Rework XLogReader callback system
authorAlvaro Herrera <alvherre@alvh.no-ip.org>
Fri, 8 May 2020 19:30:34 +0000 (15:30 -0400)
committerAlvaro Herrera <alvherre@alvh.no-ip.org>
Fri, 8 May 2020 19:40:11 +0000 (15:40 -0400)
Code review for 0dc8ead46363, prompted by a bug closed by 91c40548d5f7.

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

13 files changed:
src/backend/access/transam/twophase.c
src/backend/access/transam/xlog.c
src/backend/access/transam/xlogreader.c
src/backend/access/transam/xlogutils.c
src/backend/replication/logical/logical.c
src/backend/replication/logical/logicalfuncs.c
src/backend/replication/slotfuncs.c
src/backend/replication/walsender.c
src/bin/pg_rewind/parsexlog.c
src/bin/pg_waldump/pg_waldump.c
src/include/access/xlogreader.h
src/include/access/xlogutils.h
src/include/replication/logical.h

index 2f7d4ed59a87ce4756d9543a2f3288009f320256..e1904877faa5514de427568ae28d2b57544ad174 100644 (file)
@@ -1331,7 +1331,10 @@ XlogReadTwoPhaseData(XLogRecPtr lsn, char **buf, int *len)
    char       *errormsg;
 
    xlogreader = XLogReaderAllocate(wal_segment_size, NULL,
-                                   &read_local_xlog_page, NULL);
+                                   XL_ROUTINE(.page_read = &read_local_xlog_page,
+                                              .segment_open = &wal_segment_open,
+                                              .segment_close = &wal_segment_close),
+                                   NULL);
    if (!xlogreader)
        ereport(ERROR,
                (errcode(ERRCODE_OUT_OF_MEMORY),
index 0d3d670928430e7972e2c37ac3fe0a689b8b1bbe..a53e6d963346d0e471d6203ae20e8bffd0b7c32e 100644 (file)
@@ -1223,7 +1223,7 @@ XLogInsertRecord(XLogRecData *rdata,
 
        if (!debug_reader)
            debug_reader = XLogReaderAllocate(wal_segment_size, NULL,
-                                             NULL, NULL);
+                                             XL_ROUTINE(), NULL);
 
        if (!debug_reader)
        {
@@ -6478,8 +6478,12 @@ StartupXLOG(void)
 
    /* Set up XLOG reader facility */
    MemSet(&private, 0, sizeof(XLogPageReadPrivate));
-   xlogreader = XLogReaderAllocate(wal_segment_size, NULL,
-                                   &XLogPageRead, &private);
+   xlogreader =
+       XLogReaderAllocate(wal_segment_size, NULL,
+                          XL_ROUTINE(.page_read = &XLogPageRead,
+                                     .segment_open = NULL,
+                                     .segment_close = wal_segment_close),
+                          &private);
    if (!xlogreader)
        ereport(ERROR,
                (errcode(ERRCODE_OUT_OF_MEMORY),
index 79ff976474c76858cd6948311522ef7baa04ea78..7cee8b92c905235dff50946407d989588aabe8cb 100644 (file)
@@ -71,7 +71,7 @@ report_invalid_record(XLogReaderState *state, const char *fmt,...)
  */
 XLogReaderState *
 XLogReaderAllocate(int wal_segment_size, const char *waldir,
-                  XLogPageReadCB pagereadfunc, void *private_data)
+                  XLogReaderRoutine *routine, void *private_data)
 {
    XLogReaderState *state;
 
@@ -81,6 +81,9 @@ XLogReaderAllocate(int wal_segment_size, const char *waldir,
    if (!state)
        return NULL;
 
+   /* initialize caller-provided support functions */
+   state->routine = *routine;
+
    state->max_block_id = -1;
 
    /*
@@ -102,7 +105,6 @@ XLogReaderAllocate(int wal_segment_size, const char *waldir,
    WALOpenSegmentInit(&state->seg, &state->segcxt, wal_segment_size,
                       waldir);
 
