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  1. WiredTiger
  2. WT-6453

Pin transaction ids for history store cursor operations

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    Details

    • Type: Bug
    • Status: Closed
    • Priority: Major - P3
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: WT3.2.2, 4.5.1, 4.4.0-rc12
    • Component/s: None
    • Labels:
      None
    • Story Points:
      5
    • Sprint:
      Storage - Ra 2020-06-29, Storage - Ra 2020-07-13

      Description

      We've seen an issue where we hit a segfault when walking an update chain for a history store key. The pointer that we try to dereference has a magic value 0xcdcdcdcdcdcdcdcd which is something that TCMalloc uses when deallocating (I don't know the specifics but there is a code chunk showing this magic here).

      I think the fact that we ignore tombstones in history store is suspicious because it may cause us to look past an update that we usually wouldn't. I do see that we return a tombstone if it is globally visible, however (which means we're not going to be looking past globally visible updates).

      GDB output:

      (gdb) bt
      #0  __wt_txn_read_upd_list (session=0x7fedf77a97c0, cbt=0x7fedf4e18da0, upd=0xcdcdcdcdcdcdcdcd, prepare_updp=0x0)
          at src/third_party/wiredtiger/src/include/txn.i:849
      #1  0x00007fee00c7288e in __cursor_row_prev (skippedp=<synthetic pointer>, restart=<optimized out>, newpage=<optimized out>, cbt=0x7fedf4e18da0)
          at src/third_party/wiredtiger/src/btree/bt_curprev.c:517
      #2  __wt_btcur_prev (cbt=cbt@entry=0x7fedf4e18da0, truncating=truncating@entry=false) at src/third_party/wiredtiger/src/btree/bt_curprev.c:657
      #3  0x00007fee00c7c0aa in __wt_btcur_search_near (cbt=cbt@entry=0x7fedf4e18da0, exactp=exactp@entry=0x7fedf1f1c174)
          at src/third_party/wiredtiger/src/btree/bt_cursor.c:691
      #4  0x00007fee00bc5d00 in __curfile_search_near (cursor=0x7fedf4e18da0, exact=0x7fedf1f1c174)
          at src/third_party/wiredtiger/src/cursor/cur_file.c:231
      #5  0x00007fee00be2a5e in __hs_delete_key_from_ts_int (ts=0, key=0x7fedc0437c80, btree_id=46, session=0x7fedf77a97c0)
          at src/third_party/wiredtiger/src/history/hs.c:1313
      #6  __wt_hs_delete_key_from_ts (session=session@entry=0x7fedf77a97c0, btree_id=46, key=0x7fedc0437c80, ts=ts@entry=0)
          at src/third_party/wiredtiger/src/history/hs.c:1378
      #7  0x00007fee00d39ed3 in __wt_rec_row_leaf (session=session@entry=0x7fedf77a97c0, r=r@entry=0x7fedc2eed420,
          pageref=pageref@entry=0x7fedc1e53fe0, salvage=salvage@entry=0x0) at src/third_party/wiredtiger/src/reconcile/rec_row.c:871
      #8  0x00007fee00c15fb5 in __reconcile (page_lockedp=<synthetic pointer>, flags=172, salvage=0x0, ref=0x7fedc1e53fe0, session=0x7fedf77a97c0)
          at src/third_party/wiredtiger/src/reconcile/rec_write.c:182
      #9  __wt_reconcile (session=session@entry=0x7fedf77a97c0, ref=ref@entry=0x7fedc1e53fe0, salvage=salvage@entry=0x0, flags=flags@entry=172)
          at src/third_party/wiredtiger/src/reconcile/rec_write.c:89
      #10 0x00007fee00bdda5f in __evict_review (inmem_splitp=<synthetic pointer>, evict_flags=0, ref=0x7fedc1e53fe0, session=0x7fedf77a97c0)
          at src/third_party/wiredtiger/src/evict/evict_page.c:658
      #11 __wt_evict (session=session@entry=0x7fedf77a97c0, ref=ref@entry=0x7fedc1e53fe0, previous_state=previous_state@entry=3 '\003',
          flags=flags@entry=0) at src/third_party/wiredtiger/src/evict/evict_page.c:186
      #12 0x00007fee00bd5e19 in __evict_page (session=0x7fedf77a97c0, is_server=false) at src/third_party/wiredtiger/src/evict/evict_lru.c:2254
      #13 0x00007fee00bd67f5 in __evict_lru_pages (session=session@entry=0x7fedf77a97c0, is_server=is_server@entry=false)
          at src/third_party/wiredtiger/src/evict/evict_lru.c:1134
      #14 0x00007fee00bd8be4 in __wt_evict_thread_run (session=0x7fedf77a97c0, thread=0x7fedfc30c420)
          at src/third_party/wiredtiger/src/evict/evict_lru.c:324
      #15 0x00007fee00c44c89 in __thread_run (arg=0x7fedfc30c420) at src/third_party/wiredtiger/src/support/thread_group.c:31
      #16 0x00007fedfe3a7aa1 in start_thread () from /lib64/libpthread.so.0
      #17 0x00007fedfe0f4c4d in clone () from /lib64/libc.so.6
      (gdb) f 0
      #0  __wt_txn_read_upd_list (session=0x7fedf77a97c0, cbt=0x7fedf4e18da0, upd=0xcdcdcdcdcdcdcdcd, prepare_updp=0x0)
          at src/third_party/wiredtiger/src/include/txn.i:849
      849	        WT_ORDERED_READ(type, upd->type);
      (gdb) p upd
      $1 = (WT_UPDATE *) 0xcdcdcdcdcdcdcdcd
      (gdb) p cbt->ins->upd
      $2 = (WT_UPDATE *) 0x7fedc35c54c0
      (gdb) p *cbt->ins->upd
      $3 = {txnid = 133879, durable_ts = 0, start_ts = 0, next = 0x7fedc17dd3e0, size = 0, type = 4 '\004', prepare_state = 0 '\000',
        flags = 0 '\000', data = 0x7fedc35c54e7 "'"}
      (gdb) p *cbt->ins->upd->next
      $4 = {txnid = 133862, durable_ts = 0, start_ts = 0, next = 0x0, size = 74, type = 3 '\003', prepare_state = 0 '\000', flags = 0 '\000',
        data = 0x7fedc17dd407 "\200\200\203G"}
      

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              Assignee:
              alex.cameron Alex Cameron
              Reporter:
              alex.cameron Alex Cameron
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                Created:
                Updated:
                Resolved: