine and will most likely be implemented in Py=
thon. &nbsp;What I'm looking for at this point are gaping holes in my think=
ing/logic/etc. &nbsp;Here's what I'm thinking...</P><P>&nbsp;</P><P>1) I wa=
nt to make this program an additional layer over PostgreSQL. &nbsp;I really=
don't want to hack server code if I can get away with it. &nbsp;At this po=
int I don't feel I need to.</P><P>2) The replication system will need to ad=
d at least one field to each table in each database that needs to be replic=
ated. &nbsp;This field will be a date/time stamp which identifies the &quot=
;last update&quot; of the record. &nbsp;This field will be called PGR=5FTIM=
E for lack of a better name. &nbsp;Because this field will be used from wit=
hin programs and triggers it can be longer so as to not mistake it for a us=
er field.</P><P>3) For each table to be replicated the replication system w=
ill programatically add one plpgsql function and trigger to modify the PGR=
=5FTIME field on both UPDATEs and INSERTs. &nbsp;The name of this function =
and trigger will be along the lines of &lt;table=5Fname&gt;=5Freplication=
=5Fupdate=5Ftrigger and &lt;table=5Fname&gt;=5Freplication=5Fupdate=5Ffunct=
ion. &nbsp;The function is a simple two-line chunk of code to set the field=
PGR=5FTIME equal to NOW. &nbsp;The trigger is called before each insert/up=
date. &nbsp;When looking at the Docs I see that times are stored in Zulu (G=
T) time. &nbsp;Because of this I don't have to worry about time zones and t=
he like. &nbsp;I need direction on this part (such as &quot;hey dummy, look=
at page N of file X.&quot;).</P><P>4) At this point we have tables which c=
an, at a basic level, tell the replication system when they were last updat=
ed.</P><P>5) The replication system will have a database of its own to reco=
rd the last replication event, hold configuration, logs, etc. &nbsp;I'd pre=
fer to store the configuration in a PostgreSQL table but it could just as e=
asily be stored in a text file on the filesystem somewhere.</P><P>6) To han=
dle replication I basically check the local &quot;last replication time&quo=
t; and compare it against the remote PGR=5FTIME fields. &nbsp;If the remote=
PGR=5FTIME is greater than the last replication time then change the local=
copy of the database, otherwise, change the remote end of the database. &n=
bsp;At this point I don't have a way to know WHICH field changed between th=
e two replicas so either I do ROW level replication or I check each field. =
&nbsp;I check PGR=5FTIME to determine which field is the most current. &nbs=
p;Some fine tuning of this process will have to occur no doubt.</P><P>7) Th=
e commandline utility, fired off by something like cron, could run several =
times during the day -- command line parameters can be implemented to say P=
USH ALL CHANGES TO SERVER A, or PULL ALL CHANGES FROM SERVER B.</P><P>&nbsp=
;</P><P>Questions/Concerns:</P><P>1) How far do I go with this? &nbsp;Do I =
start manhandling the system catalogs (pg=5F* tables)?</P><P>2) As to #2 an=
d #3 above, I really don't like tools automagically changing my tables but =
at this point I don't see a way around it. &nbsp;I guess this is where the =
testing comes into play.</P><P>3) Security: the replication app will have t=
o have pretty good rights to the database so it can add the nessecary funct=
ions and triggers, modify table schema, etc. &nbsp;</P><P>&nbsp;</P><P>&nbs=
p; So, any &quot;you're insane and should run home to momma&quot; comments?=
</P><P>&nbsp;</P><P>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Damond=
</P><P></P>=
************
From owner-pgsql-hackers@hub.org Fri Dec 24 18:31:03 1999
Received: from renoir.op.net (root@renoir.op.net [207.29.195.4])
by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id TAA26244
for <pgman@candle.pha.pa.us>; Fri, 24 Dec 1999 19:31:02 -0500 (EST)
Received: from hub.org (hub.org [216.126.84.1]) by renoir.op.net (o1/$Revision: 1.1 $) with ESMTP id TAA12730 for <pgman@candle.pha.pa.us>; Fri, 24 Dec 1999 19:30:05 -0500 (EST)
Received: from localhost (majordom@localhost)
by hub.org (8.9.3/8.9.3) with SMTP id TAA57851;
Fri, 24 Dec 1999 19:23:31 -0500 (EST)
(envelope-from owner-pgsql-hackers)
Received: by hub.org (bulk_mailer v1.5); Fri, 24 Dec 1999 19:22:54 -0500
Received: (from majordom@localhost)
by hub.org (8.9.3/8.9.3) id TAA57710
for pgsql-hackers-outgoing; Fri, 24 Dec 1999 19:21:56 -0500 (EST)
(envelope-from owner-pgsql-hackers@postgreSQL.org)
Received: from Mail.austin.rr.com (sm2.texas.rr.com [24.93.35.55])
by hub.org (8.9.3/8.9.3) with ESMTP id TAA57680
for <pgsql-hackers@postgresql.org>; Fri, 24 Dec 1999 19:21:25 -0500 (EST)
(envelope-from ELOEHR@austin.rr.com)
Received: from austin.rr.com ([24.93.40.248]) by Mail.austin.rr.com with Microsoft SMTPSVC(5.5.1877.197.19);
Fri, 24 Dec 1999 18:12:50 -0600
Message-ID: <38640E2D.75136600@austin.rr.com>
Date: Fri, 24 Dec 1999 18:22:05 -0600
From: Ed Loehr <ELOEHR@austin.rr.com>
X-Mailer: Mozilla 4.7 [en] (X11; U; Linux 2.2.12-20smp i686)
X-Accept-Language: en
MIME-Version: 1.0
To: DWalker@black-oak.com
CC: pgsql-hackers@postgreSQL.org
Subject: Re: [HACKERS] database replication
References: <OFD38C9424.B391F434-ON85256851.0054F41A@black-oak.COM>
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Sender: owner-pgsql-hackers@postgreSQL.org
Status: OR
DWalker@black-oak.com wrote:
> 6) To handle replication I basically check the local "last
> replication time" and compare it against the remote PGR_TIME
> fields. If the remote PGR_TIME is greater than the last replication
> time then change the local copy of the database, otherwise, change
> the remote end of the database. At this point I don't have a way to
> know WHICH field changed between the two replicas so either I do ROW
> level replication or I check each field. I check PGR_TIME to
> determine which field is the most current. Some fine tuning of this
> process will have to occur no doubt.