-   state->read_page = pagereadfunc;
    /* system_identifier initialized to zeroes above */
    state->private_data = private_data;
    /* ReadRecPtr, EndRecPtr and readLen initialized to zeroes above */
@@ -137,7 +139,7 @@ XLogReaderFree(XLogReaderState *state)
    int         block_id;
 
    if (state->seg.ws_file != -1)
-       close(state->seg.ws_file);
+       state->routine.segment_close(state);
 
    for (block_id = 0; block_id <= XLR_MAX_BLOCK_ID; block_id++)
    {
@@ -250,7 +252,7 @@ XLogBeginRead(XLogReaderState *state, XLogRecPtr RecPtr)
  * XLogBeginRead() or XLogFindNextRecord() must be called before the first call
  * to XLogReadRecord().
  *
- * If the read_page callback fails to read the requested data, NULL is
+ * If the page_read callback fails to read the requested data, NULL is
  * returned.  The callback is expected to have reported the error; errormsg
  * is set to NULL.
  *
@@ -559,10 +561,10 @@ err:
 
 /*
  * Read a single xlog page including at least [pageptr, reqLen] of valid data
- * via the read_page() callback.
+ * via the page_read() callback.
  *
  * Returns -1 if the required page cannot be read for some reason; errormsg_buf
- * is set in that case (unless the error occurs in the read_page callback).
+ * is set in that case (unless the error occurs in the page_read callback).
  *
  * We fetch the page from a reader-local cache if we know we have the required
  * data and if there hasn't been any error since caching the data.
@@ -589,7 +591,7 @@ ReadPageInternal(XLogReaderState *state, XLogRecPtr pageptr, int reqLen)
     * Data is not in our buffer.
     *
     * Every time we actually read the segment, even if we looked at parts of
-    * it before, we need to do verification as the read_page callback might
+    * it before, we need to do verification as the page_read callback might
     * now be rereading data from a different source.
     *
     * Whenever switching to a new WAL segment, we read the first page of the
@@ -601,9 +603,9 @@ ReadPageInternal(XLogReaderState *state, XLogRecPtr pageptr, int reqLen)
    {
        XLogRecPtr  targetSegmentPtr = pageptr - targetPageOff;
 
-       readLen = state->read_page(state, targetSegmentPtr, XLOG_BLCKSZ,
-                                  state->currRecPtr,
-                                  state->readBuf);
+       readLen = state->routine.page_read(state, targetSegmentPtr, XLOG_BLCKSZ,
+                                          state->currRecPtr,
+                                          state->readBuf);
        if (readLen < 0)
            goto err;
 
@@ -619,9 +621,9 @@ ReadPageInternal(XLogReaderState *state, XLogRecPtr pageptr, int reqLen)
     * First, read the requested data length, but at least a short page header
     * so that we can validate it.
     */
-   readLen = state->read_page(state, pageptr, Max(reqLen, SizeOfXLogShortPHD),
-                              state->currRecPtr,
-                              state->readBuf);
+   readLen = state->routine.page_read(state, pageptr, Max(reqLen, SizeOfXLogShortPHD),
+                                      state->currRecPtr,
+                                      state->readBuf);
    if (readLen < 0)
        goto err;
 
@@ -638,9 +640,9 @@ ReadPageInternal(XLogReaderState *state, XLogRecPtr pageptr, int reqLen)
    /* still not enough */
    if (readLen < XLogPageHeaderSize(hdr))
    {
-       readLen = state->read_page(state, pageptr, XLogPageHeaderSize(hdr),
-                                  state->currRecPtr,
-                                  state->readBuf);
+       readLen = state->routine.page_read(state, pageptr, XLogPageHeaderSize(hdr),
+                                          state->currRecPtr,
+                                          state->readBuf);
        if (readLen < 0)
            goto err;
    }
@@ -1041,11 +1043,14 @@ err:
 #endif                         /* FRONTEND */
 
