File: checkpoint-c.text

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Checkpointing:

    With very large databases there is a significant probability of a system crash
during any one classification try.  Under such circumstances it is advisable to
take the time to checkpoint the calculations for possible restart.

    Checkpointing is initiated by specifying the CHECKPOINT_P keyword parameter
value as true in the ".s-params" file.  This causes the inner convergence step, 
to save a copy of the classification onto the checkpoint file each time the
classification is updated, providing a certain period of time has elapsed.
The file extension is ".chkpt[-bin]".

    Each time a AutoClass completes a cycle, a "." is output to the screen to
provide you with information to be used in setting the MIN_CHECKPOINT_PERIOD
value (default 10800 seconds or 3 hours).  There is obviously a trade-off 
between frequency of checkpointing and the probability that your machine may 
crash, since the repetitive writing of the checkpoint file will slow the 
search process.


Restarting AutoClass Search:

    To recover the classification and continue the search after rebooting and
reloading AutoClass, specify RECONVERGE_TYPE = "chkpt" in the ".s-params" file
(specify FORCE_NEW_SEARCH_P as false).

AutoClass will reload the appropriate database and models, provided there has
been no change in their filenames since the time they were loaded for the
checkpointed classification run.  The ".s-params" file contains any non-
default arguments that were provided to the original call.

In the beginning of a search, before START_J_LIST has been emptied, it will be
necessary to trim the original list to what would have remained in the crashed
search.  This can be determined by looking at the ".log" file to determine what
values were already used.  If the START_J_LIST has been emptied, then an empty
START_J_LIST should be specified in the ".s-params" file.  This is done either
by
        start_j_list =
or
        start_j_list = -9999 

Here is an a set of scripts to demonstrate check-pointing:

% autoclass -search data/glass/glassc.db2 data/glass/glass-3c.hd2 \
                data/glass/glass-mnc.model data/glass/glassc-chkpt.s-params
Run 1)
## glassc-chkpt.s-params
max_n_tries = 2
force_new_search_p = true
## --------------------
;; run to completion

Run 2)
## glassc-chkpt.s-params
force_new_search_p = false
max_n_tries = 10
checkpoint_p = true
min_checkpoint_period = 2
## --------------------
;; after 1 checkpoint, ctrl-C to simulate cpu crash

Run 3)
## glassc-chkpt.s-params
force_new_search_p = false
max_n_tries = 1
checkpoint_p = true
min_checkpoint_period = 1
reconverge_type = "chkpt"
## --------------------
;; checkpointed trial should finish 

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