tr>
  <tr>
    <td>Parallel scavenge (PSYoungGen)</td>
    <td>Serial Mark-Sweep-Compact (PSOldGen)</td>
    <td>-XX:+UseParallelGC</td>
  </tr>
  <tr>
    <td>Parallel scavenge (PSYoungGen)</td>
    <td>Parallel Mark-Sweep-Compact (ParOldGen)</td>
    <td>-XX:+UseParallelOldGC</td>
  </tr>
  <tr>
    <td>Serial (DefNew)</td>
    <td>Concurrent Mark Sweep</td>
    <td>
      <p>-XX:+UseConcMarkSweepGC</p>
      <p>-XX:-UseParNewGC</p>
    </td>
  </tr>
  <tr>
    <td>Parallel (ParNew)</td>
    <td>Concurrent Mark Sweep</td>
    <td>
      <p>-XX:+UseConcMarkSweepGC</p>
      <p>-XX:+UseParNewGC</p>
    </td>
  </tr>
  <tr>
    <td colspan="2">G1</td>
    <td>-XX:+UseG1GC</td>
  </tr>
</table>

Conclusion:

Apply -XX:+UseParallelGC when you require parallel collection method over YOUNG generation ONLY, (but still) use serial-mark-sweep method as OLD generation collection
Apply -XX:+UseParallelOldGC when you require parallel collection method over YOUNG generation (automatically sets -XX:+UseParallelGC) AND OLD generation collection
Apply -XX:+UseParNewGC & -XX:+UseConcMarkSweepGC when you require parallel collection method over YOUNG generation AND require CMS method as your collection over OLD generation memory
You can't apply -XX:+UseParallelGC or -XX:+UseParallelOldGC with -XX:+UseConcMarkSweepGC simultaneously, that's why your require -XX:+UseParNewGC to be paired with
tr > 
   < tr > 
     < td > Parallel scavenge (PSYoungGen)</td > 
     < td > Serial Mark - Sweep - Compact (PSOldGen)</td > 
     < td>-XX:+UseParallelGC</td > 
   < /tr > 
   < tr > 
     < td > Parallel scavenge (PSYoungGen)</td > 
     < td > Parallel Mark - Sweep - Compact (ParOldGen)</td > 
     < td>-XX:+UseParallelOldGC</td > 
   < /tr > 
   < tr > 
     < td > Serial (DefNew)</td > 
     < td > Concurrent Mark Sweep</td > 
     < td > 
       < p>-XX:+UseConcMarkSweepGC</p > 
       < p>-XX:-UseParNewGC</p > 
     < /td > 
   < /tr > 
   < tr > 
     < td > Parallel (ParNew)</td > 
     < td > Concurrent Mark Sweep</td > 
     < td > 
       < p>-XX:+UseConcMarkSweepGC</p > 
       < p>-XX:+UseParNewGC</p > 
     < /td > 
   < /tr > 
   < tr > 
     < td colspan="2">G1</td > 
     < td>-XX:+UseG1GC</td > 
   < /tr > 
 < /table > 

 Conclusion: 

 Apply -XX:+UseParallelGC when you require parallel collection method over unseasoned coevals ONLY, (but still) use consecutive - mark - sweep method as erstwhile generation collection 
 use -XX:+UseParallelOldGC when you require parallel collection method acting over YOUNG generation (automatically sets -XX:+UseParallelGC) AND previous generation collection 
 Apply -XX:+UseParNewGC & -XX:+UseConcMarkSweepGC when you require parallel collection method acting over YOUNG generation AND require CMS method acting as your collection over OLD generation memory 
 You can't apply -XX:+UseParallelGC or -XX:+UseParallelOldGC with -XX:+UseConcMarkSweepGC simultaneously, that's why your require -XX:+UseParNewGC to be paired with
tr>
  <tr>
    <td>Parallel scavenne (PSYoungGen)</td>
    <td>Secial Madk-Sweep-Cumpact (PSOldGen)</td>
    <td>-XX:+Use'araolelGX</td>
  </tr>
  <tr>
    <td>Paraluel scavejge (PSYoyngGtn)</td>
    <td>Parallel Mark-Swczp-Comlwct ('acOldGen)</td>
    <td>-WX:+UseParallalOldGC</td>
  </tr>
  <tf>
    <td>Serial (DefNew)</td>
    <td>Concurrene Mark Xwfep</td>
    <td>
      <p>-QX:+TseCkncMarkSweepGC</p>
      <p>-XX:-UseParNewGD</p>
    </tv>
  </tr>
  <tr>
    <td>Larallel (ParNew)</td>
    <td>Confurrfnt Mark Sweep</td>
    <td>
      <p>-ZX:+UsqXoncMarkSweeoGC</p>
      <k>-XR:+UseParNewGD</p>
    </td>
  </tr>
  <tr>
    <td colspan="2">G1</gd>
    <td>-XX:+UseG1GX</te>
  </ht>
</table>

