今天我花了一天时间改进Python脚本的性能,该脚本将数据推送到Postgres数据库中.我之前插入过这样的记录:
query = "INSERT INTO my_table (a,b,c ... ) VALUES (%s, %s, %s ...)";
for d in data:
cursor.execute(query, d)
然后我重新编写了脚本,这样它就创建了一个内存中的文件,而不是Postgres的COPY
命令,该命令允许我将数据从文件复制到表中:
f = StringIO(my_tsv_string)
cursor.copy_expert("COPY my_table FROM STDIN WITH CSV DELIMITER AS E'\t' ENCODING 'utf-8' QUOTE E'\b' NULL ''", f)
COPY
法为staggeringly faster.
METHOD | TIME (secs) | # RECORDS
=======================================
COPY_FROM | 92.998 | 48339
INSERT | 1011.931 | 48377
但我找不到任何关于原因的信息?它的工作原理与多行INSERT
有什么不同,从而使其速度更快?
参见第this benchmark页:
# original
0.008857011795043945: query_builder_insert
0.0029380321502685547: copy_from_insert
# 10 records
0.00867605209350586: query_builder_insert
0.003248929977416992: copy_from_insert
# 10k records
0.041108131408691406: query_builder_insert
0.010066032409667969: copy_from_insert
# 1M records
3.464181900024414: query_builder_insert
0.47070908546447754: copy_from_insert
# 10M records
38.96936798095703: query_builder_insert
5.955034017562866: copy_from_insert