executor: introduce Allocator to manage memory used by executors
#10580
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/rebuild |
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Here are the sysbench results. I have tested two rounds with The first round: after: avg(before) = 852.22, The second round: after: avg(before) = 846.166, |
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/rebuild |
tiancaiamao
reviewed
May 31, 2019
| @@ -84,6 +84,7 @@ type baseExecutor struct { | |||
| children []Executor | |||
| retFieldTypes []*types.FieldType | |||
| runtimeStats *execdetails.RuntimeStats | |||
| allocator chunk.Allocator | |||
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Why we need to store it into executor? we can always get if from ctx.SessionVars()
| @@ -908,6 +910,7 @@ func (e *SelectionExec) Open(ctx context.Context) error { | |||
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| // Close implements plannercore.Plan Close interface. | |||
| func (e *SelectionExec) Close() error { | |||
| e.childResult.Release() | |||
| e.childResult = nil | |||
| e.selected = nil | |||
| return e.baseExecutor.Close() | |||
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How about put the Release() to the baseExecutor.Close() ?
It's easy to leak resource if we have to add Release() in every executor...
| @@ -0,0 +1,247 @@ | |||
| package chunk | |||
| type Allocator interface { | ||
| Alloc(l, c int) []byte | ||
| Free(buf []byte) | ||
| SetParent(a Allocator) |
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What's the purpose of SetParent ?
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| // Free releases memory. | ||
| func (b *multiBufChan) Free(buf []byte) { | ||
| b.allocators[atomic.AddUint32(&b.freeIndex, 1)%b.numAllocators].Free(buf) |
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The buffer from one allocator would be give back to another one?
| pad = make([]byte, (1<<uint(capIndexBit))+1) | ||
| ) | ||
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| func getCapIndex(bitN uint) ([]int, []int) { |
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Any comment to explain this function?
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| type bufChan struct { | ||
| maxCap int | ||
| bufList []chan []byte |
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This struct create too many small objects and bad for GC
| // Close closes this allocator. | ||
| func (b *bufChan) Close() { | ||
| for _, ch := range b.bufList { | ||
| for len(ch) > 0 { |
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for _, buf := range ch {
...
}
| for _, ch := range b.bufList { | ||
| for len(ch) > 0 { | ||
| buf := <-ch | ||
| b.parent.Free(buf) |
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Will the buf return to a Closed allocator, taking concurrency into consideration?
| col.elemBuf = nil | ||
| } else { | ||
| col.elemBuf = a.Alloc(elemLen, elemLen) | ||
| col.data = a.Alloc(0, cap*elemLen) |
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During the usage of the chunk, the data/elemBuf/nullBitmap will grow atomically and it's improper to return the memory to the allocator...
c.nullBitmap = append(c.nullBitmap, b)
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Here is a post about how to recycle memory buffers in Golang. |
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Close it because it increases the complexity of memory management and the 4.5% profit is not worth doing that. |
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What problem does this PR solve?
The first step to fix #9396.
Introduce an
Allocatorto manage memory used by chunk in executors.What is changed and how it works?
Allocator.Allocator.Releasemethod toChunk.Check List
Tests
Side effects