 /*
+ * Helper function to ease writing of XLogRoutine->page_read callbacks.
+ * If this function is used, caller must supply an open_segment callback in
+ * 'state', as that is used here.
+ *
  * Read 'count' bytes into 'buf', starting at location 'startptr', from WAL
  * fetched from timeline 'tli'.
  *
- * 'seg/segcxt' identify the last segment used.  'openSegment' is a callback
- * to open the next segment, if necessary.
+ * 'seg/segcxt' identify the last segment used.
  *
  * Returns true if succeeded, false if an error occurs, in which case
  * 'errinfo' receives error details.
@@ -1054,9 +1059,10 @@ err:
  * WAL buffers when possible.
  */
 bool
-WALRead(char *buf, XLogRecPtr startptr, Size count, TimeLineID tli,
+WALRead(XLogReaderState *state,
+       char *buf, XLogRecPtr startptr, Size count, TimeLineID tli,
        WALOpenSegment *seg, WALSegmentContext *segcxt,
-       WALSegmentOpen openSegment, WALReadError *errinfo)
+       WALReadError *errinfo)
 {
    char       *p;
    XLogRecPtr  recptr;
@@ -1086,10 +1092,11 @@ WALRead(char *buf, XLogRecPtr startptr, Size count, TimeLineID tli,
            XLogSegNo   nextSegNo;
 
            if (seg->ws_file >= 0)
-               close(seg->ws_file);
+               state->routine.segment_close(state);
 
            XLByteToSeg(recptr, nextSegNo, segcxt->ws_segsize);
-           seg->ws_file = openSegment(nextSegNo, segcxt, &tli);
+           seg->ws_file = state->routine.segment_open(state, nextSegNo,
+                                                      segcxt, &tli);
 
            /* Update the current segment info. */
            seg->ws_tli = tli;
index 6cb143e161d144a3c5885038d208c1bcd5d42d3c..bbd801513a89fb1fb97de092ecf25e700938c352 100644 (file)
@@ -783,10 +783,10 @@ XLogReadDetermineTimeline(XLogReaderState *state, XLogRecPtr wantPage, uint32 wa
    }
 }
 
-/* openSegment callback for WALRead */
-static int
-wal_segment_open(XLogSegNo nextSegNo, WALSegmentContext * segcxt,
-                TimeLineID *tli_p)
+/* XLogReaderRoutine->segment_open callback for local pg_wal files */
+int
+wal_segment_open(XLogReaderState *state, XLogSegNo nextSegNo,
+                WALSegmentContext *segcxt, TimeLineID *tli_p)
 {
    TimeLineID  tli = *tli_p;
    char        path[MAXPGPATH];
@@ -811,8 +811,17 @@ wal_segment_open(XLogSegNo nextSegNo, WALSegmentContext * segcxt,
    return -1;                  /* keep compiler quiet */
 }
 
+/* stock XLogReaderRoutine->segment_close callback */
+void
+wal_segment_close(XLogReaderState *state)
+{
+   close(state->seg.ws_file);
+   /* need to check errno? */
+   state->seg.ws_file = -1;
+}
+
 /*
- * read_page callback for reading local xlog files
+ * XLogReaderRoutine->page_read callback for reading local xlog files
  *
  * Public because it would likely be very helpful for someone writing another
  * output method outside walsender, e.g. in a bgworker.
@@ -937,8 +946,9 @@ read_local_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr,
     * as 'count', read the whole page anyway. It's guaranteed to be
     * zero-padded up to the page boundary if it's incomplete.
     */
-   if (!WALRead(cur_page, targetPagePtr, XLOG_BLCKSZ, tli, &state->seg,
-                &state->segcxt, wal_segment_open, &errinfo))
+   if (!WALRead(state, cur_page, targetPagePtr, XLOG_BLCKSZ, tli,
+                &state->seg, &state->segcxt,
+                &errinfo))
        WALReadRaiseError(&errinfo);
 
