Cost-Based Optimization of Integration Flows - Datenbanken ...

3.4 Optimization Techniques
Assign (o1)
[out: msg1]
Invoke (o2)
[service s6, in: msg1]
4ms
21ms
subsequence 1
Assign (o3)
[out: msg2]
3ms
Assign (o1)
[out: msg1]
4ms
Assign (o4)
[out: msg3]
4ms
Invoke (o2)
[service s6, in: msg1]
21ms
Invoke (o5)
[service s6, in: msg2, out: msg4]
Invoke (o6)
[service s6, in: msg3, out: msg5]
74ms
131ms
subsequence 2
3ms
Assign (o3)
[out: msg2]
Fork (o-1)
max(81ms+3ms, 140ms+6ms)
Assign (o4)
[out: msg3]
4ms
Assign (o7)
[in: msg4, out: msg6]
4ms
74ms
Invoke (o5)
[service s6, in: msg2, out: msg4]
Invoke (o6)
[service s6, in: msg3, out: msg5]
131ms
Assign (o8)
[in: msg5, out: msg7]
5ms
4ms
Assign (o7)
[in: msg4, out: msg6]
Assign (o8)
[in: msg5, out: msg7]
5ms
Invoke (o9)
[service s7, in: msg6]
Invoke (o10)
[service s7, in: msg7]
98ms
156ms
subsequence 3
Invoke (o9)
[service s7, in: msg6]
Invoke (o10)
[service s7, in: msg7]
98ms
156ms
(a) Plan P 8
(b) Optimized Plan P ′ 8
Figure 3.13: Example Rewriting Sequences to Parallel Flows
Figure 3.13(a). The costs are estimated as Ŵ (P 8) = 500 ms. Figure 3.13(b) illustrates
the optimized plan P 8 ′ . During rewriting, the operator sequence was split by the writing
interactions o 2 (after o 2 because it is the first interaction) and o 9 (before o 9 in order to
avoid executing it in parallel to o 6 ) into three subsequences due to Rule 3 of Definition 3.1
(no parallel interactions with the same external system if one is a writing interaction).
Furthermore, for the second subsequence, we created a Fork operator with two subflows. If
we assume k = 2 logical processors and a thread start time of W (Start Thread) = 3 ms, we
estimate the costs of the Fork operator as follows: W (o −1 ) = max((81 ms+3 ms), (140 ms+
2 · 3 ms)) = 146 ms As a result, we reduced the estimated plan costs to Ŵ (P 8 ′ ) = 425 ms,
while ensuring semantic correctness at the same time. There, the Invoke operators o 5 and
o 6 can be executed in parallel because they are both reading interactions.
This optimization technique offers high optimization opportunities. With regard to
maximal optimization opportunities, this technique should be applied before the techniques
WC1 (rescheduling parallel flows) and WC4 (merging parallel flows). In order to
prevent the special case of local suboptima, we directly evaluate the techniques WC1 and
WC4 for the resulting plan (e.g., P 8 ′ from Example 3.10) if the parallel execution exhibits
higher estimated costs than the serial execution.
Rewriting Iterations to Parallel Flows
Similar to rewriting sequences, the technique WC3: Rewriting Iterations to Parallel Flows
rewrites an Iteration with r loops to a Fork operator with r concurrent subflows. This
is applicable if there are no dependencies between operators of different iteration loops.
However, foreach semantics without such dependencies are typical for integration flows.
The core idea is to use, similar to loop unrolling of programming language compilers
for parallel environments, the estimated number of iterations in order to determine the
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