Thank you for the quick reply Hick. I've implemented your script file in C
since I'm running this application in the embedded world with no OS. I don't
see a .describe in the SQLite documentation. I've tried to use .schema but
that returns an error. Do you have another suggestion to obtain the table
information you had in mind?
From: Hick Gunter <[email protected]>
To: 'SQLite mailing list' <[email protected]>
Sent: Tuesday, March 20, 2018 9:04 AM
Subject: Re: [sqlite] [EXTERNAL] R*Trees query data cached?
SQLite does not have "query caching". It does have a "page cache" that will
keep heavily used pages iin memory. There is also the possibility of a
file-system/os-level cache. To break down the 1.6 seconds required for the
first query, try executing an sql script. In linux this would be along the
lines of:
> date; sqlite3 file.db < script.sql;date
With script.sql containing:
Select strftime('%Y-%m-%d %H:%M:%S.%f');
Select strftime('%Y-%m-%d %H:%M:%S.%f');
.describe adas_link_geometry
Select strftime('%Y-%m-%d %H:%M:%S.%f');
.describe idx_adas_link_geometry
Select strftime('%Y-%m-%d %H:%M:%S.%f');
Select <your statement>;
Select strftime('%Y-%m-%d %H:%M:%S.%f');
Select <your statement>;
Select strftime('%Y-%m-%d %H:%M:%S.%f');
Select <your statement>;
Select strftime('%Y-%m-%d %H:%M:%S.%f');
This should give you an idea of where the time is being spent.
-----Ursprüngliche Nachricht-----
Von: sqlite-users [mailto:[email protected]] Im
Auftrag von David Ashman - Zone 7 Engineering, LLC
Gesendet: Dienstag, 20. März 2018 16:34
An: [email protected]
Betreff: [EXTERNAL] [sqlite] R*Trees query data cached?
Hello -
I have a question on SQLite query data buffering.
I'm successfully using SQLite v3.22.0 on an embedded ARM processor from ST with
SD card. The database file size is about 750MB. The file system is Segger
emFile FAT32. I've configured SQLite to use 6MB RAM for heap. I've done some
query time benchmarking and found that the very first R*Trees query takes about
1.6 seconds to complete. Each successive R*Trees query (same query string with
slightly different search parameters) takes about 11ms to complete. Being new
to SQLite and spatial queries, I'm trying to understand the substantial query
time differences... does SQLite cache data from each query for future queries?
The initial query:SELECT LINK_ID, FROM_REF_ELEVATION, TO_REF_ELEVATION FROM
adas_link_geometry, idx_adas_link_geometry WHERE adas_link_geometry.ROWID =
idx_adas_link_geometry.id AND minLat > 454760320 AND maxLat < 454800320 AND
minLong > -1226807072 AND maxLong < -1226767072;
Thanks in advance,Dave
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