Interesting idea. I can see how this might sync up two databases
somehow. For true replication, however, I would always want every
replicated database to be, at the very least, internally consistent
(i.e., referential integrity), even if it was a little behind on
processing transactions. In this method, its not clear how
consistency is every achieved/guaranteed at any point in time if the
input stream of changes is continuous. If the input stream ceased,
then I can see how this approach might eventually catch up and totally
resync everything, but it looks *very* computationally expensive.
But I might have missed something. How would internal consistency be
maintained?
> 7) The commandline utility, fired off by something like cron, could
> run several times during the day -- command line parameters can be
> implemented to say PUSH ALL CHANGES TO SERVER A, or PULL ALL CHANGES
> FROM SERVER B.
My two cents is that, while I can see this kind of database syncing as
valuable, this is not the kind of "replication" I had in mind. This
may already possible by simply copying the database. What replication
means to me is a live, continuously streaming sequence of updates from
one database to another where the replicated database is always
internally consistent, available for read-only queries, and never "too
far" out of sync with the source/primary database.
What does replication mean to others?
Cheers,
Ed Loehr
************
From owner-pgsql-hackers@hub.org Fri Dec 24 21:31:10 1999
Received: from renoir.op.net (root@renoir.op.net [207.29.195.4])
by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id WAA02578
for <pgman@candle.pha.pa.us>; Fri, 24 Dec 1999 22:31:09 -0500 (EST)
Received: from hub.org (hub.org [216.126.84.1]) by renoir.op.net (o1/$Revision: 1.1 $) with ESMTP id WAA16641 for <pgman@candle.pha.pa.us>; Fri, 24 Dec 1999 22:18:56 -0500 (EST)
Received: from localhost (majordom@localhost)
by hub.org (8.9.3/8.9.3) with SMTP id WAA89135;
Fri, 24 Dec 1999 22:11:12 -0500 (EST)
(envelope-from owner-pgsql-hackers)
Received: by hub.org (bulk_mailer v1.5); Fri, 24 Dec 1999 22:10:56 -0500
Received: (from majordom@localhost)
by hub.org (8.9.3/8.9.3) id WAA89019
for pgsql-hackers-outgoing; Fri, 24 Dec 1999 22:09:59 -0500 (EST)
(envelope-from owner-pgsql-hackers@postgreSQL.org)
Received: from bocs170n.black-oak.COM ([38.149.137.131])
by hub.org (8.9.3/8.9.3) with ESMTP id WAA88957;
Fri, 24 Dec 1999 22:09:11 -0500 (EST)
(envelope-from dwalker@black-oak.com)
Received: from gcx80 ([151.196.99.113])
by bocs170n.black-oak.COM (Lotus Domino Release 5.0.1)
with SMTP id 1999122422080835:6 ;
Fri, 24 Dec 1999 22:08:08 -0500
Message-ID: <001b01bf4e9e$647287d0$af63a8c0@walkers.org>
From: "Damond Walker" <dwalker@black-oak.com>
To: <owner-pgsql-hackers@postgreSQL.org>
Cc: <pgsql-hackers@postgreSQL.org>
References: <OFD38C9424.B391F434-ON85256851.0054F41A@black-oak.COM> <38640E2D.75136600@austin.rr.com>
Subject: Re: [HACKERS] database replication
Date: Fri, 24 Dec 1999 22:07:55 -0800
MIME-Version: 1.0
X-Priority: 3 (Normal)
X-MSMail-Priority: Normal
X-Mailer: Microsoft Outlook Express 5.00.2314.1300
X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2314.1300
X-MIMETrack: Itemize by SMTP Server on notes01n/BOCS(Release 5.0.1|July 16, 1999) at 12/24/99
10:08:09 PM,
Serialize by Router on notes01n/BOCS(Release 5.0.1|July 16, 1999) at 12/24/99
10:08:11 PM,
Serialize complete at 12/24/99 10:08:11 PM
Content-Transfer-Encoding: 7bit
Content-Type: text/plain;
charset="iso-8859-1"
Sender: owner-pgsql-hackers@postgreSQL.org
Status: OR
>
> Interesting idea. I can see how this might sync up two databases
> somehow. For true replication, however, I would always want every
> replicated database to be, at the very least, internally consistent
> (i.e., referential integrity), even if it was a little behind on
> processing transactions. In this method, its not clear how
> consistency is every achieved/guaranteed at any point in time if the
> input stream of changes is continuous. If the input stream ceased,
> then I can see how this approach might eventually catch up and totally
> resync everything, but it looks *very* computationally expensive.