    /* number of valid bytes in the buffer */
index 5adf253583b1cfc7dc4e0586afd834a1f4bf68bd..dc69e5ce5f32cdedb8e18c720c579f20e929997f 100644 (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 */
index fded8e82908b9aa19e5d9243007d03da9fb54711..b99c94e84891a4f9d7cd88c6af667743a64fb25b 100644 (file)
@@ -233,7 +233,9 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
        ctx = CreateDecodingContext(InvalidXLogRecPtr,
                                    options,
                                    false,
-                                   read_local_xlog_page,
+                                   XL_ROUTINE(.page_read = read_local_xlog_page,
+                                              .segment_open = wal_segment_open,
+                                              .segment_close = wal_segment_close),
                                    LogicalOutputPrepareWrite,
                                    LogicalOutputWrite, NULL);
 
index ae751e94e765f2333ddf9a40675f13c9661d12c5..26890dffb456de506bd011c7026e537afc7a0851 100644 (file)
@@ -152,8 +152,10 @@ create_logical_replication_slot(char *name, char *plugin,
    ctx = CreateInitDecodingContext(plugin, NIL,
                                    false,  /* just catalogs is OK */
                                    restart_lsn,
-                                   read_local_xlog_page, NULL, NULL,
-                                   NULL);
+                                   XL_ROUTINE(.page_read = read_local_xlog_page,
+                                              .segment_open = wal_segment_open,
+                                              .segment_close = wal_segment_close),
+                                   NULL, NULL, NULL);
 
    /*
     * If caller needs us to determine the decoding start point, do so now.
@@ -464,7 +466,9 @@ pg_logical_replication_slot_advance(XLogRecPtr moveto)
        ctx = CreateDecodingContext(InvalidXLogRecPtr,
                                    NIL,
                                    true,   /* fast_forward */
-                                   read_local_xlog_page,
+                                   XL_ROUTINE(.page_read = read_local_xlog_page,
+                                              .segment_open = wal_segment_open,
+                                              .segment_close = wal_segment_close),
                                    NULL, NULL, NULL);
 
        /*
index 8b55bbfcb2ec31b2859bf03f87d5bbc9b19c0412..d18475b8540605eca44a22b52e29658726c9ade2 100644 (file)
@@ -54,8 +54,8 @@
 #include "access/transam.h"
 #include "access/xact.h"
 #include "access/xlog_internal.h"
+#include "access/xlogreader.h"
 #include "access/xlogutils.h"
-
 #include "catalog/pg_authid.h"
 #include "catalog/pg_type.h"
 #include "commands/dbcommands.h"
@@ -248,8 +248,8 @@ static void LagTrackerWrite(XLogRecPtr lsn, TimestampTz local_flush_time);
 static TimeOffset LagTrackerRead(int head, XLogRecPtr lsn, TimestampTz now);
 static bool TransactionIdInRecentPast(TransactionId xid, uint32 epoch);
 
-static int WalSndSegmentOpen(XLogSegNo nextSegNo, WALSegmentContext *segcxt,
-                             TimeLineID *tli_p);
+static int WalSndSegmentOpen(XLogReaderState *state, XLogSegNo nextSegNo,
+                             WALSegmentContext *segcxt, TimeLineID *tli_p);
 static void UpdateSpillStats(LogicalDecodingContext *ctx);
 
 
@@ -798,7 +798,8 @@ StartReplication(StartReplicationCmd *cmd)
 }
 
 /*
- * read_page callback for logical decoding contexts, as a walsender process.
+ * XLogReaderRoutine->page_read callback for logical decoding contexts, as a
+ * walsender process.
  *
  * Inside the walsender we can do better than read_local_xlog_page,
  * which has to do a plain sleep/busy loop, because the walsender's latch gets
@@ -832,7 +833,8 @@ logical_read_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, int req
        count = flushptr - targetPagePtr;   /* part of the page available */
 
    /* now actually read the data, we know it's there */
-   if (!WALRead(cur_page,
+   if (!WALRead(state,
+                cur_page,
                 targetPagePtr,
                 XLOG_BLCKSZ,
                 sendSeg->ws_tli,   /* Pass the current TLI because only
@@ -840,7 +842,6 @@ logical_read_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, int req
                                     * TLI is needed. */
                 sendSeg,
                 sendCxt,
-                WalSndSegmentOpen,
                 &errinfo))
        WALReadRaiseError(&errinfo);
 
