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Both of these modules dumped each bit of output that they got from the underlying compression library as a separate "data block" in the emitted archive file. In the case of zstd this'd frequently result in block sizes well under 100 bytes; lz4 is a little better but still produces blocks around 300 bytes, at least in the test case I tried. This bloats the archive file a little bit compared to larger block sizes, but the real problem is that when pg_restore has to skip each data block rather than seeking directly to some target data, tiny block sizes are enormously inefficient. Fix both modules so that they fill their allocated buffer reasonably well before dumping a data block. In the case of lz4, also delete some redundant logic that caused the lz4 frame header to be emitted as a separate data block. (That saves little, but I see no reason to expend extra code to get worse results.) I fixed the "stream API" code too. In those cases, feeding small amounts of data to fwrite() probably doesn't have any meaningful performance consequences. But it seems like a bad idea to leave the two sets of code doing the same thing in two different ways. In passing, remove unnecessary "extra paranoia" check in _ZstdWriteCommon. _CustomWriteFunc (the only possible referent of cs->writeF) already protects itself against zero-length writes, and it's really a modularity violation for _ZstdWriteCommon to know that the custom format disallows empty data blocks. Also, fix Zstd_read_internal to do less work when passed size == 0. Reported-by: Dimitrios Apostolou <jimis@gmx.net> Author: Tom Lane <tgl@sss.pgh.pa.us> Reviewed-by: Chao Li <li.evan.chao@gmail.com> Discussion: https://postgr.es/m/3515357.1760128017@sss.pgh.pa.us |
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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/.