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<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Arial">Hi
Michael,</SPAN><?xml:namespace prefix = o ns =
"urn:schemas-microsoft-com:office:office" /><o:p></o:p></P>
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color=#000000><FONT
face="Times New Roman"> <o:p></o:p></FONT></FONT></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Arial">I don't see any
problems for you to make changes to mondrian. But I have some
concerns:</SPAN><o:p></o:p></P>
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color=#000000><FONT
face="Times New Roman"> <o:p></o:p></FONT></FONT></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Arial">I think the changes you
are about to make are quite huge and will have an impact of how mondrian will
behave. Since this is the first source contribution you are about to make,
I urge you not to check anything into perforce before it is actually working and
passing all regression tests.</SPAN><o:p></o:p></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><FONT
color=#000000><FONT
face="Times New Roman"> <o:p></o:p></FONT></FONT></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Arial">I think most developers
of mondrian have ongoing projects that are using mondrian, I think this
is</SPAN><o:p></o:p></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Arial">becoming more and more
an important issue.</SPAN><o:p></o:p></P>
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color=#000000><FONT
face="Times New Roman"> <o:p></o:p></FONT></FONT></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Arial">For me: it must be able
to flush aggregates and member cache using the plug-in and cubes not</SPAN><FONT
face="Times New Roman" color=#000000 size=3> </FONT><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Arial">maintaining cache
should be able to load their own data, without messing with global
cache.</SPAN><o:p></o:p></P>
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color=#000000><FONT
face="Times New Roman"> <o:p></o:p></FONT></FONT></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Arial">And since a dynamic
database cannot easily be simulated in a regression test, I think if you
are</SPAN><FONT face="Times New Roman" color=#000000 size=3> </FONT><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Arial">serious about tackling
the read-consistency for near-real-time data, you need a realistic (dynamic)
database to test against. And the database must be large enough to be able
to see realistic performance.<SPAN style="mso-spacerun: yes"> </SPAN>It is
also advised to test with virtual cubes, cubes maintaining cache (with aggregate
tables) in combination with cubes not maintaining cache (without aggregate
tables), shared dimensions and so on…</SPAN><o:p></o:p></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><FONT
color=#000000><FONT
face="Times New Roman"> <o:p></o:p></FONT></FONT></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Arial">I released my project 4
weeks ago, not even using the latest version of perforce, since at a given point
mondrian-head was completely broken for me. While I know software always
has some bugs that need to be patched, things that are not tested and are
breaking mondrian should not be checked in. All too often I had to sync
with perforce to solve a bug and this ended up in a nightmare, spending most of
my time finding out what change was causing mondrian to
break.</SPAN><o:p></o:p></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><FONT
color=#000000><FONT
face="Times New Roman"> <o:p></o:p></FONT></FONT></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Arial">When mondrian 2.3 will
be released, it is most likely that there will be some 2.3.x version
containing some patches. I think it must be possible to make those patches
without having to drag new huge features along.</SPAN><o:p></o:p></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><FONT size=3><FONT
color=#000000><FONT
face="Times New Roman"> <o:p></o:p></FONT></FONT></FONT></P>
<P class=MsoNormal style="MARGIN: 0cm 0cm 0pt"><SPAN
style="FONT-SIZE: 10pt; COLOR: blue; FONT-FAMILY: Arial">Bart</SPAN><o:p></o:p></P></FONT></SPAN></DIV>
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<DIV dir=ltr align=left><FONT face=Tahoma size=2><B>From:</B>
mondrian-bounces@pentaho.org [mailto:mondrian-bounces@pentaho.org] <B>On Behalf
Of </B>michael bienstein<BR><B>Sent:</B> vrijdag 9 maart 2007
11:36<BR><B>To:</B> Mondrian developer mailing list<BR><B>Subject:</B>
[Mondrian] Multithreading etc<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV
style="FONT-SIZE: 12pt; FONT-FAMILY: times new roman, new york, times, serif">
<DIV>I sent this to the list but it gets bounced because I attached the code in
a zip file. How do I send code through without checking it in because it
is still orthogonal to the codebase?<BR><BR>Michael<BR>----<BR><BR>Well, I have
code that works for multi-threading infrastructure so I would like to know if it
is worth continuing with this or not.<BR><BR>As for ROLLUP/CUBE my thoughts
are:<BR>1) Either we keep the codebase simple by sticking to a standard
(SQL2003) even if this standard is not yet implemented widely and certain
databases have better special features than others, or we allow a per-database
SQL generation system. The argument for the second makes sense only if the
developer resources to write and maintain each dialect comes from the database
vendor or their community. Mondrian is probably at a stage that such
discussions can be undertaken with the database vendors.<BR>2) Architecturally
this implies loading multiple Aggregations from one SQL query. That
requires a rethink of the way the cell cache loading is done because at the