>
What's the typical unit of work for the database? Are we talking about
update transactions which span the entire DB? Or are we talking about
updating maybe 1% or less of the database everyday? I'd think it would be
more towards the latter than the former. So, yes, this process would be
computationally expensive but how many records would actually have to be
sent back and forth?
> But I might have missed something. How would internal consistency be
> maintained?
>
Updates that occur at site A will be moved to site B and vice versa.
Consistency would be maintained. The only problem that I can see right off
the bat would be what if site A and site B made changes to a row and then
site C was brought into the picture? Which one wins?
Someone *has* to win when it comes to this type of thing. You really
DON'T want to start merging row changes...
>
> My two cents is that, while I can see this kind of database syncing as
> valuable, this is not the kind of "replication" I had in mind. This
> may already possible by simply copying the database. What replication
> means to me is a live, continuously streaming sequence of updates from
> one database to another where the replicated database is always
> internally consistent, available for read-only queries, and never "too
> far" out of sync with the source/primary database.
>
Sounds like you're talking about distributed transactions to me. That's
an entirely different subject all-together. What you describe can be done
by copying a database...but as you say, this would only work in a read-only
situation.
Damond
************
From owner-pgsql-hackers@hub.org Sat Dec 25 16:35:07 1999
Received: from hub.org (hub.org [216.126.84.1])
by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id RAA28890
for <pgman@candle.pha.pa.us>; Sat, 25 Dec 1999 17:35:05 -0500 (EST)
Received: from localhost (majordom@localhost)
by hub.org (8.9.3/8.9.3) with SMTP id RAA86997;
Sat, 25 Dec 1999 17:29:10 -0500 (EST)
(envelope-from owner-pgsql-hackers)
Received: by hub.org (bulk_mailer v1.5); Sat, 25 Dec 1999 17:28:09 -0500
Received: (from majordom@localhost)
by hub.org (8.9.3/8.9.3) id RAA86863
for pgsql-hackers-outgoing; Sat, 25 Dec 1999 17:27:11 -0500 (EST)
(envelope-from owner-pgsql-hackers@postgreSQL.org)
Received: from mtiwmhc08.worldnet.att.net (mtiwmhc08.worldnet.att.net [204.127.131.19])
by hub.org (8.9.3/8.9.3) with ESMTP id RAA86798
for <pgsql-hackers@postgreSQL.org>; Sat, 25 Dec 1999 17:26:34 -0500 (EST)
(envelope-from pgsql@rkirkpat.net)
Received: from [192.168.3.100] ([12.74.72.219])
by mtiwmhc08.worldnet.att.net (InterMail v03.02.07.07 118-134)
with ESMTP id <19991225222554.VIOL28505@[12.74.72.219]>;
Sat, 25 Dec 1999 22:25:54 +0000
Date: Sat, 25 Dec 1999 15:25:47 -0700 (MST)
From: Ryan Kirkpatrick <pgsql@rkirkpat.net>
X-Sender: rkirkpat@excelsior.rkirkpat.net
To: DWalker@black-oak.com
cc: pgsql-hackers@postgreSQL.org
Subject: Re: [HACKERS] database replication
In-Reply-To: <OFD38C9424.B391F434-ON85256851.0054F41A@black-oak.COM>
Message-ID: <Pine.LNX.4.10.9912251433310.1551-100000@excelsior.rkirkpat.net>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Sender: owner-pgsql-hackers@postgreSQL.org
Status: OR
On Fri, 24 Dec 1999 DWalker@black-oak.com wrote:
> I've been toying with the idea of implementing database replication
> for the last few days.
I too have been thinking about this some over the last year or
two, just trying to find a quick and easy way to do it. I am not so
interested in replication, as in synchronization, as in between a desktop
machine and a laptop, so I can keep the databases on each in sync with
each other. For this sort of purpose, both the local and remote databases
would be "idle" at the time of syncing.
> 2) The replication system will need to add at least one field to each
> table in each database that needs to be replicated. This field will be
> a date/time stamp which identifies the "last update" of the record.
> This field will be called PGR_TIME for lack of a better name.
> Because this field will be used from within programs and triggers it
> can be longer so as to not mistake it for a user field.
