| 1 | How And Why To Use TDB Tracing
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| 2 | ==============================
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| 3 |
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| 4 | You can trace all TDB operations, using TDB_TRACE. It is not complete
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| 5 | (error conditions which expect to the logged will not always be traced
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| 6 | correctly, so you should set up a logging function too), but is designed
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| 7 | to collect benchmark-style traces to allow us to optimize TDB.
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| 8 |
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| 9 | Note: tracing is not efficient, and the trace files are huge: a
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| 10 | traverse of the database is particularly large! But they compress very
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| 11 | well with rzip (http://rzip.samba.org)
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| 12 |
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| 13 | How to gather trace files:
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| 14 | --------------------------
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| 15 | 1) Uncomment /* #define TDB_TRACE 1 */ in tdb_private.h.
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| 16 | 2) Rebuild TDB, and everything that uses it.
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| 17 | 3) Run something.
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| 18 |
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| 19 | Your trace files will be called <tdbname>.trace.<pid>. These files
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| 20 | will not be overwritten: if the same process reopens the same TDB, an
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| 21 | error will be logged and tracing will be disabled.
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| 22 |
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| 23 | How to replay trace files:
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| 24 | --------------------------
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| 25 | 1) For benchmarking, remember to rebuild tdb with #define TDB_TRACE commented
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| 26 | out again!
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| 27 | 2) Grab the latest "replace_trace.c" from CCAN's tdb module (tools/ dir):
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| 28 | http://ccan.ozlabs.org/tarballs/tdb.tar.bz2
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| 29 | 3) Compile up replay_trace, munging as necessary.
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| 30 | 4) Run replay_trace <scratch-tdb-name> <tracefiles>...
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| 31 |
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| 32 | If given more than one trace file (presumably from the same tdb)
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| 33 | replay_trace will try to figure out the dependencies between the operations
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| 34 | and fire off a child to run each trace. Occasionally it gets stuck, in
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| 35 | which case it will add another dependency and retry. Eventually it will
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| 36 | give a speed value.
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| 37 |
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| 38 | replay_trace can intuit the existence of previous data in the tdb (ie.
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| 39 | activity prior to the trace(s) supplied) and will prepopulate as
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| 40 | neccessary.
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| 41 |
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| 42 | You can run --quiet for straight benchmark results, and -n to run multiple
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| 43 | times (this saves time, since it need only calculate dependencies once).
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| 44 |
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| 45 | Good luck!
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| 46 | Rusty Russell <rusty@rustcorp.com.au>
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