CRT-P0001 · Multiple `append` can be combined into a single call

Multiple append can be combined into a single call CRT-P0001

Performance

Major

8 months ago — 4 years old

can combine chain of 2 appends into one

pkg/schedule/schedulers/hot_region_v2_test.go

443	for i := 10; i < 50; i++ {
444		regions = append(regions, testRegionInfo{uint64(i), []uint64{1, 2, 3}, smallHotPeerByte, 0, smallHotPeerQuery})
445		if i < 20 {
446			regions = append(regions, testRegionInfo{uint64(i), []uint64{2, 1, 3}, smallHotPeerByte, 0, smallHotPeerQuery})447			regions = append(regions, testRegionInfo{uint64(i), []uint64{3, 1, 2}, smallHotPeerByte, 0, smallHotPeerQuery})
448		}
449	}

can combine chain of 2 appends into one

pkg/tso/keyspace_group_manager_test.go

1012
1013	events := []*etcdEvent{}
1014	// Split target keyspace group event arrives first.
1015	events = append(events, generateKeyspaceGroupPutEvent(2, []uint32{2} /* Mock 2 replicas */, []string{svcAddr, svcAddr}, &endpoint.SplitState{1016		SplitSource: 1,
1017	}))
1018	// Split source keyspace group event arrives later.

can combine chain of 11 appends into one

pkg/tso/keyspace_group_manager_test.go

 291	events := []*etcdEvent{}
 292	// Assign keyspace group 0 to this host/pod/keyspace-group-manager.
 293	// final result: assigned [0], loaded [0]
 294	events = append(events, generateKeyspaceGroupPutEvent(0, []uint32{0}, []string{svcAddr})) 295	// Assign keyspace group 1 to this host/pod/keyspace-group-manager.
 296	// final result: assigned [0,1], loaded [0,1]
 297	events = append(events, generateKeyspaceGroupPutEvent(1, []uint32{1}, []string{"unknown", svcAddr}))

can combine chain of 3 appends into one

pkg/unsaferecovery/unsafe_recovery_controller.go

 270				reported += str
 271			}
 272		}
 273		status.Details = append(status.Details, "Stores that have not dispatched plan: "+strings.Trim(undispatched, ", ")) 274		status.Details = append(status.Details, "Stores that have reported to PD: "+strings.Trim(reported, ", "))
 275		status.Details = append(status.Details, "Stores that have not reported to PD: "+strings.Trim(unreported, ", "))
 276	} else {

can combine chain of 11 appends into one

pkg/schedule/plan/balance_plan_test.go

227func (suite *balanceSchedulerPlanAnalyzeTestSuite) TestAnalyzerResult5() {
228	re := suite.Require()
229	plans := make([]Plan, 0)
230	plans = append(plans, &BalanceSchedulerPlan{Source: suite.stores[4], Step: 0, Status: NewStatus(StatusStoreRemoveLimitThrottled)})231	plans = append(plans, &BalanceSchedulerPlan{Source: suite.stores[3], Region: suite.regions[0], Step: 1, Status: NewStatus(StatusRegionNotMatchRule)})
232	plans = append(plans, &BalanceSchedulerPlan{Source: suite.stores[2], Region: suite.regions[0], Step: 1, Status: NewStatus(StatusRegionNotMatchRule)})
233	plans = append(plans, &BalanceSchedulerPlan{Source: suite.stores[1], Target: suite.stores[0], Step: 2, Status: NewStatus(StatusStoreScoreDisallowed)})

Description

Multiple calls for append could be combined into a single call for append.

The append built-in function appends elements to the end of a slice. If it has sufficient capacity, the destination is resliced to accommodate the new elements, but if capacity is not enough, then append will allocate a new underlying array and return the updated slice. Therefore, it is necessary to store the result of append, often in the variable holding the slice itself. Appending calls in a single call of append allocates memory just once to accommodate all the elements to be appended. Whereas multiple calls to append introduce many overheads, most notably being the possibility of more calls for memory allocation because the total number of elements to be appended over multiple calls of append is unknown beforehand, resulting in inaccurate preallocation.

Read more about a similar implementation for append. Hence, a single call to append is recommended.

Bad practice

xs = append(xs, 1)
xs = append(xs, 2)
xs = append(xs, 3)
xs = append(xs, 4)
xs = append(xs, 5)

tikv / pd

Bad practice

Recommended