Hello Nigel, Through git blame for unify_by_values I figured it was introduced[0] to deal with an issue during aggregation[1].
Mariusz might be able to provide more context here as I don't have much knowledge around Oracle cursor cache but it seems you'll have to find another way to address the aggregation issue[1] if you'd like to change this behaviour. Cheers, Simon [0] https://github.com/django/django/commit/6dbe56ed7855f34585884a2381fb1cec22ddc824 [1] https://code.djangoproject.com/ticket/27632 Le samedi 3 avril 2021 à 18:30:28 UTC-4, NPB a écrit : > 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 > -- You received this message because you are subscribed to the Google Groups "Django developers (Contributions to Django itself)" group. To unsubscribe from this group and stop receiving emails from it, send an email to django-developers+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/django-developers/9d334ded-b171-4053-ad71-14d3eac5b3cen%40googlegroups.com.
