[PATCH] perf script: turn AUTOCOMMIT off for bulk SQL inserts in event_analyzing_sample.py

[Emmet Caulfield]

The example script tools/perf/scripts/python/event_analyzing_sample.py
contains a minor error. This script takes a perf.data file and
populates a SQLite database with it.

There's a long comment on lines 29-34 to the effect that it takes a
long time to populate the database if the .db file is on disk, so it's
done in the "ramdisk" (/dev/shm/perf.db), but the problem here is
actually line 36:

    con.isolation_level=None

This line turns on AUTOCOMMIT, making every INSERT statement into its
own transaction, and greatly slowing down a bulk insert (25 minutes
vs. a few seconds to insert 15,000 records). This is best solved by
merely omitting this line or changing it to:

    con.isolation_level='DEFERRED'

After making this change, if the database is in memory, it takes
roughly 0.5 seconds to insert 15,000 records and 0.8 seconds if the
database file is on disk, effectively solving the problem.

Given that the whole purpose of having AUTOCOMMIT turned on is to
ensure that individual insert/update/delete operations are committed
to persistent storage, moving the .db file to a ramdisk defeats the
purpose of turning this option on in the first place. Thus
leaving/turning it *off* with the file on disk is no worse. It is
pretty much standard practice to defer transactions and index updates
for bulk inserts like this anyway.

The following patch deletes the offending line and updates the
associated comment.

Emmet.


--- tools/perf/scripts/python/event_analyzing_sample.py~
2013-06-03 15:38:41.762331865 -0700
+++ tools/perf/scripts/python/event_analyzing_sample.py 2013-06-03
15:43:48.978344602 -0700
@@ -26,14 +26,9 @@
 from perf_trace_context import *
 from EventClass import *

-#
-# If the perf.data has a big number of samples, then the insert operation
-# will be very time consuming (about 10+ minutes for 10000 samples) if the
-# .db database is on disk. Move the .db file to RAM based FS to speedup
-# the handling, which will cut the time down to several seconds.
-#
+# Create/connect to a SQLite3 database:
 con = sqlite3.connect("/dev/shm/perf.db")
-con.isolation_level = None
+

 def trace_begin():
        print "In trace_begin:\n"
--
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