The keys written are (1, number) where it is 1 << 32 | number. The unfortunate thing is that JSON outputs a printable character whenever it can. So, for 1,427260, I see this key in printlog:
"key": "\u00E5\u0001\u0000\u0006\u0084\u00FC",

0x684FC == 427260. When I look at a different value, 427570, I see this key in printlog:
key": "\u00E5\u0001\u0000\u0006\u00862"

It looks like 0x6862, but what it really is (I only know this because I know approximately what values should be there and other keys nearby) is 0x686"2" or 0x68632 == 427570.

It is kind of sad and unfortunate that it is printed that way. In particular, it makes it hard to view and harder to search consistently.

Sue LoVerso, Two approaches I can think of:
1) have a wt printlog option that forces the Unicode escape for everything. For the example you gave:
"key: "\u00E5\u0001\u0000\u0006\u0086\u0062"
"value": "Hello"

2) have a wt printlog option that emits hex in addition to the current way.
"key: "\u00E5\u0001\u0000\u0006\u00862"
"key-hex: "E50100068662"
"value": "Hello"
"value-hex": "48656C6C6F"

I find option two much more readable and usable (you get the printable stuff when you need it, and the hex stuff when you need that).

I think option two will be more usable because then it can be predictably searched. By the time we're printing the contents of the log records, we're searching through it.

Author:

Message: WT-2235. Changes to wt printlog to add -x option and remove -p.

wt printlog -x produces extra "-hex" fields when appropriate. For example,
when printing a "row_put" entry, in addition to "key" and "value" (printed
as JSON strings with Unicode escapes), there will also be "key-hex" and
"key-value" entries in the JSON dictionary, containing a hex dump for each
of these fields.

For consistency with existing WT outputs, all hex output is in lower case.
One visible change is that our Unicode escapes in JSON, also used for
'wt dump j', now produce hex characters in lower case ('a''f'). Before,
'wt dump j' produced upper case hex (using 'A''F').
Branch: develop
https://github.com/wiredtiger/wiredtiger/commit/c19c1a7d5d52d35ab6c7959a6738630fe77a4fa5

Author:

Message: WT-2235. Fix doc synopses for 'wt' to use 'R', not 'r', as the recovery flag.
Branch: develop
https://github.com/wiredtiger/wiredtiger/commit/faa5c92e1098b286ce6b0a1b7f3f49e424d7fb15

Author:

Message: WT-2235. Share an array used for converted binary to hex.
Branch: develop
https://github.com/wiredtiger/wiredtiger/commit/4a225dd68a667b87162e61f0c20b183522419fa0

Author:

Message: Merge pull request #2371 from wiredtiger/wt-2235-printlog-hex

WT-2235. Changes to wt printlog to add -x option and remove -p.
Branch: develop
https://github.com/wiredtiger/wiredtiger/commit/8d4e75d1d00fe44268373fee49ce970c4356e714

Author:

Message: Import wiredtiger-wiredtiger-2.7.0-269-g44463c5.tar.gz from wiredtiger branch mongodb-3.4

ref: 3c2ad56..44463c5

SERVER-21833 Compact does not release space to the system with WiredTiger
WT-2060 Simplify aggregation of statistics
WT-2099 Seeing memory underflow messages
WT-2113 truncate01 sometimes fails
WT-2177 Add a per-thread seed to random number generator
WT-2198 bulk load and column store appends
WT-2231 pinned page cursor searches could check parent keys
WT-2235 wt printlog option without unicode
WT-2245 WTPERF Truncate has no ability to catch up when it falls behind
WT-2246 column-store append searches the leaf page; the maximum record number fails CRUD operations
WT-2256 WTPERFs throttle option fires in bursts
WT-2257 wtperf doesn't handle overriding workload config
WT-2259 __wt_evict_file_exclusive_on() should clear WT_BTREE_NO_EVICTION on error
WT-2260 Workloads evict internal pages unexpectedly
WT-2262 Random sampling is skewed by tree shape
WT-2265 Wiredtiger related change in ppc64le specific code block in gcc.h
WT-2266 Add wtperf config to set if perf thresholds are fatal
WT-2269 wtperf should dump its config everytime it runs
WT-2272 Stress test assertion in the sweep server
WT-2275 broken DB after application crash
WT-2276 tool to decode checkpoint addr
WT-2277 Remove WT check against big-endian systems
WT-2279 Define WT_PAUSE(), WT_FULL_BARRIER(), etc when s390x is defined
WT-2281 wtperf smoke.sh fails on ppc64le
WT-2282 error in wt_txn_update_oldest verbose message test
WT-2283 retry in txn_update_oldest results in a hang
WT-2285 configure should set BUFFER_ALIGNMENT_DEFAULT to 4kb on linux
WT-2289 failure in fast key check
WT-2290 WT_SESSION.compact could be more effective.
WT-2291 Random cursor walk inefficient in skip list only trees
WT-2297 Fix off-by-one error in Huffman config file parsing
WT-2299 upper-level WiredTiger code is reaching into the block manager
WT-2301 Add reading a range to wtperf
WT-2303 Build warning in wtperf
WT-2304 wtperf crash dumping config
WT-2307 Internal page splits can corrupt cursor iteration
WT-2311 Support Sparc
Branch: master
https://github.com/mongodb/mongo/commit/d845b75e5f0837f801bdf371babd985308a1ad80

