keithbostic I'm going to assign this to you because the appearance of an error from fopen coincides with the merge of your recent changes with this job. Unfortunately, because this is sanitizer, there is no core dump. So this is all we have. I'll attempt repro.
[1427093837:401924][92396:0x7fa48f9f1700], t, statlog-server: RUNDIR/WiredTigerStat.23.17: fopen: No such file or directory [1427093837:401974][92396:0x7fa48f9f1700], t, statlog-server: statistics log server error: No such file or directory t: cursor.insert[1427093837:401989][92396:0x7fa48f9f1700], t, statlog-server: the process must exit and restart: WT_PANIC: WiredTiger library panic : WT_PANIC: WiredTiger library panic [1427093837:402019][92396:0x7fa48f9f1700], t, statlog-server: aborting WiredTiger library
http://build.wiredtiger.com:8080/job/wiredtiger-test-format-stress-sanitizer/2998
############################################ # RUN PARAMETERS ############################################ abort=0 auto_throttle=1 firstfit=1 bitcnt=5 bloom=1 bloom_bit_count=20 bloom_hash_count=10 bloom_oldest=1 cache=85 checkpoints=1 checksum=uncompressed chunk_size=8 compaction=0 compression=zlib data_extend=0 data_source=file delete_pct=28 dictionary=0 evict_max=3 file_type=variable-length column-store backups=0 huffman_key=0 huffman_value=0 insert_pct=29 internal_key_truncation=1 internal_page_max=9 isolation=read-committed key_gap=11 key_max=88 key_min=30 leak_memory=0 leaf_page_max=17 logging=0 logging_archive=1 logging_prealloc=0 lsm_worker_threads=3 merge_max=16 mmap=1 ops=100000 prefix_compression=1 prefix_compression_min=6 repeat_data_pct=35 reverse=1 rows=100000 runs=1 split_pct=78 statistics=0 statistics_server=1 threads=32 timer=20 value_max=139 value_min=10 wiredtiger_config= write_pct=28 ############################################