SUMMARY

SYNTAX

ROLLBACK
COMMIT
RECALLTRACE (or simply RECALL)

DESCRIPTION

Context: In order to support multiple data formats with as little information loss as possible, SAC's internal data storage has been augmented with I/O buffers based on the CSS 3.0 schema. Computations continue to be performed on the data stored in the original SAC-format headers, but most I/O takes place using the data stored in the I/O buffers. Because there are two copies of the data in memory, and because most SAC commands do not affect the copy stored in the I/O buffers, SAC can revert to the copy in the I/O buffer to effectively erase unwanted changes without having to re-read the data.

ROLLBACK

After a series of operations on the data you can issue the ROLLBACK command, and the operations will be undone; the datafiles in SAC's internal data storage are replaced with the corresponding files in the I/O buffer, which represent the last committed version of the data files.

COMMIT

After a series of operations on the data you can issue the COMMIT command, any changes to the header values and the waveforms will be copied from the SAC headers to the I/O buffers. Future ROLLBACK commands will revert to this committed data.

RECALLTRACE

The RECALLTRACE command:

• rolls back the waveforms
• rolls back those header variables which are tightly linked to the waveforms
• commits those variables which are loosely linked to the waveforms.

This allows the user the flexibility to read a file, filter it, process it, and change some of the header variables not tightly linked to the waveform (make picks, establish new event location, etc.) and then recall the original waveform while saving the new header values. The user need not worry about ending up with header variables which are inconsistent with the waveform, because RECALLTRACE will roll those variables back with the waveform.

The following header variables are considered tightly linked to the waveform:

DELTA ODELTA  DEPMIN  DEPMAX  DEPMEN  STLA  STLO  STEL  STDP
CMPAZ CMPINC  XMINIMUM  XMAXIMUM  YMINIMUM  YMAXIMUM
NPTS  NXSIZE  NYSIZE  NVHDR NORID NEVID NWFID
IFTYPE  IDEP  IINST ISTREG  IZTYPE  ISYNTH  LEVEN LPSPOL
KSTNM KINST KCMPNM  KHOLE KNETWK

The following header variables are considered loosely linked to the waveform::

B E O A T0 T1 T2 T3 T4 T5 T6 T7 T8 T9 F EVLA EVLO EVEL EVDP MAG USER0 USER1 USER2 USER3 USER4 USER5 USER6 USER7 USER8 USER9 DIST AZ BAZ GCARC RESP0 RESP1 RESP2 RESP3 RESP4 RESP5 RESP6 RESP7 RESP8 RESP9 NZYEAR NZJDAY NZHOUR NZMIN NZSEC NZMSEC IEVTYP IMAGTYP IMAGSRC IEVREG IQUAL LOVROK LCALDA KDATRD KEVNM KO KA KT0 KT1 KT2 KT3 KT4 KT5 KT6 KT7 KT8 KT9 KF KUSER0 KUSER1 KUSER2

EXAMPLES

The COMMIT command is used on the 14th line of the following example. Run the example three times: the second time use ROLLBACK in place of COMMIT. The third time, use RECALLTRACE:

SAC> FG SEIS
SAC> RTR
SAC> P1
SAC> LH KSTNM KEVNM
SAC> CH KSTNM KAH KEVNM SOMEEVENT
SAC> ENVELOPE
SAC> PPK
SAC> user picks T1 at the change in frequency content
SAC> P1
SAC> LH KSTNM KEVNM
SAC> COMMIT       # replace with ROLLBACK or RECALLTRACE as appropriate
SAC> P1
SAC> LH KSTNM KEVNM

RESULTS

When running this example with the COMMIT command, the final P1 will display the enveloped data and the T1 pick; the LH will display the new values for KSTNM and KEVNM which were set with the CH command.

When running this example with the ROLLBACK command, the final P1 will display the unprocessed file produced by the FG command and the T1 pick will be lost; the LH will display the original values of KSTNM and KEVNM.

When running this example with the RECALLTRACE command, the final P1 will display the unprocessed file produced by the FG command but the T1 pick will be preserved; the LH will display the original value of KSTNM and the new value of KEVNM.

SEE COMMANDS

DATAGEN, DELETECHANNEL, DELETESTACK, MERGE, READ, READALPHA, READCSS, READGSE, READHDR, READSDD, READSUDS, SORT, WRITE, WRITECSS, WRITEHDR, WRITESP, WRITESTACK

WARNING

Certain SAC commands will automatically commit your data for you. Because there are now two data storage locations, certain SAC commands will require that the two sets of files be made consitent with each other prior to executing the command. The following commands require consistency every time they are called:

MERGE SORT WRITE WRITECSS WRITEHDR WRITESP WRITESTACK

The following commands require consistency when the MORE option is specified:

DATAGEN READ READTABLE READCSS READGSE READHDR READSDD READSUDS

These commands will by default commit the data before executing. Each of these commands takes options to allow it to rollback or recall the data prior to execution. The options are COMMIT, ROLLBACK, and RECALLTRACE. COMMIT is the default.

Changing the option in any one of these commands changes it in all of them for future calls.

Note: Because there are now two data storage locations, we optimized flexibility of the DELETECHANNEL and DELETESTACK commands by allowing the COMMIT option to control whether the datafiles are deleted from the I/O buffers. When either of these delete commands are used with COMMIT ON, the specified data files are deleted from the I/O buffers as well as the SAC internal data storage; subsequent ROLLBACK commands will find no trace of the deleted files. When one of these delete commands is issued with COMMIT OFF, the specified datafiles are deleted from the SAC internal data storage, but not from the I/O buffers; subsequent calls to ROLLBACK will return these files to the SAC internal data storage. There is an exception: when DELETECHANNEL is called with the ALL option, all datafiles will be deleted from SAC internal storage and the I/O buffers regardless of the COMMIT option. The default is COMMIT OFF. See DELETECHANNEL and DELETESTACK for details.

Changing the COMMIT option in one delete command changes it in both for future calls. The COMMIT option for DELETECHANNEL and DELETESTACK is unrelated to the COMMIT option in other commands listed in the Warning above.

LATEST REVISION

October 29, 1998 (Version 00.58beta)