核心数据获取速度非常慢

Question

我正在运行一个非常基本的NSFetchRequest来获取一个实体MessageObject.我只有2000个消息对象,我想要全部检索它们.但是,由于一些奇怪的原因,获取请求超过10秒!

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"MessageObject" inManagedObjectContext:appDelegate.managedObjectContext];
[fetchRequest setEntity:entity];
NSSortDescriptor *sort= [[NSSortDescriptor alloc] initWithKey:@"createDate" ascending:NO selector:@selector(compare:)];
[fetchRequest setSortDescriptors:[NSArray arrayWithObject:sort]];
[fetchRequest setFetchBatchSize:5];

就是这样,那是我的获取请求.我甚至没有使用谓词,它需要超过10秒.对于导致这种情况的原因,我完全不知道.如果有人有任何想法或起点,请分享.

我也尝试过启用SQLite调试logging(-com.apple.CoreData.SQLDebug 1),但是我从这个简单的fetch中获得了数千行输出.这是正常的吗？

 2012-06-22 19:39:59.171 myapp[81825:15e03] about to execute fetch
 2012-06-22 19:39:59.172 myapp[81825:15e03] CoreData: sql: SELECT 0, t0.Z_PK FROM ZMBNOTEOBJECT t0 ORDER BY t0.ZCREATEDATE DESC
 2012-06-22 19:39:59.178 myapp[81825:15e03] CoreData: annotation: sql connection fetch time: 0.0061s
 2012-06-22 19:39:59.179 myapp[81825:15e03] CoreData: annotation: total fetch execution time: 0.0067s for 2052 rows.
 2012-06-22 19:39:59.179 myapp[81825:15e03] CoreData: sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZAUTHOREMAIL, t0.ZAUTHORNAME, t0.ZCREATEDATE, t0.ZISGLOBAL, t0.ZISLOCKED, t0.ZISNEW, t0.ZISPENDINGDELETE, t0.ZISPENDINGLIKE, t0.ZISPENDINGREAD, t0.ZISPENDINGSYNC, t0.ZLASTUPDATED, t0.ZLOCALLYMODIFIEDDATE, t0.ZMAINIDEA, t0.ZMETALASTUPDATED, t0.ZNOTEID, t0.ZNUMBEROFCHILDREN, t0.ZPARENTAUTHOREMAIL, t0.ZPARENTNOTEID, t0.ZROOTAUTHOREMAIL, t0.ZROOTNOTEID, t0.Z4PENDINGADDNOTES, t0.Z4PENDINGREMOVENOTES FROM ZMBNOTEOBJECT t0 WHERE  t0.Z_PK IN  (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)  ORDER BY t0.ZCREATEDATE DESC LIMIT 15
 2012-06-22 19:39:59.180 myapp[81825:15e03] CoreData: annotation: sql connection fetch time: 0.0008s
 2012-06-22 19:39:59.181 myapp[81825:15e03] CoreData: annotation: total fetch execution time: 0.0018s for 15 rows.
 2012-06-22 19:39:59.182 myapp[81825:15e03] CoreData: sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZAUTHOREMAIL, t0.ZAUTHORNAME, t0.ZCREATEDATE, t0.ZISGLOBAL, t0.ZISLOCKED, t0.ZISNEW, t0.ZISPENDINGDELETE, t0.ZISPENDINGLIKE, t0.ZISPENDINGREAD, t0.ZISPENDINGSYNC, t0.ZLASTUPDATED, t0.ZLOCALLYMODIFIEDDATE, t0.ZMAINIDEA, t0.ZMETALASTUPDATED, t0.ZNOTEID, t0.ZNUMBEROFCHILDREN, t0.ZPARENTAUTHOREMAIL, t0.ZPARENTNOTEID, t0.ZROOTAUTHOREMAIL, t0.ZROOTNOTEID, t0.Z4PENDINGADDNOTES, t0.Z4PENDINGREMOVENOTES FROM ZMBNOTEOBJECT t0 WHERE  t0.Z_PK IN  (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)  ORDER BY t0.ZCREATEDATE DESC LIMIT 15
 2012-06-22 19:39:59.186 myapp[81825:15e03] CoreData: annotation: sql connection fetch time: 0.0042s
 2012-06-22 19:39:59.187 myapp[81825:15e03] CoreData: annotation: total fetch execution time: 0.0049s for 15 rows.
 2012-06-22 19:39:59.187 myapp[81825:15e03] CoreData: sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZAUTHOREMAIL, t0.ZAUTHORNAME, t0.ZCREATEDATE, t0.ZISGLOBAL, t0.ZISLOCKED, t0.ZISNEW, t0.ZISPENDINGDELETE, t0.ZISPENDINGLIKE, t0.ZISPENDINGREAD, t0.ZISPENDINGSYNC, t0.ZLASTUPDATED, t0.ZLOCALLYMODIFIEDDATE, t0.ZMAINIDEA, t0.ZMETALASTUPDATED, t0.ZNOTEID, t0.ZNUMBEROFCHILDREN, t0.ZPARENTAUTHOREMAIL, t0.ZPARENTNOTEID, t0.ZROOTAUTHOREMAIL, t0.ZROOTNOTEID, t0.Z4PENDINGADDNOTES, t0.Z4PENDINGREMOVENOTES FROM ZMBNOTEOBJECT t0 WHERE  t0.Z_PK IN  (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)  ORDER BY t0.ZCREATEDATE DESC LIMIT 15
 2012-06-22 19:39:59.188 myapp[81825:15e03] CoreData: annotation: sql connection fetch time: 0.0008s
 2012-06-22 19:39:59.189 myapp[81825:15e03] CoreData: annotation: total fetch execution time: 0.0014s for 15 rows.
... (thousands of more lines similar to above)

