[sqlite] FW: Direct access of table data
From: Nathan Biggs [mailto:nbi...@mycfs.com]
Sent: Wednesday, April 21, 2010 2:43 PM
To: Griggs, Donald
Subject: Re: [sqlite] Direct access of table data
Griggs,
Thanks for the quick reply. I guess I'm just getting greedy since sqlite is so
much faster than our standard databases ("progress").
When you run a query for select * from table, does it literally copy the
contents of the table, or does it just build a structure that points to the
data in the table?
On 4/21/2010 2:29 PM, Griggs, Donald wrote:
Hello Biggs, this is Griggs,
Re: "Is there a way to read the values of a table directly without building and
executing a query. I have a function that has predefined memory..."
No easy way. The sophistication of database abstraction is the reason you
presumably chose to use sqlite.
Re: "I thought it might perform much [better] without all .."
If you've measured this and the query truly takes too long, you might try
(in order):
1) trying to optimize the query (do you have ideal indexing, for instance?)
2) restructure your data/program
3) use a simple file rather than a database
Regards,
Donald Griggs
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Re: [sqlite] FW: Direct access of table data
Briggs,
Re: "I guess I'm just getting greedy since sqlite is so much faster than our
standard databases ("progress")."
That's a distinct possibility.;-)
Re: "When you run a query for select * from table, does it literally copy the
contents of the table, or does it just build a structure that points to the
data in the table?"
When you wrote "points to the data in the table" -- by "table" do you mean
the data on your disk drive? If so, then yes, sqlite must read the data into
RAM, and at least one ram-to-ram copy is implied. (The data for a row might
span multiple db pages.) If you're using an sqlite wrapper, that may possibly
perform a copy as well.
If you're using multi-megabyte BLOB's then these can be an exception, as
you may read them incrementally:
http://www.sqlite.org/c3ref/blob_read.html
If, however, you're NOT using large blobs, then considerations such as your
synchronization level,
http://www.sqlite.org/pragma.html#pragma_synchronous
indexing, page size, etc. are usually much more important to performance than
a ram-to-ram copy.
Again, have you measured the time to perform the query in question? Is it
worrisome? If not, don't worry.
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