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6cff5a3e08
This commit makes psycopg2 responsible for sending the status update (feedback) messages to the server regardless of whether a synchronous or asynchronous connection is used. Feedback is sent every *status_update* (default value is 10) seconds, which could be configured by passing a corresponding parameter to the `start_replication()` or `start_replication_expert()` methods. The actual feedback message is sent by the `pq_read_replication_message()` when the *status_update* timeout is reached. The default behavior of the `send_feedback()` method is changed. It doesn't send a feedback message on every call anymore but just updates internal structures. There is still a way to *force* sending a message if *force* or *reply* parameters are set. The new approach has certain advantages: 1. The client can simply call the `send_feedback()` for every processed message and the library will take care of not overwhelming the server. Actually, in the synchronous mode it is even mandatory to confirm every processed message. 2. The library tracks internally the pointer of the last received message which is not keepalive. If the client confirmed the last message and after that server sends only keepalives with increasing *wal_end*, the library can safely move forward *flush* position to the *wal_end* and later automatically report it to the server. Reporting of the *wal_end* received from keepalive messages is very important. Not doing so casing: 1. Excessive disk usage, because the replication slot prevents from WAL being cleaned up. 2. The smart and fast shutdown of the server could last indefinitely because walsender waits until the client report *flush* position equal to the *wal_end*. This implementation is only extending the existing API and therefore should not break any of the existing code.
65 lines
2.3 KiB
C
65 lines
2.3 KiB
C
/* replication_cursor.h - definition for the psycopg replication cursor type
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*
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* Copyright (C) 2015-2019 Daniele Varrazzo <daniele.varrazzo@gmail.com>
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*
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* This file is part of psycopg.
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*
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* psycopg2 is free software: you can redistribute it and/or modify it
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* under the terms of the GNU Lesser General Public License as published
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* by the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* In addition, as a special exception, the copyright holders give
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* permission to link this program with the OpenSSL library (or with
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* modified versions of OpenSSL that use the same license as OpenSSL),
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* and distribute linked combinations including the two.
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*
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* You must obey the GNU Lesser General Public License in all respects for
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* all of the code used other than OpenSSL.
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*
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* psycopg2 is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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* License for more details.
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*/
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#ifndef PSYCOPG_REPLICATION_CURSOR_H
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#define PSYCOPG_REPLICATION_CURSOR_H 1
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#include "psycopg/cursor.h"
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#include "libpq_support.h"
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#ifdef __cplusplus
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extern "C" {
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#endif
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extern HIDDEN PyTypeObject replicationCursorType;
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typedef struct replicationCursorObject {
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cursorObject cur;
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int consuming:1; /* if running the consume loop */
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int decode:1; /* if we should use character decoding on the messages */
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struct timeval last_io; /* timestamp of the last exchange with the server */
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struct timeval status_interval; /* time between status packets sent to the server */
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XLogRecPtr write_lsn; /* LSNs for replication feedback messages */
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XLogRecPtr flush_lsn;
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XLogRecPtr apply_lsn;
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XLogRecPtr wal_end; /* WAL end pointer from the last exchange with the server */
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XLogRecPtr last_msg_data_start; /* WAL pointer to the last non-keepalive message from the server */
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struct timeval last_feedback; /* timestamp of the last feedback message to the server */
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} replicationCursorObject;
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RAISES_NEG HIDDEN int repl_curs_datetime_init(void);
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#ifdef __cplusplus
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}
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#endif
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#endif /* !defined(PSYCOPG_REPLICATION_CURSOR_H) */
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