@@ -1005,7 +1006,9 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
        ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
                                        InvalidXLogRecPtr,
-                                       logical_read_xlog_page,
+                                       XL_ROUTINE(.page_read = logical_read_xlog_page,
+                                                  .segment_open = WalSndSegmentOpen,
+                                                  .segment_close = wal_segment_close),
                                        WalSndPrepareWrite, WalSndWriteData,
                                        WalSndUpdateProgress);
 
@@ -1168,7 +1171,9 @@ StartLogicalReplication(StartReplicationCmd *cmd)
     */
    logical_decoding_ctx =
        CreateDecodingContext(cmd->startpoint, cmd->options, false,
-                             logical_read_xlog_page,
+                             XL_ROUTINE(.page_read = logical_read_xlog_page,
+                                        .segment_open = WalSndSegmentOpen,
+                                        .segment_close = wal_segment_close),
                              WalSndPrepareWrite, WalSndWriteData,
                              WalSndUpdateProgress);
 
@@ -2441,9 +2446,10 @@ WalSndKill(int code, Datum arg)
    SpinLockRelease(&walsnd->mutex);
 }
 
-/* walsender's openSegment callback for WALRead */
+/* XLogReaderRoutine->segment_open callback */
 static int
-WalSndSegmentOpen(XLogSegNo nextSegNo, WALSegmentContext *segcxt,
+WalSndSegmentOpen(XLogReaderState *state,
+                 XLogSegNo nextSegNo, WALSegmentContext *segcxt,
                  TimeLineID *tli_p)
 {
    char        path[MAXPGPATH];
@@ -2531,6 +2537,12 @@ XLogSendPhysical(void)
    Size        nbytes;
    XLogSegNo   segno;
    WALReadError errinfo;
+   static XLogReaderState fake_xlogreader =
+   {
+       /* Fake xlogreader state for WALRead */
+       .routine.segment_open = WalSndSegmentOpen,
+       .routine.segment_close = wal_segment_close
+   };
 
    /* If requested switch the WAL sender to the stopping state. */
    if (got_STOPPING)
@@ -2748,7 +2760,8 @@ XLogSendPhysical(void)
    enlargeStringInfo(&output_message, nbytes);
 
 retry:
-   if (!WALRead(&output_message.data[output_message.len],
+   if (!WALRead(&fake_xlogreader,
+                &output_message.data[output_message.len],
                 startptr,
                 nbytes,
                 sendSeg->ws_tli,   /* Pass the current TLI because only
@@ -2756,7 +2769,6 @@ retry:
                                     * TLI is needed. */
                 sendSeg,
                 sendCxt,
-                WalSndSegmentOpen,
                 &errinfo))
        WALReadRaiseError(&errinfo);
 
index c51b5db315aab812f00a7afb7f8de4a7632e94da..d637f5eb7715ad000ff954c4ae8bd4c9809611be 100644 (file)
@@ -66,7 +66,8 @@ extractPageMap(const char *datadir, XLogRecPtr startpoint, int tliIndex,
 
    private.tliIndex = tliIndex;
    private.restoreCommand = restoreCommand;
-   xlogreader = XLogReaderAllocate(WalSegSz, datadir, &SimpleXLogPageRead,
+   xlogreader = XLogReaderAllocate(WalSegSz, datadir,
+                                   XL_ROUTINE(.page_read = &SimpleXLogPageRead),
                                    &private);
    if (xlogreader == NULL)
        pg_fatal("out of memory");
@@ -117,7 +118,8 @@ readOneRecord(const char *datadir, XLogRecPtr ptr, int tliIndex,
 
    private.tliIndex = tliIndex;
    private.restoreCommand = restoreCommand;
-   xlogreader = XLogReaderAllocate(WalSegSz, datadir, &SimpleXLogPageRead,
+   xlogreader = XLogReaderAllocate(WalSegSz, datadir,
+                                   XL_ROUTINE(.page_read = &SimpleXLogPageRead),
                                    &private);
    if (xlogreader == NULL)
        pg_fatal("out of memory");
@@ -176,7 +178,8 @@ findLastCheckpoint(const char *datadir, XLogRecPtr forkptr, int tliIndex,
 
