Re: PATCH: logical_work_mem and logical streaming of largein-progress transactions

On Fri, 29 May 2020 at 15:52, Amit Kapila <amit.kapila16@gmail.com> wrote:
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To see all the operations(DDL's and DML's), please see test_results

Testing summary:

Basically, we are writing per command invalidation message and for testing that I have tested with different combinations of the DDL and DML operation.  I have not observed any performance degradation with the patch. For "create index" DDL's, %change in wal is 1-7% for 1-15 DDL's. For "add col int/date" DDL's, it is 11-17% for 1-15 DDL's and for "add col text" DDL's, it is 2-6% for 1-15 DDL's. For mix (DDL & DML), it is 2-10%.

why are we seeing 11-13 % of the extra wall, basically,  the amount of extra WAL is not very high but the amount of WAL generated with add column int/date is just ~1000 bytes so additional 100 bytes will be around 10% and for add column text it is  ~35000 bytes so % is less. For text, these ~35000 bytes are due to toast

There is no change in wal size for DML operations. For savepoints, we are getting max 8 bytes per savepoint wal increment (basically for Sub-transaction, we are adding 5 bytes to store xid but due to padding, it is 8 bytes and some times if wal is already aligned, then we are getting 0 bytes increment)