[tor-commits] [pyonionoo/master] Find a better hack for OFFSET without LIMIT.

[gsathya at torproject.org]

commit 01893f74ccd519aa45e8a1ebcf7c3cbe3589db8f
Author: Karsten Loesing <karsten.loesing at gmx.net>
Date:   Sun Sep 23 19:58:23 2012 +0200

    Find a better hack for OFFSET without LIMIT.
    
    SQLite doesn't understand OFFSET without LIMIT, which is why the current
    code used a local counter to request TOTAL_ROWS-offset_value as the LIMIT.
    However, that code is not transaction-safe.  A better solution is to pass
    -1 as the LIMIT, which has the same effect.
---
 pyonionoo/database.py |   12 ++----------
 1 files changed, 2 insertions(+), 10 deletions(-)

diff --git a/pyonionoo/database.py b/pyonionoo/database.py
index a7d909b..a553629 100644
--- a/pyonionoo/database.py
+++ b/pyonionoo/database.py
@@ -30,12 +30,6 @@ DB_UPDATE_INTERVAL = 60
 # The timer object used for updating the database.
 FRESHEN_TIMER = None
 
-# Total number of rows in summary db. This can also be calculated during
-# run time by doing "SELECT COUNT(*) FROM summary" but this will take
-# time to execute. It seems like a better idea to count the number of rows
-# during insertion.
-TOTAL_ROWS = 0
-
 # Database schemas.
 # Summary database:  in conjunction with addresses and flags, holds the
 # information in the summary document.  addresses and flags are lists of
@@ -122,7 +116,7 @@ def update_databases(summary_file=None):
     @type summary_file: string
     @param summary_file: full path to the summary file
     """
-    global DB_CREATION_TIME, TABLE_ROWS
+    global DB_CREATION_TIME
 
     if DB_CREATION_TIME >= os.stat(summary_file).st_mtime:
         return
@@ -137,7 +131,6 @@ def update_databases(summary_file=None):
     logging.info("Deleting data from databases")
     CURSOR = conn.cursor()
     CURSOR.execute('DELETE FROM %s' % summary_tbl_name)
-    TABLE_ROWS = 0
 
     # Create the summary database.  We could accumulate all the router tuples
     # and then insert them with an executemany(...) in one go, except that
@@ -176,7 +169,6 @@ def update_databases(summary_file=None):
             # or might allow users to optimize in this way.
             CURSOR.execute(summary_insert_stmt, router_tuple)
             id_num = CURSOR.lastrowid
-            TABLE_ROWS += 1
 
     conn.commit()
     logging.info("Table updated")
@@ -228,7 +220,7 @@ def query_summary_tbl(running_filter=None, type_filter=None, hex_fingerprint_fil
         if not limit_value:
             # sqlite doesn't support OFFSET without a LIMIT clause, this is
             # a hack to get around that.
-            limit_clause = 'LIMIT %s' % (TOTAL_ROWS-int(offset_value))
+            limit_clause = 'LIMIT -1'
         offset_clause = 'OFFSET %s' % offset_value
     cursor.execute('SELECT %s FROM summary %s %s %s %s' %
                    (','.join(fields), where_clause, order_clause, limit_clause,