How about a single, seperate table with the fields of 'database',
'tablename', 'oid', 'last_changed', that would store the same data as your
PGR_TIME field. It would be seperated from the actually data tables, and
therefore would be totally transparent to any database interface
applications. The 'oid' field would hold each row's OID, a nice, unique
identification number for the row, while the other fields would tell which
table and database the oid is in. Then this table can be compared with the
this table on a remote machine to quickly find updates and changes, then
each differences can be dealt with in turn.
> 3) For each table to be replicated the replication system will
> programatically add one plpgsql function and trigger to modify the
> PGR_TIME field on both UPDATEs and INSERTs. The name of this function
> and trigger will be along the lines of
> <table_name>_replication_update_trigger and
> <table_name>_replication_update_function. The function is a simple
> two-line chunk of code to set the field PGR_TIME equal to NOW. The
> trigger is called before each insert/update. When looking at the Docs
> I see that times are stored in Zulu (GT) time. Because of this I
> don't have to worry about time zones and the like. I need direction
> on this part (such as "hey dummy, look at page N of file X.").
I like this idea, better than any I have come up with yet. Though,
how are you going to handle DELETEs?
> 6) To handle replication I basically check the local "last replication
> time" and compare it against the remote PGR_TIME fields. If the
> remote PGR_TIME is greater than the last replication time then change
> the local copy of the database, otherwise, change the remote end of
> the database. At this point I don't have a way to know WHICH field
> changed between the two replicas so either I do ROW level replication
> or I check each field. I check PGR_TIME to determine which field is
> the most current. Some fine tuning of this process will have to occur
> no doubt.
Yea, this is indeed the sticky part, and would indeed require some
fine-tunning. Basically, the way I see it, is if the two timestamps for a
single row do not match (or even if the row and therefore timestamp is
missing on one side or the other altogether):
local ts > remote ts => Local row is exported to remote.
remote ts > local ts => Remote row is exported to local.
local ts > last sync time && no remote ts =>
Local row is inserted on remote.
local ts < last sync time && no remote ts =>
Local row is deleted.
remote ts > last sync time && no local ts =>
Remote row is inserted on local.
remote ts < last sync time && no local ts =>
Remote row is deleted.
where the synchronization process is running on the local machine. By
exported, I mean the local values are sent to the remote machine, and the
row on that remote machine is updated to the local values. How does this
sound?
> 7) The commandline utility, fired off by something like cron, could
> run several times during the day -- command line parameters can be
> implemented to say PUSH ALL CHANGES TO SERVER A, or PULL ALL CHANGES
> FROM SERVER B.
Or run manually for my purposes. Also, maybe follow it
with a vacuum run on both sides for all databases, as this is going to
potenitally cause lots of table changes that could stand with a cleanup.
> 1) How far do I go with this? Do I start manhandling the system catalogs (pg_* tables)?
Initially, I would just stick to user table data... If you have
changes in triggers and other meta-data/executable code, you are going to
want to make syncs of that stuff manually anyway. At least I would want
to.
> 2) As to #2 and #3 above, I really don't like tools automagically
> changing my tables but at this point I don't see a way around it. I
> guess this is where the testing comes into play.
Hence the reason for the seperate table with just a row's
identification and last update time. Only modifications to the synced
database is the update trigger, which should be pretty harmless.
> 3) Security: the replication app will have to have pretty good rights
> to the database so it can add the nessecary functions and triggers,
> modify table schema, etc.
Just run the sync program as the postgres super user, and there
are no problems. :)
> So, any "you're insane and should run home to momma" comments?
No, not at all. Though it probably should be remaned from
replication to synchronization. The former is usually associated with a
continuous stream of updates between the local and remote databases, so
they are almost always in sync, and have a queuing ability if their
connection is loss for span of time as well. Very complex and difficult to
implement, and would require hacking server code. :( Something only Sybase
and Oracle have (as far as I know), and from what I have seen of Sybase's
replication server support (dated by 5yrs) it was a pain to setup and get
running correctly.
The latter, synchronization, is much more managable, and can still
be useful, especially when you have a large database you want in two
places, mainly for read only purposes at one end or the other, but don't
want to waste the time/bandwidth to move and load the entire database each
time it changes on one end or the other. Same idea as mirroring software
for FTP sites, just transfers the changes, and nothing more.
I also like the idea of using Python. I have been using it
recently for some database interfaces (to PostgreSQL of course :), and it
is a very nice language to work with. Some worries about performance of
the program though, as python is only an interpreted lanuage, and I have
yet to really be impressed with the speed of execution of my database
interfaces yet.
Anyway, it sound like a good project, and finally one where I
actually have a clue of what is going on, and the skills to help. So, if
you are interested in pursing this project, I would be more than glad to
help. TTYL.
