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LinDP++: Generalizing Linearized DP to Crossproducts and Non-Inner - - PowerPoint PPT Presentation
LinDP++: Generalizing Linearized DP to Crossproducts and Non-Inner - - PowerPoint PPT Presentation
LinDP++: Generalizing Linearized DP to Crossproducts and Non-Inner Joins Bernhard Radke, Thomas Neumann Technische Universitt Mnchen Join Ordering D D F E C B A Query Graph C SELECT ... F E B A AND C.d=D.d AND E.e=F.e WHERE
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Problem Complexities
◮ Join Ordering is NP-Hard
R4 R5 R6 R7 R0 R1 R2 R3 R8 R9
R1 R16 R17 R14 R15 R12 R13 R10 R11 R18 R19 R38 R39 R34 R35 R36 R37 R30 R31 R32 R33 R4 R5 R6 R7 R0 R43 R2 R3 R28 R8 R9 R49 R48 R45 R44 R47 R46 R41 R40 R29 R42 R27 R26 R25 R24 R23 R22 R21 R20
R499 R498 R491 R490 R493 R492 R495 R494 R497 R496 R396 R397 R394 R395 R392 R393 R390 R258 R257 R256 R255 R254 R253 R252 R398 R250 R262 R172 R173 R170 R171 R176 R177 R174 R175 R178 R179 R259 R391 R98 R99 R96 R97 R94 R95 R92 R93 R90 R91 R477 R476 R475 R474 R473 R472 R471 R470 R479 R478 R251 R399 R388 R213 R212 R211 R210 R217 R216 R215 R214 R219 R218 R358 R359 R352 R353 R350 R351 R356 R357 R354 R355 R70 R338 R72 R73 R74 R75 R76 R339 R78 R79 R136 R137 R134 R135 R132 R133 R130 R131 R138 R139 R238 R183 R182 R181 R180 R187 R186 R185 R184 R189 R188 R439 R438 R433 R432 R431 R430 R437 R436 R435 R434 R330 R318 R319 R316 R317 R314 R315 R312 R313 R310 R311 R38 R39 R34 R35 R36 R37 R30 R31 R32 R33 R4 R5 R6 R7 R0 R1 R2 R3 R8 R9 R381 R380 R383 R382 R385 R384 R387 R386 R389 R263 R260 R261 R266 R267 R264 R265 R169 R168 R165 R164 R167 R166 R161 R160 R163 R162 R442 R443 R440 R441 R446 R447 R444 R445 R448 R449 R361 R345 R344 R347 R346 R341 R340 R343 R342 R226 R227 R224 R225 R349 R223 R220 R221 R45 R44 R47 R46 R41 R40 R43 R42 R49 R48 R121 R120 R123 R122 R125 R124 R127 R126 R129 R128 R228 R229 R222 R348 R154 R155 R156 R157 R150 R151 R400 R153 R158 R159 R408 R409 R309 R308 R301 R300 R303 R302 R305 R304 R307 R306 R147 R146 R413 R412 R415 R414 R275 R274 R277 R276 R271 R270 R273 R272 R416 R279 R278 R378 R379 R374 R375 R376 R377 R370 R371 R372 R373 R417 R118 R119 R110 R111 R112 R113 R114 R115 R116 R117 R288 R289 R280 R281 R282 R283 R284 R285 R286 R287 R459 R458 R455 R454 R457 R456 R451 R450 R453 R452 R239 R331 R332 R333 R334 R335 R336 R337 R231 R230 R233 R232 R235 R234 R237 R236 R58 R59 R52 R53 R50 R51 R56 R57 R54 R55 R488 R489 R486 R487 R484 R485 R482 R483 R480 R481 R248 R249 R244 R245 R246 R247 R240 R241 R242 R243 R268 R269 R411 R410 R145 R144 R143 R142 R141 R140 R419 R418 R149 R148 R89 R88 R81 R80 R83 R82 R85 R84 R87 R86 R464 R465 R466 R467 R460 R461 R462 R463 R468 R469 R16 R17 R14 R15 R12 R13 R10 R11 R18 R19 R200 R201 R202 R203 R204 R205 R206 R207 R208 R209 R369 R368 R367 R366 R365 R364 R363 R362 R405 R360 R406 R407 R404 R63 R62 R61 R60 R67 R66 R65 R64 R402 R69 R68 R403 R152 R401 R109 R108 R103 R102 R101 R100 R107 R106 R105 R104 R299 R298 R71 R293 R292 R291 R290 R297 R296 R295 R294 R190 R191 R192 R193 R194 R195 R196 R197 R198 R199 R77 R428 R429 R420 R421 R422 R423 R424 R425 R426 R427 R323 R322 R321 R320 R327 R326 R325 R324 R329 R328 R29 R28 R27 R26 R25 R24 R23 R22 R21 R20Easy! Manageable Impossible? ◮ Tableau (DBTEST 2018): Queries regularly involve a few dozen joins ◮ SAP (BTW 2017): Largest query touches 4,598 relations
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Adaptive Optimization of Very Large Join Queries (SIGMOD 2018)
