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Overview
Comment:Clarification that the overwrite optimization does not affect the behavior of triggers.
Timelines: family | ancestors | descendants | both | branch-3.24
Files: files | file ages | folders
SHA3-256:27b8057665f267768844b5e6634b41989946c8792b63fad0181821d812e5c705
User & Date: drh 2018-06-05 23:20:09
Context
2018-06-09
22:13
Fix typos in the compile.html page. check-in: 10c05df9fb user: drh tags: branch-3.24
2018-06-08
13:21
Use https for all internal hyperlinks. Leaf check-in: 59e5f9e3da user: drh tags: branch-3.24-https
2018-06-05
23:20
Clarification that the overwrite optimization does not affect the behavior of triggers. check-in: 27b8057665 user: drh tags: branch-3.24
2018-06-04
19:41
Add the upsert-clause.gif image. check-in: 7d927bcea1 user: drh tags: trunk
Changes
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Changes to pages/changes.in.

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<li> Automatically intercepts the raw [EXPLAIN QUERY PLAN] 
     output and reformats it into an ASCII-art graph.
<li> Lines that begin with "#" and that are not in the middle of an
     SQL statement are interpreted as comments.
<li> Added the --append option to the ".backup" command.
<li> Added the ".dbconfig" command.
<p><b>Performance:</b>
<li> [UPDATE] avoids writing database pages that do not actually change.

     For example, "UPDATE t1 SET x=25 WHERE y=?" becomes a no-op if the
     value in column x is already 25.  Similarly, 
     when doing [UPDATE] on records that span multiple pages, only write
     the subset of pages that contain the changed value(s).



<li> Queries that use ORDER BY and LIMIT now try to avoid computing
     rows that cannot possibly come in under the LIMIT. This can greatly
     improve performance of ORDER BY LIMIT queries, especially when the
     LIMIT is small relative to the number of unrestricted output rows.
<li> The [OR optimization] is allowed to proceed
     even if the OR expression has also been converted into an IN
     expression.  Uses of the OR optimization are now also 







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<li> Automatically intercepts the raw [EXPLAIN QUERY PLAN] 
     output and reformats it into an ASCII-art graph.
<li> Lines that begin with "#" and that are not in the middle of an
     SQL statement are interpreted as comments.
<li> Added the --append option to the ".backup" command.
<li> Added the ".dbconfig" command.
<p><b>Performance:</b>
<li> [UPDATE] avoids unnecessary low-level disk writes when the contents
     of the database file do not actually change.
     For example, "UPDATE t1 SET x=25 WHERE y=?" generates no extra 
     disk I/O if the value in column x is already 25.  Similarly, 
     when doing [UPDATE] on records that span multiple pages, only
     the subset of pages that actually change are written to disk.
     This is a low-level performance optimization only and does not
     affect the behavior of TRIGGERs or other higher level SQL
     structures.
<li> Queries that use ORDER BY and LIMIT now try to avoid computing
     rows that cannot possibly come in under the LIMIT. This can greatly
     improve performance of ORDER BY LIMIT queries, especially when the
     LIMIT is small relative to the number of unrestricted output rows.
<li> The [OR optimization] is allowed to proceed
     even if the OR expression has also been converted into an IN
     expression.  Uses of the OR optimization are now also