---------------------------------------------------------------------------
| "For to me to live is Christ, and to die is gain." |
| --- Philippians 1:21 (KJV) |
---------------------------------------------------------------------------
| Ryan Kirkpatrick | Boulder, Colorado | http://www.rkirkpat.net/ |
---------------------------------------------------------------------------
************
From owner-pgsql-hackers@hub.org Sun Dec 26 08:31:09 1999
Received: from renoir.op.net (root@renoir.op.net [207.29.195.4])
by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id JAA17976
for <pgman@candle.pha.pa.us>; Sun, 26 Dec 1999 09:31:07 -0500 (EST)
Received: from hub.org (hub.org [216.126.84.1]) by renoir.op.net (o1/$Revision: 1.1 $) with ESMTP id JAA23337 for <pgman@candle.pha.pa.us>; Sun, 26 Dec 1999 09:28:36 -0500 (EST)
Received: from localhost (majordom@localhost)
by hub.org (8.9.3/8.9.3) with SMTP id JAA90738;
Sun, 26 Dec 1999 09:21:58 -0500 (EST)
(envelope-from owner-pgsql-hackers)
Received: by hub.org (bulk_mailer v1.5); Sun, 26 Dec 1999 09:19:19 -0500
Received: (from majordom@localhost)
by hub.org (8.9.3/8.9.3) id JAA90498
for pgsql-hackers-outgoing; Sun, 26 Dec 1999 09:18:21 -0500 (EST)
(envelope-from owner-pgsql-hackers@postgreSQL.org)
Received: from bocs170n.black-oak.COM ([38.149.137.131])
by hub.org (8.9.3/8.9.3) with ESMTP id JAA90452
for <pgsql-hackers@postgreSQL.org>; Sun, 26 Dec 1999 09:17:54 -0500 (EST)
(envelope-from dwalker@black-oak.com)
Received: from vmware98 ([151.196.99.113])
by bocs170n.black-oak.COM (Lotus Domino Release 5.0.1)
with SMTP id 1999122609164808:7 ;
Sun, 26 Dec 1999 09:16:48 -0500
Message-ID: <002201bf4fb3$623f0220$b263a8c0@vmware98.walkers.org>
From: "Damond Walker" <dwalker@black-oak.com>
To: "Ryan Kirkpatrick" <pgsql@rkirkpat.net>
Cc: <pgsql-hackers@postgreSQL.org>
Subject: Re: [HACKERS] database replication
Date: Sun, 26 Dec 1999 10:10:41 -0500
MIME-Version: 1.0
X-Priority: 3 (Normal)
X-MSMail-Priority: Normal
X-Mailer: Microsoft Outlook Express 4.72.3110.1
X-MimeOLE: Produced By Microsoft MimeOLE V4.72.3110.3
X-MIMETrack: Itemize by SMTP Server on notes01n/BOCS(Release 5.0.1|July 16, 1999) at 12/26/99
09:16:51 AM,
Serialize by Router on notes01n/BOCS(Release 5.0.1|July 16, 1999) at 12/26/99
09:16:54 AM,
Serialize complete at 12/26/99 09:16:54 AM
Content-Transfer-Encoding: 7bit
Content-Type: text/plain;
charset="iso-8859-1"
Sender: owner-pgsql-hackers@postgreSQL.org
Status: OR
>
> I too have been thinking about this some over the last year or
>two, just trying to find a quick and easy way to do it. I am not so
>interested in replication, as in synchronization, as in between a desktop
>machine and a laptop, so I can keep the databases on each in sync with
>each other. For this sort of purpose, both the local and remote databases
>would be "idle" at the time of syncing.
>
I don't think it would matter if the databases are idle or not to be
honest with you. At any single point in time when you replicate I'd figure
that the database would be in a consistent state. So, you should be able to
replicate (or sync) a remote database that is in use. After all, you're
getting a snapshot of the database as it stands at 8:45 PM. At 8:46 PM it
may be totally different...but the next time syncing takes place those
changes would appear in your local copy.
The one problem you may run into is if the remote host is running a
large batch process. It's very likely that you will get 50% of their
changes when you replicate...but then again, that's why you can schedule the
event to work around such things.
> How about a single, seperate table with the fields of 'database',
>'tablename', 'oid', 'last_changed', that would store the same data as your
>PGR_TIME field. It would be seperated from the actually data tables, and
>therefore would be totally transparent to any database interface
>applications. The 'oid' field would hold each row's OID, a nice, unique
>identification number for the row, while the other fields would tell which
>table and database the oid is in. Then this table can be compared with the
>this table on a remote machine to quickly find updates and changes, then
>each differences can be dealt with in turn.
>
The problem with OID's is that they are unique at the local level but if
you try and use them between servers you can run into overlap. Also, if a
database is under heavy use this table could quickly become VERY large. Add
indexes to this table to help performance and you're taking up even more
disk space.
Using the PGR_TIME field with an index will allow us to find rows which
have changed VERY quickly. All we need to do now is somehow programatically
find the primary key for a table so the person setting up replication (or
syncing) doesn't have to have an indepth knowledge of the schema in order to
setup a syncing schedule.
>
> I like this idea, better than any I have come up with yet. Though,
>how are you going to handle DELETEs?
>
Oops...how about defining a trigger for this? With deletion I guess we
would have to move a flag into another table saying we deleted record 'X'
with this primary key from this table.
>
> Yea, this is indeed the sticky part, and would indeed require some
>fine-tunning. Basically, the way I see it, is if the two timestamps for a
>single row do not match (or even if the row and therefore timestamp is
>missing on one side or the other altogether):
> local ts > remote ts => Local row is exported to remote.
