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Add logic to _bt_set_startikey that determines whether row compare keys are guaranteed to be satisfied by every tuple on a page that is about to be read by _bt_readpage. This works in essentially the same way as the existing scalar inequality logic. Testing has shown that the new logic improves performance to about the same degree as the existing scalar inequality logic (compared to the unoptimized case). In other words, the new logic makes many row compare scans significantly faster. Note that the new row compare inequality logic is only effective when the same individual row member is the deciding subkey for all tuples on the page (obviously, all tuples have to satisfy the row compare, too). This is what makes the new row compare logic very similar to the existing logic for scalar inequalities. Note, in particular, that this makes it safe to ignore whether all row compare members are against either ASC or DESC index attributes (i.e. it doesn't matter if individual subkeys don't all use the same inequality strategy). Also stop refusing to set pstate.startikey to an offset beyond any nonrequired key (don't add logic that'll do that for an individual row compare subkey, either). We can fully rely on our firstchangingattnum tests instead. This will do the right thing when a page has a group of tuples with NULLs in a lower-order attribute that makes the tuples fail to satisfy a row compare key -- we won't incorrectly conclude that all tuples must satisfy the row compare, just because firsttup and lasttup happen to. Our firstchangingattnum test prevents that from happening. (Note that the original "avoid evaluating nbtree scan keys" mechanism added by commit |
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PostgreSQL Database Management System
This directory contains the source code distribution of the PostgreSQL database management system.
PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings.
Copyright and license information can be found in the file COPYRIGHT.
General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/devel/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/devel/installation.html.
The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.