Author:

Message: Import wiredtiger-wiredtiger-2.7.0-559-g07966a4.tar.gz from wiredtiger branch mongodb-3.2

ref: 3c2ad56..07966a4

WT-1517 schema format edge cases
WT-1801 Add a directory sync after rollback of a WT_SESSION::rename operation
WT-2060 Simplify aggregation of statistics
WT-2073 metadata cleanups
WT-2099 Seeing memory underflow messages
WT-2113 truncate01 sometimes fails
WT-2142 Connection cleanup in Python tests
WT-2177 Add an optional per-thread seed to random number generator
WT-2198 bulk load and column store appends
WT-2216 simplify row-store search loop slightly
WT-2225 New split code performance impact
WT-2231 pinned page cursor searches could check parent keys
WT-2235 wt printlog option without unicode
WT-2242 WiredTiger treats dead trees the same as other trees in eviction
WT-2244 Trigger in-memory splits sooner
WT-2245 WTPERF Truncate has no ability to catch up when it falls behind
WT-2246 column-store append searches the leaf page; the maximum record number fails CRUD operations
WT-2247 variable-length column-store in-memory page splits
WT-2256 WTPERFs throttle option fires in bursts
WT-2257 wtperf doesn't handle overriding workload config
WT-2258 WiredTiger preloads pages even when direct-IO is configured.
WT-2259 __wt_evict_file_exclusive_on() should clear WT_BTREE_NO_EVICTION on error
WT-2260 Workloads evict internal pages unexpectedly
WT-2262 Random sampling is skewed by tree shape
WT-2265 Wiredtiger related change in ppc64le specific code block in gcc.h
WT-2266 Add wtperf config to set if perf thresholds are fatal
WT-2267 Improve wtperf throttling implementation to provide steady load
WT-2269 wtperf should dump its config everytime it runs
WT-2272 Stress test assertion in the sweep server
WT-2275 broken DB after application crash
WT-2276 tool to decode checkpoint addr
WT-2277 Remove WT check against big-endian systems
WT-2279 Define WT_PAUSE(), WT_FULL_BARRIER(), etc when s390x is defined
WT-2281 wtperf smoke.sh fails on ppc64le
WT-2282 error in wt_txn_update_oldest verbose message test
WT-2283 retry in txn_update_oldest results in a hang
WT-2284 Repeated macro definition
WT-2285 configure should set BUFFER_ALIGNMENT_DEFAULT to 4kb on linux
WT-2287 WT_SESSION.rebalance
WT-2289 failure in fast key check
WT-2290 WT_SESSION.compact could be more effective.
WT-2291 Random cursor walk inefficient in skip list only trees
WT-2295 WT_SESSION.create does a full-scan of the main table
WT-2296 New log algorithm needs improving for sync/flush settings
WT-2297 Fix off-by-one error in Huffman config file parsing
WT-2299 upper-level WiredTiger code is reaching into the block manager
WT-2301 Add reading a range to wtperf
WT-2303 Build warning in wtperf
WT-2304 wtperf crash dumping config
WT-2305 Fix coverity scan issues on 23/12/2015
WT-2307 Internal page splits can corrupt cursor iteration
WT-2308 custom extractor for ref_cursors in join cursor
WT-2311 Support Sparc
WT-2312 re-creating a deleted column-store page can corrupt the in-memory tree
WT-2313 sweep-server: conn_dhandle.c, 610: dhandle != conn->cache->evict_file_next
WT-2314 page-swap error handling is inconsistent
WT-2316 stress test failure: WT_CURSOR.prev out-of-order returns
WT-2320 Only check copyright when cutting releases
WT-2321 WT-2321: race between eviction and worker threads on the eviction queue
WT-2326 Change WTPERF to use new memory allocation functions instead of the standard
WT-2328 schema drop does direct unlink, it should use a block manager interface.
WT-2331 Checking of search() result for reference cursors before join()
WT-2332 Bug in logging write-no-sync mode
WT-2333 Add a flag so drop doesn't block
WT-2335 NULL pointer crash in config_check_search with invalid configuration string
WT-2338 Disable using pre-allocated log files when backup cursor is open
WT-2339 format post-rebalance verify failure (stress run #11586)
WT-2340 Add logging guarantee assertions, whitespace
WT-2342 Enhance wtperf to support background create and drop operations
WT-2344 OS X compiler warning
WT-2347 Java: schema format edge cases
WT-2348 xargs -P isn't portable
WT-2355 Fix minor scratch buffer usage in logging
SERVER-21833 Compact does not release space to the system with WiredTiger
SERVER-21887 $sample takes disproportionately long time on newly created collection
SERVER-22064 Coverity analysis defect 77699: Unchecked return value
SERVER-21944 WiredTiger changes for 3.2.2
Branch: v3.2
https://github.com/mongodb/mongo/commit/5d6532f3d5227ff76f62c4810c98a4ef4d0c8c56