我不太熟悉这个,但看起来它在.0067秒内获取了2052行.那么为什么之后会继续做更多的事情呢？如果完成获取行,请求是否应该完成？它是错误的数据还是什么？

此外,我已经删除了setFetchBatchSize - 摆脱了数千行,但获取请求仍然需要很长时间.这是我得到的输出:

2012-06-22 20:07:25.316 myapp[8927:707] about to execute fetch
 2012-06-22 20:07:25.322 myapp[8927:707] CoreData: sql: SELECT 0, t0.Z_PK, t0.Z_OPT, t0.ZAUTHOREMAIL, t0.ZAUTHORNAME, t0.ZCREATEDATE,t0.ZISLOCKED, t0.ZISNEW, t0.ZISPENDINGDELETE, t0.ZISPENDINGSYNC, t0.ZLASTUPDATED, t0.ZLOCALLYMODIFIEDDATE, t0.ZMAINIDEA, t0.ZMETALASTUPDATED, t0.ZNOTEID, t0.ZNUMBEROFCHILDREN, t0.ZPARENTAUTHOREMAIL, t0.ZPARENTNOTEID, t0.ZROOTAUTHOREMAIL, t0.ZROOTNOTEID, t0.Z4PENDINGADDNOTES, t0.Z4PENDINGREMOVENOTES FROM ZMBNOTEOBJECT t0 ORDER BY t0.ZCREATEDATE DESC
 2012-06-22 20:07:26.758 myapp[8927:707] CoreData: annotation: sql connection fetch time: 1.0891s
 2012-06-22 20:07:26.763 myapp[8927:707] CoreData: annotation: total fetch execution time: 1.4407s for 4000 rows.
 2012-06-22 20:07:35.967 myapp[8927:707] finished fetching

奇怪的是,在20:07:26.763它显然说4000行占用了1.4407秒,但是在9秒内没有得到输出说"完成取出"(这是一个NSLog语句出现之后[[self fetchedResultsController] performFetch:&error])是什么了那？

Answer 1

删除 setFetchBatchSize。

如果您的目的是一次加载所有内容，只需将其删除即可。

此外，如果需要加载所有属性，请添加：

fetchRequest.returnsObjectsAsFaults = NO;

它将加载每个实体并填充属性。

您可能只想加载某些属性，因此使用它来选择您需要的属性：

fetchRequest.propertiesToFetch = ...

你就完成了。