On Thu, Jun 6, 2024 at 6:22 PM Julien Tachoires <jul...@gmail.com> wrote: > > Le jeu. 6 juin 2024 à 04:13, Amit Kapila <amit.kapil...@gmail.com> a écrit : > > > > On Thu, Jun 6, 2024 at 4:28 PM Julien Tachoires <jul...@gmail.com> wrote: > > > > > > When the content of a large transaction (size exceeding > > > logical_decoding_work_mem) and its sub-transactions has to be > > > reordered during logical decoding, then, all the changes are written > > > on disk in temporary files located in pg_replslot/<slot_name>. > > > Decoding very large transactions by multiple replication slots can > > > lead to disk space saturation and high I/O utilization. > > > > > > > Why can't one use 'streaming' option to send changes to the client > > once it reaches the configured limit of 'logical_decoding_work_mem'? > > That's right, setting subscription's option 'streaming' to 'on' moves > the problem away from the publisher to the subscribers. This patch > tries to improve the default situation when 'streaming' is set to > 'off'. >
Can we think of changing the default to 'parallel'? BTW, it would be better to use 'parallel' for the 'streaming' option, if the workload has large transactions. Is there a reason to use a default value in this case? > > > 2. Do we want a GUC to switch compression on/off? > > > > > > > It depends on the overhead of decoding. Did you try to measure the > > decoding overhead of decompression when reading compressed files? > > Quick benchmarking executed on my laptop shows 1% overhead. > Thanks. We probably need different types of data (say random data in bytea column, etc.) for this. -- With Regards, Amit Kapila.
