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Add brief documentation to explain how the database export maintains backward and forward compatibility. Signed-off-by: Adrian Hunter <adrian.hunter@intel.com> Cc: Jiri Olsa <jolsa@redhat.com> Link: http://lkml.kernel.org/r/20190520113728.14389-15-adrian.hunter@intel.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
42 lines
1.6 KiB
Plaintext
42 lines
1.6 KiB
Plaintext
Database Export
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===============
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perf tool's python scripting engine:
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tools/perf/util/scripting-engines/trace-event-python.c
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supports scripts:
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tools/perf/scripts/python/export-to-sqlite.py
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tools/perf/scripts/python/export-to-postgresql.py
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which export data to a SQLite3 or PostgreSQL database.
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The export process provides records with unique sequential ids which allows the
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data to be imported directly to a database and provides the relationships
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between tables.
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Over time it is possible to continue to expand the export while maintaining
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backward and forward compatibility, by following some simple rules:
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1. Because of the nature of SQL, existing tables and columns can continue to be
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used so long as the names and meanings (and to some extent data types) remain
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the same.
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2. New tables and columns can be added, without affecting existing SQL queries,
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so long as the new names are unique.
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3. Scripts that use a database (e.g. exported-sql-viewer.py) can maintain
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backward compatibility by testing for the presence of new tables and columns
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before using them. e.g. function IsSelectable() in exported-sql-viewer.py
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4. The export scripts themselves maintain forward compatibility (i.e. an existing
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script will continue to work with new versions of perf) by accepting a variable
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number of arguments (e.g. def call_return_table(*x)) i.e. perf can pass more
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arguments which old scripts will ignore.
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5. The scripting engine tests for the existence of script handler functions
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before calling them. The scripting engine can also test for the support of new
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or optional features by checking for the existence and value of script global
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variables.
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