Re: [HACKERS] Re: [COMMITTERS] pgsql: Add --synchronous option to pg_receivexlog, for more reliable WA
On 9/15/15 11:04 PM, Fujii Masao wrote: > If --slot option is specified, pg_receivexlog reports a flush position to > the server even though --synchronous is not specified. So users might think > that --synchrnous option is not necessary for synchronous pg_receivexlog > setting. But that's not true. If --synchronous option is not specified, the > received WAL data is flushed to the disk only when WAL segment is switched. > So the transactions on the master need to wait for a long time, i.e., > we can think that synchronous pg_receivexlog doesn't work smoothly. > To avoid such situation, --synchronous option also needs to be specified and > which makes pg_receivexlog flush WAL data immediately after receiving it. Thank you for this information. I hope to have clarified this in the documentation now. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
[HACKERS] Re: [COMMITTERS] pgsql: Add --synchronous option to pg_receivexlog, for more reliable WA
On Wed, Sep 16, 2015 at 11:25 AM, Peter Eisentraut wrote: > On 11/17/14 12:34 PM, Fujii Masao wrote: >> Add --synchronous option to pg_receivexlog, for more reliable WAL writing. > > The last two sentences of this piece of documentation are a bit > hand-wavy and hard to parse. Could you clarify this? I think that what those sentences try to point is; to make pg_receivexlog run as synchronous standby expectedly, both --slot and --synchronous options need to be specified. If --slot option is specified, pg_receivexlog reports a flush position to the server even though --synchronous is not specified. So users might think that --synchrnous option is not necessary for synchronous pg_receivexlog setting. But that's not true. If --synchronous option is not specified, the received WAL data is flushed to the disk only when WAL segment is switched. So the transactions on the master need to wait for a long time, i.e., we can think that synchronous pg_receivexlog doesn't work smoothly. To avoid such situation, --synchronous option also needs to be specified and which makes pg_receivexlog flush WAL data immediately after receiving it. Regards, -- Fujii Masao -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
[HACKERS] Re: [COMMITTERS] pgsql: Add --synchronous option to pg_receivexlog, for more reliable WA
On 11/17/14 12:34 PM, Fujii Masao wrote: > Add --synchronous option to pg_receivexlog, for more reliable WAL writing. The last two sentences of this piece of documentation are a bit hand-wavy and hard to parse. Could you clarify this? -S slotname --slot=slotname Require pg_receivexlog to use an existing replication slot (see ). When this option is used, pg_receivexlog will report a flush position to the server, indicating when each segment has been synchronized to disk so that the server can remove that segment if it is not otherwise needed. --synchronous option must be specified when making pg_receivexlog run as synchronous standby by using replication slot. Otherwise WAL data cannot be flushed frequently enough for this to work correctly. -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