    private.tliIndex = tliIndex;
    private.restoreCommand = restoreCommand;
-   xlogreader = XLogReaderAllocate(WalSegSz, datadir, &SimpleXLogPageRead,
+   xlogreader = XLogReaderAllocate(WalSegSz, datadir,
+                                   XL_ROUTINE(.page_read = &SimpleXLogPageRead),
                                    &private);
    if (xlogreader == NULL)
        pg_fatal("out of memory");
index d7bd9ccac24d6d1c9ac3a853b5e3b9e13a970e17..e29f65500fb630afde0b9eea1a888e866ac95243 100644 (file)
@@ -279,9 +279,10 @@ identify_target_directory(char *directory, char *fname)
    return NULL;                /* not reached */
 }
 
-/* pg_waldump's openSegment callback for WALRead */
+/* pg_waldump's XLogReaderRoutine->segment_open callback */
 static int
-WALDumpOpenSegment(XLogSegNo nextSegNo, WALSegmentContext *segcxt,
+WALDumpOpenSegment(XLogReaderState *state,
+                  XLogSegNo nextSegNo, WALSegmentContext *segcxt,
                   TimeLineID *tli_p)
 {
    TimeLineID  tli = *tli_p;
@@ -321,8 +322,18 @@ WALDumpOpenSegment(XLogSegNo nextSegNo, WALSegmentContext *segcxt,
 }
 
 /*
- * XLogReader read_page callback
+ * pg_waldump's XLogReaderRoutine->segment_close callback.  Same as
+ * wal_segment_close
  */
+static void
+WALDumpCloseSegment(XLogReaderState *state)
+{
+   close(state->seg.ws_file);
+   /* need to check errno? */
+   state->seg.ws_file = -1;
+}
+
+/* pg_waldump's XLogReaderRoutine->page_read callback */
 static int
 WALDumpReadPage(XLogReaderState *state, XLogRecPtr targetPagePtr, int reqLen,
                XLogRecPtr targetPtr, char *readBuff)
@@ -344,8 +355,9 @@ WALDumpReadPage(XLogReaderState *state, XLogRecPtr targetPagePtr, int reqLen,
        }
    }
 
-   if (!WALRead(readBuff, targetPagePtr, count, private->timeline,
-                &state->seg, &state->segcxt, WALDumpOpenSegment, &errinfo))
+   if (!WALRead(state, readBuff, targetPagePtr, count, private->timeline,
+                &state->seg, &state->segcxt,
+                &errinfo))
    {
        WALOpenSegment *seg = &errinfo.wre_seg;
        char        fname[MAXPGPATH];
@@ -1031,8 +1043,12 @@ main(int argc, char **argv)
    /* done with argument parsing, do the actual work */
 
    /* we have everything we need, start reading */
-   xlogreader_state = XLogReaderAllocate(WalSegSz, waldir, WALDumpReadPage,
-                                         &private);
+   xlogreader_state =
+       XLogReaderAllocate(WalSegSz, waldir,
+                          XL_ROUTINE(.page_read = WALDumpReadPage,
+                                     .segment_open = WALDumpOpenSegment,
+                                     .segment_close = WALDumpCloseSegment),
+                          &private);
    if (!xlogreader_state)
        fatal_error("out of memory");
 
index 4582196e1851ad7f5454c901c46e1c434300e277..81af200f5e644192479aadf989a384ff894dc2bb 100644 (file)
  *     XLogBeginRead() or XLogFindNextRecord(), and call XLogReadRecord()
  *     until it returns NULL.
  *
+ *     Callers supply a page_read callback if they want to to call
+ *     XLogReadRecord or XLogFindNextRecord; it can be passed in as NULL
+ *     otherwise.  The WALRead function can be used as a helper to write
+ *     page_read callbacks, but it is not mandatory; callers that use it,
+ *     must supply open_segment callbacks.  The close_segment callback
+ *     must always be supplied.
+ *
  *     After reading a record with XLogReadRecord(), it's decomposed into
  *     the per-block and main data parts, and the parts can be accessed
  *     with the XLogRec* macros and functions. You can also decode a
@@ -50,12 +57,69 @@ typedef struct WALSegmentContext
 
 typedef struct XLogReaderState XLogReaderState;
 