> remote ts > local ts => Remote row is exported to local.
> local ts > last sync time && no remote ts =>
> Local row is inserted on remote.
> local ts < last sync time && no remote ts =>
> Local row is deleted.
> remote ts > last sync time && no local ts =>
> Remote row is inserted on local.
> remote ts < last sync time && no local ts =>
> Remote row is deleted.
>where the synchronization process is running on the local machine. By
>exported, I mean the local values are sent to the remote machine, and the
>row on that remote machine is updated to the local values. How does this
>sound?
>
The replication part will be the most complex...that much is for
certain...
I've been writing systems in Lotus Notes/Domino for the last year or so
and I've grown quite spoiled with what it can do in regards to replication.
It's not real-time but you have to gear your applications to this type of
thing (it's possible to create documents, fire off email to notify people of
changes and have the email arrive before the replicated documents do).
Replicating large Notes/Domino databases takes quite a while....I don't see
any kind of replication or syncing running in a blink of an eye.
Having said that, a good algo will have to be written to cut down on
network traffic and to keep database conversations down to a minimum. This
will be appreciated by people with low bandwidth connections I'm sure
(dial-ups, fractional T1's, etc).
> Or run manually for my purposes. Also, maybe follow it
>with a vacuum run on both sides for all databases, as this is going to
>potenitally cause lots of table changes that could stand with a cleanup.
>
What would a vacuum do to a system being used by many people?
> No, not at all. Though it probably should be remaned from
>replication to synchronization. The former is usually associated with a
>continuous stream of updates between the local and remote databases, so
>they are almost always in sync, and have a queuing ability if their
>connection is loss for span of time as well. Very complex and difficult to
>implement, and would require hacking server code. :( Something only Sybase
>and Oracle have (as far as I know), and from what I have seen of Sybase's
>replication server support (dated by 5yrs) it was a pain to setup and get
>running correctly.
It could probably be named either way...but the one thing I really don't
want to do is start hacking server code. The PostgreSQL people have enough
to do without worrying about trying to meld anything I've done to their
server. :)
Besides, I like the idea of having it operate as a stand-alone product.
The only PostgreSQL feature we would require would be triggers and
plpgsql...what was the earliest version of PostgreSQL that supported
plpgsql? Even then I don't see the triggers being that complex to boot.
> I also like the idea of using Python. I have been using it
>recently for some database interfaces (to PostgreSQL of course :), and it
>is a very nice language to work with. Some worries about performance of
>the program though, as python is only an interpreted lanuage, and I have
>yet to really be impressed with the speed of execution of my database
>interfaces yet.
The only thing we'd need for Python is the Python extensions for
PostgreSQL...which in turn requires libpq and that's about it. So, it
should be able to run on any platform supported by Python and libpq. Using
TK for the interface components will require NT people to get additional
software from the 'net. At least it did with older version of Windows
Python. Unix folks should be happy....assuming they have X running on the
machine doing the replication or syncing. Even then I wrote a curses based
Python interface awhile back which allows buttons, progress bars, input
fields, etc (I called it tinter and it's available at
http://iximd.com/~dwalker). It's a simple interface and could probably be
cleaned up a bit but it works. :)
> Anyway, it sound like a good project, and finally one where I
>actually have a clue of what is going on, and the skills to help. So, if
>you are interested in pursing this project, I would be more than glad to
>help. TTYL.
>
That would be a Good Thing. Have webspace somewhere? If I can get
permission from the "powers that be" at the office I could host a website on
our (Domino) webserver.
Damond
************
From owner-pgsql-hackers@hub.org Sun Dec 26 19:11:48 1999
Received: from hub.org (hub.org [216.126.84.1])
by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id UAA26661
for <pgman@candle.pha.pa.us>; Sun, 26 Dec 1999 20:11:46 -0500 (EST)
Received: from localhost (majordom@localhost)
by hub.org (8.9.3/8.9.3) with SMTP id UAA14959;
Sun, 26 Dec 1999 20:08:15 -0500 (EST)
(envelope-from owner-pgsql-hackers)
Received: by hub.org (bulk_mailer v1.5); Sun, 26 Dec 1999 20:07:27 -0500
Received: (from majordom@localhost)
by hub.org (8.9.3/8.9.3) id UAA14820
for pgsql-hackers-outgoing; Sun, 26 Dec 1999 20:06:28 -0500 (EST)
(envelope-from owner-pgsql-hackers@postgreSQL.org)
Received: from mtiwmhc02.worldnet.att.net (mtiwmhc02.worldnet.att.net [204.127.131.37])
by hub.org (8.9.3/8.9.3) with ESMTP id UAA14749
for <pgsql-hackers@postgreSQL.org>; Sun, 26 Dec 1999 20:05:39 -0500 (EST)
(envelope-from rkirkpat@rkirkpat.net)
Received: from [192.168.3.100] ([12.74.72.56])
by mtiwmhc02.worldnet.att.net (InterMail v03.02.07.07 118-134)
with ESMTP id <19991227010506.WJVW1914@[12.74.72.56]>;
Mon, 27 Dec 1999 01:05:06 +0000
Date: Sun, 26 Dec 1999 18:05:02 -0700 (MST)
From: Ryan Kirkpatrick <pgsql@rkirkpat.net>
X-Sender: rkirkpat@excelsior.rkirkpat.net
To: Damond Walker <dwalker@black-oak.com>
cc: pgsql-hackers@postgreSQL.org
Subject: Re: [HACKERS] database replication
In-Reply-To: <002201bf4fb3$623f0220$b263a8c0@vmware98.walkers.org>
Message-ID: <Pine.LNX.4.10.9912261742550.7666-100000@excelsior.rkirkpat.net>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Sender: owner-pgsql-hackers@postgreSQL.org
Status: OR
On Sun, 26 Dec 1999, Damond Walker wrote:
> > How about a single, seperate table with the fields of 'database',
> >'tablename', 'oid', 'last_changed', that would store the same data as your
> >PGR_TIME field. It would be seperated from the actually data tables, and
...