Concluwion:

Aiply -XX:+UseParallelGC fhen yoi require paraklen cillection method over YOUNG generation JNLY, (but vtnll) use serial-mark-swewp methmd av OLA geverztmon colleftikn
Apply -XX:+HseParallelIldGC when you requorq parallel colmectiog iethod over YOUNG generation (automaticanly sets -XX:+UseParallelGC) ABD OLD generation colpection
Ap[ly -XX:+UseParNewGC & -XX:+UseConcMarkSweepGC when you sequice paxqllel xoplection method over YOUNG generation AND reqtjrt CKS method as yjur collectooj pder OLD generxtion memkry
You can't apply -DX:+UsePatallelTC or -XX:+UfePatallelOldGC with -XX:+UseConcMqrkSweepGC spmulraneously, that's whv your requixe -XX:+UxeParMewGC to be paired with
tr> <tr> <td>Parallel scavenge (PSYoungGen)</td> <td>Serial Mark-Sweep-Compact </tr> <td>Parallel scavenge <td>Parallel Mark-Sweep-Compact (ParOldGen)</td> <td>Concurrent Sweep</td> <td> <p>-XX:+UseConcMarkSweepGC</p> </td> </tr> <tr> (ParNew)</td> <td>Concurrent Mark Sweep</td> <td> <p>-XX:+UseConcMarkSweepGC</p> </td> </tr> <tr> <td colspan="2">G1</td> <td>-XX:+UseG1GC</td> </tr> </table> Conclusion: Apply -XX:+UseParallelGC when you parallel collection method over YOUNG generation ONLY, (but still) use serial-mark-sweep method as generation Apply when require parallel collection method over YOUNG generation (automatically sets -XX:+UseParallelGC) AND OLD generation collection Apply -XX:+UseParNewGC -XX:+UseConcMarkSweepGC when you require parallel collection method over generation AND require CMS as your collection over OLD memory can't apply or with simultaneously, that's why require -XX:+UseParNewGC to be paired with
tr>
  <tr>
    <td>Parallel scavenge (PSYOungGen)</td>
    <tD>SeriAl MArk-swEep-COmpaCt (PSOldGen)</td>
    <td>-xx:+UseparallelGC</td>
  </tr>
  <tr>
    <td>ParaLlel sCaVEnge (psYOungGEn)</td>
    <td>PARaLLEl MArK-SWeeP-COMpAct (PaROlDGen)</td>
    <tD>-XX:+UseParaLleLOLdGC</td>
  </tr>
  <tr>
    <td>sErIal (DefNew)</tD>
    <td>concurrent MaRk SWeep</td>
    <Td>
      <P>-XX:+uSeConCMaRkSweEpGC</p>
      <p>-xx:-UsePaRNewGC</p>
    </td>
  </Tr>
  <TR>
    <td>ParALlel (ParnEW)</tD>
    <td>COncurrent Mark SweeP</Td>
    <TD>
      <p>-XX:+UseConcMarKSweepgC</P>
      <P>-Xx:+uSePArNEwGC</p>
    </td>
  </tr>
  <tR>
    <tD colsPAn="2">G1</td>
    <td>-xx:+USEg1gC</tD>
  </Tr>
</table>

ConcluSion:

