Why does queryset.iterator() show poor performance
# I am using postgresql
# queryset run complex SQL joining 4 tables
print(queryset.count()) # print 30000
# it takes 5 sec
for i in queryset:
print(i.arg)
# it takes 10 sec
for i in queryset.iterator(chunk_size=30000):
print(i.arg)
I simplify situation I have suffered like above.
iterator() takes more time about 2 times.
Of course, I understand that iterator() need more DB-side operation and more request like DECLARE, FETCH and CLOSE because it is using DB CURSOR internally(in practice I check for Django to emit these request through DB log).
However, I don't think these additional operations will take that much time. It even will fetch all rows at one FETCH request since chunk_size is the same as the total number of rows.
I am wondering if this situation is expected one or not. If it is expected, why it takes that much more time?
python django postgresql-9.5
asked Dec 29 '18 at 15:56
SangminKimSangminKim
2,33442360
add a comment |
# I am using postgresql
# queryset run complex SQL joining 4 tables
print(queryset.count()) # print 30000
# it takes 5 sec
for i in queryset:
print(i.arg)
# it takes 10 sec
for i in queryset.iterator(chunk_size=30000):
print(i.arg)
I simplify situation I have suffered like above.
iterator() takes more time about 2 times.
Of course, I understand that iterator() need more DB-side operation and more request like DECLARE, FETCH and CLOSE because it is using DB CURSOR internally(in practice I check for Django to emit these request through DB log).
However, I don't think these additional operations will take that much time. It even will fetch all rows at one FETCH request since chunk_size is the same as the total number of rows.
I am wondering if this situation is expected one or not. If it is expected, why it takes that much more time?
python django postgresql-9.5
asked Dec 29 '18 at 15:56
SangminKimSangminKim
2,33442360
add a comment |
# I am using postgresql
# queryset run complex SQL joining 4 tables
print(queryset.count()) # print 30000
# it takes 5 sec
for i in queryset:
print(i.arg)
# it takes 10 sec
for i in queryset.iterator(chunk_size=30000):
print(i.arg)
I simplify situation I have suffered like above.
iterator() takes more time about 2 times.
Of course, I understand that iterator() need more DB-side operation and more request like DECLARE, FETCH and CLOSE because it is using DB CURSOR internally(in practice I check for Django to emit these request through DB log).
However, I don't think these additional operations will take that much time. It even will fetch all rows at one FETCH request since chunk_size is the same as the total number of rows.
I am wondering if this situation is expected one or not. If it is expected, why it takes that much more time?
python django postgresql-9.5
asked Dec 29 '18 at 15:56
SangminKimSangminKim
2,33442360
# I am using postgresql
# queryset run complex SQL joining 4 tables
print(queryset.count()) # print 30000
# it takes 5 sec
for i in queryset:
print(i.arg)
# it takes 10 sec
for i in queryset.iterator(chunk_size=30000):
print(i.arg)
I simplify situation I have suffered like above.
iterator() takes more time about 2 times.
Of course, I understand that iterator() need more DB-side operation and more request like DECLARE, FETCH and CLOSE because it is using DB CURSOR internally(in practice I check for Django to emit these request through DB log).
However, I don't think these additional operations will take that much time. It even will fetch all rows at one FETCH request since chunk_size is the same as the total number of rows.
I am wondering if this situation is expected one or not. If it is expected, why it takes that much more time?
python django postgresql-9.5
python django postgresql-9.5
asked Dec 29 '18 at 15:56
SangminKimSangminKim
2,33442360
asked Dec 29 '18 at 15:56
SangminKimSangminKim
2,33442360
asked Dec 29 '18 at 15:56
SangminKimSangminKim
2,33442360
asked Dec 29 '18 at 15:56
SangminKimSangminKim
2,33442360
asked Dec 29 '18 at 15:56
SangminKimSangminKim
2,33442360
2,33442360
add a comment |
add a comment |
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