Query easy? 10K DP entries? corner case? medium? medium? search space linearization search space linearization solve optimally gracefully introduce greediness to keep
- ptimization time
reasonable cannot linearize GOO/DPhyp yes no yes yes no no DPhyp LinDP++ GOO/linDP
◮ For performance and correctness reasons: Do not consider crossproducts
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Search Space Linearization
◮ If the order of relations in the optimal plan is known ◮ Generating the optimal plan from this linearization takes polynomial time ◮ Optimally combine optimal solutions for subchains A B E F C D A B C E F D
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Search Space Linearization
◮ Of course: Optimal order unknown ◮ But IKKBZ (TODS 3/1984, VLDB 1986): optimal left-deep plan in O(n2) ◮ Using IKKBZ to linearize the search space yields good bushy plans
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IKKBZ
◮ Requires acyclic query graph (build MST if cyclic) ◮ Idea: Transform precedence graphs into a linear order ◮ Assign ranks to nodes (cost/benefjt ratio) ◮ Successively merge child chains increasing in ranks ◮ Resolve contradictory sequences in child chains by merging them into a single node
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IKKBZ
A B E F C D A B E F C D
3/ 10 6/ 10 9/ 10 4/ 10 3/ 10
A B E,F C D
3/ 10 6/ 10 9/ 10 7/ 10
A B C E,F D
3/ 10 6/ 10 9/ 10 7/ 10
◮ Build precedence graph (here rooted in A) ◮ Resolve contradictory sequences in child chains by merging them into a single node rank(E) > rank(F), but E has to precede F ◮ Merge child chains increasing in the nodes rank rank(C) < rank(E,F) < rank(D)
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Search Space Linearization
A B E F C D A B C E F D Query Graph Linearized Search Space ◮ Repeat this for each relation ◮ Guarantee: Final plan at least as good as the best left-deep plan
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Adaptive Optimization – Achievements (SIGMOD 2018)
◮ Solve easy cases optimally ◮ Search Space Linearization: near-optimal plans for common queries ◮ Gracefully tune down plan quality for the most complex queries ◮ Optimize queries on hundreds of relations in the blink of an eye
10 200 400 600 800 1,000 20 40 60
DBMS A DBMS B PostgreSQL adaptive relations median optimization time [s]
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Adaptive Optimization of Very Large Join Queries (SIGMOD 2018)
Query easy? 10K DP entries? corner case? medium? medium? search space linearization search space linearization solve optimally gracefully introduce greediness to keep
- ptimization time
reasonable cannot linearize GOO/DPhyp yes no yes no yes yes no no DPhyp LinDP++ GOO/linDP
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Non-Inner Joins – More Than a Corner Case
◮ Tableau (DBTEST 2018): 20% of the queries involve outer joins, up to 247 in a single query ◮ Others also report signifjcant numbers of queries with outer joins ◮ Non-Inner joins impose reordering constraints ◮ Expressed using hyperedges (Moerkotte et al. SIGMOD 2013)
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Non-Inner Joins – Search Space Linearization?
◮ IKKBZ only handles regular graphs ◮ Still: Given a proper linearization, polynomial time construction of bushy plan ◮ How to extend IKKBZ to generate linearizations for hypergraphs?