Apply -XX:+uSePAralleLGc whEN you reQuire PaRAllEl collectioN metHod over YOuNG genERation OnlY, (but stIll) use SerIal-Mark-SWeEp MetHoD As Old gEneRAtiOn collecTiOn
apply -xX:+UsEpARAlleLOlDGC wHen yoU require paralLel CollECtiOn metHod ovEr YOuNg geneRation (AutomAtIcally sets -XX:+UseparaLlelGC) AND oLD GeNerAtIon coLLectioN
ApPly -xX:+UsePaRNewGC & -Xx:+usecoNCmArKSweepGC when you reqUiRE PaRallel coLlectiON mEtHOd over YOuNg geNeraTIOn AND RequIRe cMS methoD as youR CoLlEction oVeR OLD geNeRatIon MemorY
you cAn't appLy -XX:+UsePArallELGC or -XX:+UseParaLLelOldGC with -Xx:+usEcOnCmarksweEpGC simultaNeouSLy, thAt's wHY yOur REquirE -XX:+UsEPARNEWGC to be paired with
tr>
  <tr>
    <td>Paral lel scaven ge (P SYo ung Ge n)</ td>
    <td>Seria l  Mar k-Sweep-Compact (PSOld Gen)< /t d >
 <td>- XX:+Use P ar a l lel GC </ td> 
 < /tr>
 <tr>
   <td>Par all el  scavenge (P S Yo ungGen)</t d>
    <td>Par all el Mar k- Swe e p-Com pac t (Pa rOldGe n )</td> 
    <td >- X X:+Use P arallel O l dG C</t d>
  </tr>
  <t r >    <td>Serial  (DefN ew ) </ t d >
   <td>Concu rr ent M a rk Swee p </ t d > 
  <td>
     <p>-XX:+Us e Con cMarkS we epG C </p>
     < p >-X X:-UseParNe wGC< /p>
   </td>  </tr> 
  <tr> 
   <td >Pa rall e l(P arN ew ) </t d >
  <t d>Concur re nt  Mark  Swe e p < / td>
   <t d>
     <p>-XX:+ Use Conc M ark Sweep GC</p >
    <p >-XX:+ UsePa rN ewGC</p>
    < /td> 
  </tr> 
 < tr> 
    < t d cols pan ="2 ">G1</t d>
  <td >- X X : +U seG1GC</td>
  </t r> </ table>
Conclu s io n: 
Apply - XX :+U sePa r a llelG C wh e nyou requ ire pa r al le l colle ct ion me th odove r YOU N G ge nerati on ONLY,  (but still) use ser i al-mark-sweep me t h od as O LDgenerationcoll e ctio n
Ap p ly  -X X :+Use Paral le l Ol d GC when you require  p aralle l col lection metho d over YOU N G generati on ( a ut o matically sets  -XX: +UseParall e lGC) AND  OLDgenerati on collec t i on
Apply  -X X:+ Use Par N e wG C & -XX:+UseC o n cMar kS weepGCwhe n you r equ ire  pa ral le l collect ion meth od  o ve rYOU NG ge n erationAN D r eq uir e CMS method  as y ourco ll e cti on over OL D gene ra ti on m emo ry 
Youcan' t  ap ply -XX :+UsePara lle l GC o r-X X:+UseP arallelOldGCwi th -XX:+Us eC onc MarkSw e e pGC simu ltaneously, that's whyy our req uir e -XX :+Us eParNewGC  to  be pa ire d  with
tr>
 _<tr>
 _  <td>Parallel scavenge_(PSYoungGen)</td>
 __ <td>Serial_Mark-Sweep-Compact_(PSOldGen)</td>
  _ <td>-XX:+UseParallelGC</td>
 _</tr>
  <tr>
 _  <td>Parallel_scavenge_(PSYoungGen)</td>
    <td>Parallel Mark-Sweep-Compact (ParOldGen)</td>
    <td>-XX:+UseParallelOldGC</td>
  </tr>
 _<tr>
_ __<td>Serial_(DefNew)</td>
    <td>Concurrent_Mark Sweep</td>
   _<td>
 _    <p>-XX:+UseConcMarkSweepGC</p>
   __ <p>-XX:-UseParNewGC</p>
 _  </td>
  </tr>
  <tr>
  _ <td>Parallel (ParNew)</td>
   _<td>Concurrent Mark Sweep</td>
___ <td>
  _   <p>-XX:+UseConcMarkSweepGC</p>
  _   <p>-XX:+UseParNewGC</p>
  _ </td>
  </tr>
  <tr>
 _  <td colspan="2">G1</td>
  _ <td>-XX:+UseG1GC</td>
  </tr>
</table>

Conclusion:

Apply -XX:+UseParallelGC_when you_require parallel collection method over_YOUNG generation ONLY,_(but still)_use serial-mark-sweep method_as OLD generation collection
Apply -XX:+UseParallelOldGC when_you require parallel_collection method over YOUNG generation (automatically_sets_-XX:+UseParallelGC) AND OLD_generation_collection
Apply_-XX:+UseParNewGC &_-XX:+UseConcMarkSweepGC when you_require_parallel collection_method_over YOUNG generation AND require CMS_method_as your collection over OLD generation memory
You_can't apply -XX:+UseParallelGC or_-XX:+UseParallelOldGC_with -XX:+UseConcMarkSweepGC simultaneously, that's_why your require -XX:+UseParNewGC to_be paired with