> The problem with OID's is that they are unique at the local level but if
> you try and use them between servers you can run into overlap.
Yea, forgot about that point, but became dead obvious once you
mentioned it. Boy, I feel stupid now. :)
> Using the PGR_TIME field with an index will allow us to find rows which
> have changed VERY quickly. All we need to do now is somehow programatically
> find the primary key for a table so the person setting up replication (or
> syncing) doesn't have to have an indepth knowledge of the schema in order to
> setup a syncing schedule.
Hmm... Yea, maybe look to see which field(s) has a primary, unique
index on it? Then use those field(s) as a primary key. Just require that
any table to be synchronized to have some set of fields that uniquely
identify each row. Either that, or add another field to each table with
our own, cross system consistent, identification system. Don't know which
would be more efficient and easier to work with.
The former could potentially get sticky if it takes a lots of
fields to generate a unique key value, but has the smallest effect on the
table to be synced. The latter could be difficult to keep straight between
systems (local vs. remote), and would require a trigger on inserts to
generate a new, unique id number, that does not exist locally or
remotely (nasty issue there), but would remove the uniqueness
requirement.
> Oops...how about defining a trigger for this? With deletion I guess we
> would have to move a flag into another table saying we deleted record 'X'
> with this primary key from this table.
Or, according to my logic below, if a row is missing on one side
or the other, then just compare the remaining row's timestamp to the last
synchronization time (stored in a seperate table/db elsewhere). The
results of the comparsion and the state of row existences tell one if the
row was inserted or deleted since the last sync, and what should be done
to perform the sync.
> > Yea, this is indeed the sticky part, and would indeed require some
> >fine-tunning. Basically, the way I see it, is if the two timestamps for a
> >single row do not match (or even if the row and therefore timestamp is
> >missing on one side or the other altogether):
> > local ts > remote ts => Local row is exported to remote.
> > remote ts > local ts => Remote row is exported to local.
> > local ts > last sync time && no remote ts =>
> > Local row is inserted on remote.
> > local ts < last sync time && no remote ts =>
> > Local row is deleted.
> > remote ts > last sync time && no local ts =>
> > Remote row is inserted on local.
> > remote ts < last sync time && no local ts =>
> > Remote row is deleted.
> >where the synchronization process is running on the local machine. By
> >exported, I mean the local values are sent to the remote machine, and the
> >row on that remote machine is updated to the local values. How does this
> >sound?
> Having said that, a good algo will have to be written to cut down on
> network traffic and to keep database conversations down to a minimum. This
> will be appreciated by people with low bandwidth connections I'm sure
> (dial-ups, fractional T1's, etc).
Of course! In reflection, the assigned identification number I
mentioned above might be the best then, instead of having to transfer the
entire set of key fields back and forth.
> What would a vacuum do to a system being used by many people?
Probably lock them out of tables while they are vacuumed... Maybe
not really required in the end, possibly optional?
> It could probably be named either way...but the one thing I really don't
> want to do is start hacking server code. The PostgreSQL people have enough
> to do without worrying about trying to meld anything I've done to their
> server. :)
Yea, they probably would appreciate that. They already have enough
on thier plate for 7.x as it is! :)
> Besides, I like the idea of having it operate as a stand-alone product.
> The only PostgreSQL feature we would require would be triggers and
> plpgsql...what was the earliest version of PostgreSQL that supported
> plpgsql? Even then I don't see the triggers being that complex to boot.
No, provided that we don't do the identification number idea
(which the more I think about it, probably will not work). As for what
version support plpgsql, I don't know, one of the more hard-core pgsql
hackers can probably tell us that.
> The only thing we'd need for Python is the Python extensions for
> PostgreSQL...which in turn requires libpq and that's about it. So, it
> should be able to run on any platform supported by Python and libpq.
Of course. If it ran on NT as well as Linux/Unix, that would be
even better. :)
> Unix folks should be happy....assuming they have X running on the
> machine doing the replication or syncing. Even then I wrote a curses
> based Python interface awhile back which allows buttons, progress
> bars, input fields, etc (I called it tinter and it's available at
> http://iximd.com/~dwalker). It's a simple interface and could
> probably be cleaned up a bit but it works. :)
Why would we want any type of GUI (X11 or curses) for this sync
program. I imagine just a command line program with a few options (local
machine, remote machine, db name, etc...), and nothing else.
