On Tue, Feb 21, 2017 at 2:33 PM, Ray Stell <stellr@xxxxxx> wrote:
On 2/21/17 12:26 PM, Keith wrote:
Lost your post somehow, but I see it in the list archive. Thanks, Keith.
On Tue, Feb 21, 2017 at 12:22 PM, Ray Stell <stellr@xxxxxx> wrote:
I'm interested in why I might observed a dramatic difference between pg_xlog files and the archive target files. Other dbs I see have them pretty much one-to-one, but not in this case here. What might cause the large variation? I got only a few pg_xlogs files each minute and 42 archive files/min.On 2/21/17 12:09 AM, Steven Chang wrote:
check this, his 2nd part introduces Stream Replication Implementation and tell you px_log retention and wal archive related parameters.
2017-02-18 2:30 GMT+08:00 Ray Stell <stellr@xxxxxx>:
I was "planning" to turn on WAL archiving on a postgresql 9.4.11 server that currently is running with "wal_level=hot_standby" and streaming to a standby. I thought there would be a relationship between the rate of pg_xlog files and archive generation. When I turned up the archive_command/mode I found the scale of the archive target was wrong as I had based it on the pg_xlog file creation rate.
When I turned on the archive command for a few minutes, pg_xlog dir contained these files for the time period:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 00000001000023AC0000007F
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 00000001000023AC0000007E
The archive command wrote 126, 16MB files:
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000056
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000055
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000054
-rw------- 1 postgres postgres 16777216 Feb 17 06:47 000000010000237700000053
...
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DC
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DB
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000DA
-rw------- 1 postgres postgres 16777216 Feb 17 06:45 0000000100002376000000D9
On servers that are not nearly as busy, I observe a one-to-one relationship between these files/rates.
Is there a good WAL archive space planning guide?
Is the way to collect planning data for this to turn on wal_debug?
TIA!
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Ray,
Did you see my previous response about the archive_timeout setting?
There was a 30 minute timeout set, but I would not think that would increase the archive file generation as observed, does it?
" When this parameter is greater than zero, the server will switch to a new segment file whenever this many seconds have elapsed since the last segment file switch, and there has been any database activity, including a single checkpoint. (Increasing checkpoint_timeout will reduce unnecessary checkpoints on an idle system.) "
Your post seems to indicate having a non-zero value might increase the number of archive files, is that so? Maybe it is in milliseconds which might make sense with the observed archive rate, but the doc says seconds and it was set to 1800. I can set it to 0 and see if it changes things, but I'm a little confused.
If it was set to 30 minutes, then no, it wouldn't explain what you saw. But we didn't know what it was set to, so that's why I asked. Make sure you're checking the value actually set in the database, and not just what's in postgresql.conf, since it could've changed but never been reloaded to put in place (type "show archive_timeout" in psql).
If that's not it, not sure what may be causing what you're seeing.
If that's not it, not sure what may be causing what you're seeing.
Keith
