[IGNITE-6930] Optionally to do not write free list updates to WAL

• Type: Task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.8
• Component/s: cache
• Labels: IEP-8 performance
• Ignite Flags: Release Notes Required
• Assignee: Aleksey Plekhanov
• Reporter: Vladimir Ozerov
• Created: 16/Nov/17 11:21
• Updated: 13/Jan/20 14:30
• Resolved: 14/Oct/19 17:36

Description

When cache entry is created, we need to write update the free list. When entry is updated, we need to update free list(s) several times. Currently free list is persistent structure, so every update to it must be logged to be able to recover after crash. This may incur significant overhead, especially for small entries.

E.g. this is how WAL for a single update looks like. "D" - updates with real data, "F" - free-list management:

 1. [D] DataRecord [writeEntries=[UnwrapDataEntry[k = key, v = [ BinaryObject [idHash=2053299190, hash=1986931360, typeId=-1580729813]], super = [DataEntry [cacheId=94416770, op=UPDATE, writeVer=GridCacheVersion [topVer=122147562, order=1510667560607, nodeOrder=1], partId=0, partCnt=4]]]], super=WALRecord [size=0, chainSize=0, pos=null, type=DATA_RECORD]]
 2. [F] PagesListRemovePageRecord [rmvdPageId=0001000000000005, pageId=0001000000000006, grpId=94416770, super=PageDeltaRecord [grpId=94416770, pageId=0001000000000006, super=WALRecord [size=37, chainSize=0, pos=null, type=PAGES_LIST_REMOVE_PAGE]]]
 3. [D] DataPageInsertRecord [super=PageDeltaRecord [grpId=94416770, pageId=0001000000000005, super=WALRecord [size=129, chainSize=0, pos=null, type=DATA_PAGE_INSERT_RECORD]]]
 4. [F] PagesListAddPageRecord [dataPageId=0001000000000005, super=PageDeltaRecord [grpId=94416770, pageId=0001000000000008, super=WALRecord [size=37, chainSize=0, pos=null, type=PAGES_LIST_ADD_PAGE]]]
 5. [F] DataPageSetFreeListPageRecord [freeListPage=281474976710664, super=PageDeltaRecord [grpId=94416770, pageId=0001000000000005, super=WALRecord [size=37, chainSize=0, pos=null, type=DATA_PAGE_SET_FREE_LIST_PAGE]]]
 6. [D] ReplaceRecord [io=DataLeafIO[ver=1], idx=0, super=PageDeltaRecord [grpId=94416770, pageId=0001000000000004, super=WALRecord [size=47, chainSize=0, pos=null, type=BTREE_PAGE_REPLACE]]]
 7. [F] DataPageRemoveRecord [itemId=0, super=PageDeltaRecord [grpId=94416770, pageId=0001000000000005, super=WALRecord [size=30, chainSize=0, pos=null, type=DATA_PAGE_REMOVE_RECORD]]]
 8. [F] PagesListRemovePageRecord [rmvdPageId=0001000000000005, pageId=0001000000000008, grpId=94416770, super=PageDeltaRecord [grpId=94416770, pageId=0001000000000008, super=WALRecord [size=37, chainSize=0, pos=null, type=PAGES_LIST_REMOVE_PAGE]]]
 9. [F] DataPageSetFreeListPageRecord [freeListPage=0, super=PageDeltaRecord [grpId=94416770, pageId=0001000000000005, super=WALRecord [size=37, chainSize=0, pos=null, type=DATA_PAGE_SET_FREE_LIST_PAGE]]]
10. [F] PagesListAddPageRecord [dataPageId=0001000000000005, super=PageDeltaRecord [grpId=94416770, pageId=0001000000000006, super=WALRecord [size=37, chainSize=0, pos=null, type=PAGES_LIST_ADD_PAGE]]]
11. [F] DataPageSetFreeListPageRecord [freeListPage=281474976710662, super=PageDeltaRecord [grpId=94416770, pageId=0001000000000005, super=WALRecord [size=37, chainSize=0, pos=null, type=DATA_PAGE_SET_FREE_LIST_PAGE]]]

If you sum all space required for operation (size in p.3 is shown incorrectly here), you will see that data update required ~300 bytes, so do free list update!

Proposed solution
1) Optionally do not write free list updates to WAL
2) In case of node restart we start with empty free lists, so data inserts will have to allocate new pages
3) When old data page is read, add it to the free list
4) Start a background thread which will iterate over all old data pages and re-create the free list, so that eventually all data pages are tracked.

Issue Links

• causes: IGNITE-12530 Pages list caching can cause IgniteOOME when checkpoint is triggered by "too many dirty pages" reason
• causes: IGNITE-12442 Fix unnecessary synchronized on PagesCache#add.
• links to: GitHub Pull Request #6893