Hi Ahmad, There is no one-liner answer to these questions, as the code produced depends on many decisions taken in the SQL-> MAL compiler/optimizer. Most of them reporeted by you have to do with the MVCC code management and the rest are individual kernel MAL instructions. A look at the underlying implementation will show that access patterns depend on many properties of the objects being accessed. All optimized for the situation at hand. Success with your study of the MonetDB code base. regards, Martin On 4/29/13 8:43 PM, Hassan, Ahmad wrote:
Hi All,
I am analysing the monetdb memory access pattern to identify various strides in LLC accesses. But most of the accesses per object are being observed as non-strided which is not what I expected. As monetdb involves BATs and these are arrays so I was thinking that there would be more strided pattern rather than random accesses unless BAT arrays are being treated as trees and random access is being used to access the items. To understand it further, I have now retrieved the execution plan of TPCH Q1 and the plan has various segments like follows:
X_455:bat[:oid,:str] := sql.bind(X_7,"sys","lineitem","l_linestatus",2,5,16);
X_1346 := algebra.kdifference(X_400,X_455);
X_1379 := algebra.kunion(X_1346,X_455);
X_1412 := algebra.leftjoin(X_1180,X_1379);
(X_1452,X_1453) := group.multicolumns(X_1293,X_1412);
X_1514 := bat.mirror(X_1452);
X_1516 := algebra.leftjoin(X_1514,X_1412);
I have two questions:
1)As there are many repeated segments like above in whole query plan, so what is the context behind multiple repeated segments please.
2)I want to understand what is the input to most common operators like leftjoin, kdifference, kunion and whether they process those inputs sequentially or randomly. What is the best way to get this understanding please? From the plan it is obvious that the input is the BAT(s), but how do the operators access the BAT is really a question.
Thanks for the help.
Kind Regards, Ahmad
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