moment an Aggregation is loaded one at a time and in a synchronized block on the
Aggregation. Similar concerns have to be dealt with for in-memory
rollups. I think that synchronized is too forceful. We need
something more like a Lock from java.util.concurrent so we can do
tryLock(). Look at the TxLock idea I have in the code I'm
attaching.<BR><BR>As for multi-threading:<BR>I have only written most of the
base infrastructure, not the cell loading. To integrate would require a
significant amount of work in Mondrian's code to pass all interaction with
Mondrian through TxSystem.runWithTx(). <BR><BR>Basic concerns are:<BR>
<DIV class=MsoNormal
style="MARGIN-LEFT: 36pt; TEXT-INDENT: -18pt"><SPAN><SPAN>1)<SPAN
style="FONT-WEIGHT: normal; FONT-SIZE: 7pt; LINE-HEIGHT: normal; FONT-STYLE: normal; FONT-VARIANT: normal; font-size-adjust: none; font-stretch: normal">
</SPAN></SPAN></SPAN><SPAN>Threads should be able to share data related to the
request across the threads.</SPAN></DIV>
<DIV class=MsoNormal
style="MARGIN-LEFT: 36pt; TEXT-INDENT: -18pt"><SPAN><SPAN>2)<SPAN
style="FONT-WEIGHT: normal; FONT-SIZE: 7pt; LINE-HEIGHT: normal; FONT-STYLE: normal; FONT-VARIANT: normal; font-size-adjust: none; font-stretch: normal">
</SPAN></SPAN></SPAN><SPAN>A Thread should be loaned to a request and returned
in a way that is well-nigh fail-safe (i.e. the thread shouldn’t keep running of
the request fails in some way).</SPAN></DIV>
<DIV class=MsoNormal
style="MARGIN-LEFT: 36pt; TEXT-INDENT: -18pt"><SPAN><SPAN>3)<SPAN
style="FONT-WEIGHT: normal; FONT-SIZE: 7pt; LINE-HEIGHT: normal; FONT-STYLE: normal; FONT-VARIANT: normal; font-size-adjust: none; font-stretch: normal">
</SPAN></SPAN></SPAN><SPAN>We should be able in a parameter of some sort decide
to NOT use threads at all.</SPAN></DIV>
<DIV class=MsoNormal
style="MARGIN-LEFT: 36pt; TEXT-INDENT: -18pt"><SPAN><SPAN>4)<SPAN
style="FONT-WEIGHT: normal; FONT-SIZE: 7pt; LINE-HEIGHT: normal; FONT-STYLE: normal; FONT-VARIANT: normal; font-size-adjust: none; font-stretch: normal">
</SPAN></SPAN></SPAN><SPAN>The number of threads should be
configurable.</SPAN></DIV>
<DIV class=MsoNormal
style="MARGIN-LEFT: 36pt; TEXT-INDENT: -18pt"><SPAN><SPAN>5)<SPAN
style="FONT-WEIGHT: normal; FONT-SIZE: 7pt; LINE-HEIGHT: normal; FONT-STYLE: normal; FONT-VARIANT: normal; font-size-adjust: none; font-stretch: normal">
</SPAN></SPAN></SPAN><SPAN>There should be an independence from the rest of the
code base.</SPAN></DIV>
<DIV class=MsoNormal
style="MARGIN-LEFT: 36pt; TEXT-INDENT: -18pt"><SPAN><SPAN>6)<SPAN
style="FONT-WEIGHT: normal; FONT-SIZE: 7pt; LINE-HEIGHT: normal; FONT-STYLE: normal; FONT-VARIANT: normal; font-size-adjust: none; font-stretch: normal">
</SPAN></SPAN></SPAN><SPAN>We should be able to make use of custom thread pools
or use managed thread pools from the application server.</SPAN></DIV>
<DIV class=MsoNormal
style="MARGIN-LEFT: 36pt; TEXT-INDENT: -18pt"><SPAN><SPAN>7)<SPAN
style="FONT-WEIGHT: normal; FONT-SIZE: 7pt; LINE-HEIGHT: normal; FONT-STYLE: normal; FONT-VARIANT: normal; font-size-adjust: none; font-stretch: normal">
</SPAN></SPAN></SPAN><SPAN>Then there is a relatively minor issue with
read-consistency for near-real-time data that turns out to be a real
head-ache.<SPAN> </SPAN>This can be done by either: using the transaction
semantics of the underlying data store <U>or</U> modifying all SQL requests and
cache interactions with a timestamp and/or transaction id of some
sort.<SPAN> </SPAN>E.g. when an MDX requests begins it asks the underlying
data store for the id of the last completed transaction that modified data and
keeps this in a request-scope available to all threads.<SPAN> </SPAN>Then
it appends “changedTxId <= ${lastTxIdWhenFirstEntered}” to each WHERE
clause.<SPAN> </SPAN>If however we use the underlying data store’s
transactions then we must keep open the JDBC Connection for the duration of the
request reusing it on the same thread for each interaction with that data
store.</SPAN></DIV>
<DIV class=MsoNormal><SPAN>Now, I think that the best way to take advantage of
multiple threads in the storage system is NOT launching multiple SQLs on the
same star schema but different aggregations but rather to use
<U>partitioning</U> of data.<SPAN> </SPAN>That is to segment the cell data
(and maybe dimension data) based on values of certain columns.<SPAN>
</SPAN>For example year<2007 and year=2007 in<SPAN> </SPAN>two
different partitions.<SPAN> </SPAN>This can be introduced slowly by simply
making a RolapStar one Partition for the moment.<SPAN> </SPAN>Having said
that aggregation tables are also a type of Partition and hitting two of them at
once should be quite easy.</SPAN></DIV>So the design I am introducing has the
following features:<BR>1) A scope for "request" or "interaction" that is larger
than the Thread that begins it. Since this is similar to a transaction
I've called it a Tx. See the mondrian.tx package. Each sub-system in
Mondrian can enlist a representation of itself in the Tx.<BR>2) Break up the
different tasks performed into Task objects that can be run potentially in
parallel. Allow a set of Tasks to be tied to the same Thread so that the
same JDBC Connection can be used for all of them for read-consistency and
cleaned up at the end of the Tx. This is done declaratively so the
implementation can be changed easily. The implementation can also ensure
that the J2EE context is passed onto separate threads (JNDI, context class
loader etc).<BR>3) A system of fail-quick locks at the Tx scope rather than just
Thread scope. <BR><BR>If this is worth persuing as a design for the next
version then good. If not I'll stop now.<BR><BR>Michael</DIV></DIV><BR>
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