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The various variants of jsonb_agg() operate as follows, for each aggregate input value: 1. Build a JsonbValue tree representation of the input value. 2. Flatten the JsonbValue tree into a Jsonb in on-disk format. 3. Iterate through the Jsonb, building a JsonbValue that is part of the aggregate's state stored in aggcontext, but is otherwise identical to what phase 1 built. This is very slightly less silly than it sounds, because phase 1 involves calling non-JSONB code such as datatype output functions, which are likely to leak memory, and we don't want to leak into the aggcontext. Nonetheless, phases 2 and 3 are accomplishing exactly nothing that is useful if we can make phase 1 put the JsonbValue tree where we need it. We could probably do that with a bunch of MemoryContextSwitchTo's, but what seems more robust is to give pushJsonbValue the responsibility of building the JsonbValue tree in a specified non-current memory context. The previous patch created the infrastructure for that, and this patch simply makes the aggregate functions use it and then rips out phases 2 and 3. For me, this makes jsonb_agg() with a text column as input run about 2X faster than before. It's not yet on par with json_agg(), but this removes a whole lot of the difference. Author: Tom Lane <tgl@sss.pgh.pa.us> Reviewed-by: jian he <jian.universality@gmail.com> Reviewed-by: Chao Li <li.evan.chao@gmail.com> Discussion: https://postgr.es/m/1060917.1753202222@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.
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/.