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In an attempt to simplify the tsquery matching engine, the original phrase search patch invented rewrite rules that would rearrange a tsquery so that no AND/OR/NOT operator appeared below a PHRASE operator. But this approach had numerous problems. The rearrangement step was missed by ts_rewrite (and perhaps other places), allowing tsqueries to be created that would cause Assert failures or perhaps crashes at execution, as reported by Andreas Seltenreich. The rewrite rules effectively defined semantics for operators underneath PHRASE that were buggy, or at least unintuitive. And because rewriting was done in tsqueryin() rather than at execution, the rearrangement was user-visible, which is not very desirable --- for example, it might cause unexpected matches or failures to match in ts_rewrite. As a somewhat independent problem, the behavior of nested PHRASE operators was only sane for left-deep trees; queries like "x <-> (y <-> z)" did not behave intuitively at all. To fix, get rid of the rewrite logic altogether, and instead teach the tsquery execution engine to manage AND/OR/NOT below a PHRASE operator by explicitly computing the match location(s) and match widths for these operators. This requires introducing some additional fields into the publicly visible ExecPhraseData struct; but since there's no way for third-party code to pass such a struct to TS_phrase_execute, it shouldn't create an ABI problem as long as we don't move the offsets of the existing fields. Another related problem was that index searches supposed that "!x <-> y" could be lossily approximated as "!x & y", which isn't correct because the latter will reject, say, "x q y" which the query itself accepts. This required some tweaking in TS_execute_ternary along with the main tsquery engine. Back-patch to 9.6 where phrase operators were introduced. While this could be argued to change behavior more than we'd like in a stable branch, we have to do something about the crash hazards and index-vs-seqscan inconsistency, and it doesn't seem desirable to let the unintuitive behaviors induced by the rewriting implementation stand as precedent. Discussion: https://postgr.es/m/28215.1481999808@sss.pgh.pa.us Discussion: https://postgr.es/m/26706.1482087250@sss.pgh.pa.us
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. PostgreSQL has many language interfaces, many of which are listed here: http://www.postgresql.org/download See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.