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Precedence for Hypergraphs
A B C E F D ◮ Hyperedge {C,D} – {E} ◮ Backward and forward hyperedges
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Precedence for Hypergraphs – Backward Hyperedges
A B C E F D B A C D E F ◮ Precedence DAG, multiple relations have to precede ◮ During merge: Ensure all precedence constraints are satisfjed
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Precedence for Hypergraphs – Forward Hyperedges
A B C E F D E C,B,D A F ◮ Join towards multiple relations, no left deep solution ◮ Recursively linearize group {C,D}: C,B,D ◮ Guarantee: Final plan at least as good as the best left-deep plan if there exists one
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Experiments
◮ More than 10 difgerent join ordering algorithms ◮ 60 seconds timeout per query ◮ Standard benchmarks (TPC-H, TPC-DS, etc.) easily optimized by full DP ⇒ 1,000 realistic random tree queries
◮ Up to 100 relations each ◮ Random reordering constraints
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Plan Quality
◮ Cost normalized to the best known plan per query ◮ LinDP++ generates clearly superior plans
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Optimization Time
◮ Pure inner join queries vs. queries with outer joins
30 60 90 120 10 20 30 40 50 60 70 80 90 100 Query Size (number of relations) Optimization Time [ms]
Algorithm
linearized DP LinDP++
◮ LinDP++ handles non-inner joins as fast as inner joins
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Adaptive Optimization of Very Large Join Queries (SIGMOD 2018)
Query easy? 10K DP entries? corner case? medium? medium? search space linearization search space linearization solve optimally gracefully introduce greediness to keep
- ptimization time
reasonable cannot linearize GOO/DPhyp yes no yes no yes yes no no DPhyp LinDP++ GOO/LinDP++
◮ For performance and correctness reasons: Do not consider crossproducts
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Do Not Consider Crossproducts
- 1. Performance
◮ Exponential search space regardless of the query’s structure ◮ Most considered crossproducts will not reduce cost (A B ∈ O(|A||B|))
- 2. Correctness
◮ Crossproducts in the presence of non-inner joins can yield wrong query results
A D C B A B C D ≡ D C A B A C D B
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Do Not Consider Crossproducts
- 1. Performance
◮ Exponential search space regardless of the query’s structure ◮ Most considered crossproducts will not reduce cost (A B ∈ O(|A||B|))
- 2. Correctness
◮ Crossproducts in the presence of non-inner joins can yield wrong query results
A D C B A B C D D C A B ≡ A C D B
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Do Consider Some Crossproducts
◮ Observation: Some plans would signifjcantly benefjt from crossproducts ◮ TPC-DS: Crossproducts improve geometric mean of cost by 15% ◮ However: 82% of the queries do not benefjt at all from crossproducts ◮ Thus: Do consider some crossproducts (ideally the important ones) ◮ How to effjciently discover the valid and important crossproducts?
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Crossproducts
◮ Intuitively: Crossproduct to avoid massive intermediate results ◮ That is: Bypass expensive joins ◮ Idea: Check neighboring inner joins for opportunities D1 F D2
10 10M 4
F D1 D2
10M 10M
F D2 D1
10M 10M
D1 D2 F
40 10M
◮ If crossproduct is smaller than both intermediate results: Add explicit edge to the query graph
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Cost Improvement
TPC-DS LDBC JOB 25 50 75 100 0 25 50 75 100 0 25 50 75 100 4 8 12 Percentile Cost Improvement Factor
Crossproducts
None All Heuristic
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Optimization Overhead
Algorithm TPC-H TPC-DS LDBC JOB SQLite LinDP++ 8% 6% 8% DPhyp 12% 2.8X 76% All Crossproducts 2.4X 214X 53X 83X 152X ◮ LinDP++ effjciently considers most of the relevant crossproducts
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LinDP++
Optimize as fast as pure inner join queries Efficiently consider promising crossproducts
30 60 90 120 10 20 30 40 50 60 70 80 90 100 Query Size (number of relations) Optimization Time [ms]
Algorithm
linearized DP LinDP++
Generate significantly better plans
TPC-DS LDBC JOB 25 50 75 100 0 25 50 75 100 0 25 50 75 100 4 8 12 Percentile Cost Improvement Factor
Crossproducts
None All Heuristic
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Bonus Slides
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