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Rework XLogReader callback system

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Code review for 0dc8ead463, prompted by a bug closed by 91c40548d5.

XLogReader's system for opening and closing segments had gotten too
complicated, with callbacks being passed at both the XLogReaderAllocate
level (read_page) as well as at the WALRead level (segment_open).  This
was confusing and hard to follow, so restructure things so that these
callbacks are passed together at XLogReaderAllocate time, and add
another callback to the set (segment_close) to make it a coherent whole.
Also, ensure XLogReaderState is an argument to all the callbacks, so
that they can grab at the ->private data if necessary.

Document the whole arrangement more clearly.

Author: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Discussion: https://postgr.es/m/20200422175754.GA19858@alvherre.pgsql
This commit is contained in:
Alvaro Herrera
2020-05-08 15:30:34 -04:00
parent 871696ba20
commit b060dbe000
13 changed files with 214 additions and 113 deletions
Download Patch File Download Diff File Expand all files Collapse all files

20
src/backend/replication/logical/logical.c
View File

@ -120,7 +120,7 @@ StartupDecodingContext(List *output_plugin_options,
TransactionId xmin_horizon,
bool need_full_snapshot,
bool fast_forward,
XLogPageReadCB read_page,
XLogReaderRoutine *xl_routine,
LogicalOutputPluginWriterPrepareWrite prepare_write,
LogicalOutputPluginWriterWrite do_write,
LogicalOutputPluginWriterUpdateProgress update_progress)
@ -169,7 +169,7 @@ StartupDecodingContext(List *output_plugin_options,
ctx->slot = slot;
ctx->reader = XLogReaderAllocate(wal_segment_size, NULL, read_page, ctx);
ctx->reader = XLogReaderAllocate(wal_segment_size, NULL, xl_routine, ctx);
if (!ctx->reader)
ereport(ERROR,
(errcode(ERRCODE_OUT_OF_MEMORY),
@ -215,7 +215,8 @@ StartupDecodingContext(List *output_plugin_options,
* Otherwise, we set for decoding to start from the given LSN without
* marking WAL reserved beforehand. In that scenario, it's up to the
* caller to guarantee that WAL remains available.
* read_page, prepare_write, do_write, update_progress --
* xl_routine -- XLogReaderRoutine for underlying XLogReader
* prepare_write, do_write, update_progress --
* callbacks that perform the use-case dependent, actual, work.
*
* Needs to be called while in a memory context that's at least as long lived
@ -230,7 +231,7 @@ CreateInitDecodingContext(char *plugin,
List *output_plugin_options,
bool need_full_snapshot,
XLogRecPtr restart_lsn,
XLogPageReadCB read_page,
XLogReaderRoutine *xl_routine,
LogicalOutputPluginWriterPrepareWrite prepare_write,
LogicalOutputPluginWriterWrite do_write,
LogicalOutputPluginWriterUpdateProgress update_progress)
@ -327,7 +328,7 @@ CreateInitDecodingContext(char *plugin,
ctx = StartupDecodingContext(NIL, restart_lsn, xmin_horizon,
need_full_snapshot, false,
read_page, prepare_write, do_write,
xl_routine, prepare_write, do_write,
update_progress);
/* call output plugin initialization callback */
@ -357,7 +358,10 @@ CreateInitDecodingContext(char *plugin,
* fast_forward
* bypass the generation of logical changes.
*
* read_page, prepare_write, do_write, update_progress
* xl_routine
* XLogReaderRoutine used by underlying xlogreader
*
* prepare_write, do_write, update_progress
* callbacks that have to be filled to perform the use-case dependent,
* actual work.
*
@ -372,7 +376,7 @@ LogicalDecodingContext *
CreateDecodingContext(XLogRecPtr start_lsn,
List *output_plugin_options,
bool fast_forward,
XLogPageReadCB read_page,
XLogReaderRoutine *xl_routine,
LogicalOutputPluginWriterPrepareWrite prepare_write,
LogicalOutputPluginWriterWrite do_write,
LogicalOutputPluginWriterUpdateProgress update_progress)
@ -425,7 +429,7 @@ CreateDecodingContext(XLogRecPtr start_lsn,
ctx = StartupDecodingContext(output_plugin_options,
start_lsn, InvalidTransactionId, false,
fast_forward, read_page, prepare_write,
fast_forward, xl_routine, prepare_write,
do_write, update_progress);
/* call output plugin initialization callback */