Though I will take a look at your curses interface, as I have been
wanting to make a curses interface to a few db interfaces I have, in a
simple as manner as possible.
> That would be a Good Thing. Have webspace somewhere? If I can get
> permission from the "powers that be" at the office I could host a website on
> our (Domino) webserver.
Yea, I got my own web server (www.rkirkpat.net) with 1GB+ of disk
space available, sitting on a decent speed DSL. Even can setup of a
virtual server if we want (i.e. pgsync.rkirkpat.net :). CVS repository,
email lists, etc... possible with some effort (and time).
So, where should we start? TTYL.
PS. The current pages on my web site are very out of date at the
moment (save for the pgsql information). I hope to have updated ones up
within the week.
---------------------------------------------------------------------------
| "For to me to live is Christ, and to die is gain." |
| --- Philippians 1:21 (KJV) |
---------------------------------------------------------------------------
| Ryan Kirkpatrick | Boulder, Colorado | http://www.rkirkpat.net/ |
---------------------------------------------------------------------------
************
From owner-pgsql-hackers@hub.org Mon Dec 27 12:33:32 1999
Received: from hub.org (hub.org [216.126.84.1])
by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id NAA24817
for <pgman@candle.pha.pa.us>; Mon, 27 Dec 1999 13:33:29 -0500 (EST)
Received: from localhost (majordom@localhost)
by hub.org (8.9.3/8.9.3) with SMTP id NAA53391;
Mon, 27 Dec 1999 13:29:02 -0500 (EST)
(envelope-from owner-pgsql-hackers)
Received: by hub.org (bulk_mailer v1.5); Mon, 27 Dec 1999 13:28:38 -0500
Received: (from majordom@localhost)
by hub.org (8.9.3/8.9.3) id NAA53248
for pgsql-hackers-outgoing; Mon, 27 Dec 1999 13:27:40 -0500 (EST)
(envelope-from owner-pgsql-hackers@postgreSQL.org)
Received: from gtv.ca (h139-142-238-17.cg.fiberone.net [139.142.238.17])
by hub.org (8.9.3/8.9.3) with ESMTP id NAA53170
for <pgsql-hackers@hub.org>; Mon, 27 Dec 1999 13:26:40 -0500 (EST)
(envelope-from aaron@genisys.ca)
Received: from stilborne (24.67.90.252.ab.wave.home.com [24.67.90.252])
by gtv.ca (8.9.3/8.8.7) with SMTP id MAA01200
for <pgsql-hackers@hub.org>; Mon, 27 Dec 1999 12:36:39 -0700
From: "Aaron J. Seigo" <aaron@gtv.ca>
To: pgsql-hackers@hub.org
Subject: Re: [HACKERS] database replication
Date: Mon, 27 Dec 1999 11:23:19 -0700
X-Mailer: KMail [version 1.0.28]
Content-Type: text/plain
References: <199912271135.TAA10184@netrinsics.com>
In-Reply-To: <199912271135.TAA10184@netrinsics.com>
MIME-Version: 1.0
Message-Id: <99122711245600.07929@stilborne>
Content-Transfer-Encoding: 8bit
Sender: owner-pgsql-hackers@postgreSQL.org
Status: OR
hi..
> Before anyone starts implementing any database replication, I'd strongly
> suggest doing some research, first:
>
> http://sybooks.sybase.com:80/onlinebooks/group-rs/rsg1150e/rs_admin/@Generic__BookView;cs=default;ts=default
good idea, but perhaps sybase isn't the best study case.. here's some extremely
detailed online coverage of Oracle 8i's replication, from the oracle online
library:
http://bach.towson.edu/oracledocs/DOC/server803/A54651_01/toc.htm
--
Aaron J. Seigo
Sys Admin
************

7
doc/src/FAQ.html
View File

@ -628,7 +628,7 @@ support configured in your kernel at all.<P>
accessing my PostgreSQL database?</H4><P>
By default, PostgreSQL only allows connections from the local machine
using unix domain sockets. Other machines will not be able to connect
using Unix domain sockets. Other machines will not be able to connect
unless you add the <I>-i</I> flag to the <I>postmaster,</I>
<B>and</B> enable host-based authentication by modifying the file
<I>$PGDATA/pg_hba.conf</I> accordingly. This will allow TCP/IP connections.
@ -852,9 +852,12 @@ Maximum size for a table? unlimited on all operating systems
Maximum size for a row? 8k, configurable to 32k
Maximum number of rows in a table? unlimited
Maximum number of columns table? unlimited
Maximun number of indexes on a table? unlimited
Maximum number of indexes on a table? unlimited
</PRE>
Of course, these are not actually unlimited, but limited to available
disk space.<P>
To change the maximum row size, edit <I>include/config.h</I> and change
<SMALL>BLCKSZ.</SMALL> To use attributes larger than 8K, you can also
use the large object interface.<P>