HI all, While testing the temp file compression patch,noticed that the new temp_file_compression GUC isn't documented yet.I put together a small docs patch to add a short description and clarify that the effect of compression depends on the workload(for example ,hash join spills may not show visible size reduction due to fixed_size chunks).
patch is attached.Happy to adjust the wording if needed. thanks, lakshmi
I tested both patches on current master using git am -3 .They apply cleanly,build fine,and the temp_file _compression GUC works as expected. Query results are unchanged.
For hash join spill test,temp files were created as expected,but the logged size were same for no,lz4,and pglz,which seems consistent with fixed-size fileset chunking.It might be helpful to briefly note this in the documentation to avoid confusion.
Thanks for working on this . best regards, lakshmi
buffile.h:35 and buffile.c:63 - same constants defined first as an Enum and then as #defines - code builds properly without the defines.
buffile.c:121 - compress_tempfile is defined, set to false at :167, but never used otherwise
guc_tables.c:470 - the comment says that pglz isn't supported yet, but we have a value for it, and I see support for it in the code
buffile.c:659: (and at other places) if USE_LZ4 is undefined, the codepath doesn't do anything. I think these ifdefs should follow how other compression code works, such as wal compression where there's an #else path with elog(ERROR, ...) Similarly, maybe there should be an explicit TEMP_NONE_COMPRESSION branch that does nothing, and the default branch should be an error?
buffile.c:265: If seek isn't supported/limited, shouldn't there be at least an assertion about it in BufFileSeek? And tell isn't mentioned, but it seems to me that tell also doesn't work properly.
