Hi,
Can you tell me why *execute* in .../backends/oracle/base.py sets
*unify_by_values=True* when it calls *_fix_for_params*? It has an
interesting effect on the Oracle cursor cache.
For example, if I use a Django model called Logger like this:
from . import models
...
a = models.Logger(t1="1", t2="2", t3="3", i1=1, i2=2, i3=3)
a.save()
b = models.Logger(t3="3", t2="2", t1="1", i3=3, i2=2, i1=1)
b.save()
c = models.Logger(t1="1", t2="2", t3="3", i1=1,i2=1,i3=3)
c.save()
d = models.Logger(t1="1", t2="2", t3="3", i1=3,i2=1,i3=3)
d.save()
e = models.Logger(t1="1", t2="1", t3="1", i1=1,i2=1,i3=1)
e.save()
It results in the following SQL statements in the Oracle cursor cache:
INSERT INTO "POLLS_LOGGER" ("T1", "T2", "T3", "I1", "I2", "I3") VALUES
(:arg0, :arg1, :arg2, :arg3, :arg4, :arg3) RETURNING "POLLS_LOGGER"."ID"
INTO :arg5
INSERT INTO "POLLS_LOGGER" ("T1", "T2", "T3", "I1", "I2", "I3") VALUES
(:arg0, :arg0, :arg0, :arg1, :arg1, :arg1) RETURNING "POLLS_LOGGER"."ID"
INTO :arg2
INSERT INTO "POLLS_LOGGER" ("T1", "T2", "T3", "I1", "I2", "I3") VALUES
(:arg0, :arg1, :arg2, :arg3, :arg4, :arg5) RETURNING "POLLS_LOGGER"."ID"
INTO :arg6
INSERT INTO "POLLS_LOGGER" ("T1", "T2", "T3", "I1", "I2", "I3") VALUES
(:arg0, :arg1, :arg2, :arg3, :arg3, :arg4) RETURNING "POLLS_LOGGER"."ID"
INTO :arg5
Bind variable names are re-used and shuffled around if any share the same
value. This results in multiple SQL IDs.
If, instead, execute used *unify_by_values=False*, then the Oracle buffer
cache would have a single version of the statement irrespective of bind
values:
INSERT INTO "POLLS_LOGGER" ("T1", "T2", "T3", "I1", "I2", "I3") VALUES
(:arg0, :arg1, :arg2, :arg3, :arg4, :arg5) RETURNING "POLLS_LOGGER"."ID"
INTO :arg6
On the face of it, the use of unify_by_values=False is more efficient (at
least from the database's perspective) because there is only one hard
parse. I guess it doesn't look like a big deal in this example, but I have
seen cases where the cursor cache has (literally) tens of thousands of
repeated cursor cache entries where one would have been used if bind names
were kept consistent and independent of bind value.
Do you think there is a valid case for this default behavior to be changed?
Regards,
Nigel
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