Fixing memory leak due to HoodieLogFileReader holding on to a logblock #346
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n3nash
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Mar 14, 2018
n3nash
commented
- Removed inMemory HashMap usage in merge(..) code in LogScanner
- Removed inMemory HashMap usage in merge(..) code in LogScanner
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@n3nash can you help me understand where the long lived block is held? both places look like temporary allocations to me..
| HoodieAvroDataBlock dataBlock) throws IOException { | ||
| // TODO (NA) - Instead of creating a new HashMap use the spillable map | ||
| Map<String, HoodieRecord<? extends HoodieRecordPayload>> recordsFromLastBlock = Maps |
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This intermediate map was causing the issue? I guess we don't need this anymore given we are lazy reading the metadata and the content is only read when we are sure we want to merge?
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2 issues. This one is just extra overhead which we don't need and cannot afford. So yes, we merge only when we are sure so this is not needed.
| @@ -56,7 +56,6 @@ | |||
| private static final byte[] oldMagicBuffer = new byte[4]; | |||
| private static final byte[] magicBuffer = new byte[6]; | |||
| private final Schema readerSchema; | |||
| private HoodieLogBlock nextBlock = null; | |||
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does this cause additional memory overhead?
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For this issue. The following is my analysis. Essentially, we pass an inputstream from HoodieLogFileReader to the LogBlocks. An inputstream can be shared in more than 1 logblock. A list of logBlocks are kept until they are merged. So until all logblocks holding the inputstream generated in HoodieLogFileReader are GC'd, they will continue to hold memory. So the last block read is kept in this variable nextBlock and so till the HoodieLogFileReader instance in GC'd this will cause memory overhead.
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Per the screenshot in the ticket, most retained memory comes from private List<IndexedRecord> records; in the AvroDataBlock and not the inputStream itself? The inputstream being held does not seem to have causing these issues..
This might be just a large data block being loaded into memory?
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But I think we will hold onto the last block in each file and that's what you are seeing..