-/* Function type definition for the read_page callback */
+/* Function type definitions for various xlogreader interactions */
 typedef int (*XLogPageReadCB) (XLogReaderState *xlogreader,
                               XLogRecPtr targetPagePtr,
                               int reqLen,
                               XLogRecPtr targetRecPtr,
                               char *readBuf);
+typedef int (*WALSegmentOpenCB) (XLogReaderState *xlogreader,
+                                XLogSegNo nextSegNo,
+                                WALSegmentContext *segcxt,
+                                TimeLineID *tli_p);
+typedef void (*WALSegmentCloseCB) (XLogReaderState *xlogreader);
+
+typedef struct XLogReaderRoutine
+{
+   /*
+    * Data input callback
+    *
+    * This callback shall read at least reqLen valid bytes of the xlog page
+    * starting at targetPagePtr, and store them in readBuf.  The callback
+    * shall return the number of bytes read (never more than XLOG_BLCKSZ), or
+    * -1 on failure.  The callback shall sleep, if necessary, to wait for the
+    * requested bytes to become available.  The callback will not be invoked
+    * again for the same page unless more than the returned number of bytes
+    * are needed.
+    *
+    * targetRecPtr is the position of the WAL record we're reading.  Usually
+    * it is equal to targetPagePtr + reqLen, but sometimes xlogreader needs
+    * to read and verify the page or segment header, before it reads the
+    * actual WAL record it's interested in.  In that case, targetRecPtr can
+    * be used to determine which timeline to read the page from.
+    *
+    * The callback shall set ->seg.ws_tli to the TLI of the file the page was
+    * read from.
+    */
+   XLogPageReadCB page_read;
+
+   /*
+    * Callback to open the specified WAL segment for reading.  The file
+    * descriptor of the opened segment shall be returned.  In case of
+    * failure, an error shall be raised by the callback and it shall not
+    * return.
+    *
+    * "nextSegNo" is the number of the segment to be opened.
+    *
+    * "segcxt" is additional information about the segment.
+    *
+    * "tli_p" is an input/output argument. XLogRead() uses it to pass the
+    * timeline in which the new segment should be found, but the callback can
+    * use it to return the TLI that it actually opened.
+    *
+    * BasicOpenFile() is the preferred way to open the segment file in
+    * backend code, whereas open(2) should be used in frontend.
+    */
+   WALSegmentOpenCB segment_open;
+
+   /*
+    * WAL segment close callback.  ->seg.ws_file shall be set to a negative
+    * number.
+    */
+   WALSegmentCloseCB segment_close;
+} XLogReaderRoutine;
+
+#define XL_ROUTINE(...) &(XLogReaderRoutine){__VA_ARGS__}
 
 typedef struct
 {
@@ -88,33 +152,16 @@ typedef struct
 
 struct XLogReaderState
 {
+   /*
+    * Operational callbacks
+    */
+   XLogReaderRoutine routine;
+
    /* ----------------------------------------
     * Public parameters
     * ----------------------------------------
     */
 
-   /*
-    * Data input callback (mandatory).
-    *
-    * This callback shall read at least reqLen valid bytes of the xlog page
-    * starting at targetPagePtr, and store them in readBuf.  The callback
-    * shall return the number of bytes read (never more than XLOG_BLCKSZ), or
-    * -1 on failure.  The callback shall sleep, if necessary, to wait for the
-    * requested bytes to become available.  The callback will not be invoked
-    * again for the same page unless more than the returned number of bytes
-    * are needed.
-    *
-    * targetRecPtr is the position of the WAL record we're reading.  Usually
-    * it is equal to targetPagePtr + reqLen, but sometimes xlogreader needs
-    * to read and verify the page or segment header, before it reads the
-    * actual WAL record it's interested in.  In that case, targetRecPtr can
-    * be used to determine which timeline to read the page from.
-    *
-    * The callback shall set ->seg.ws_tli to the TLI of the file the page was
-    * read from.
-    */
-   XLogPageReadCB read_page;
-
    /*
     * System identifier of the xlog files we're about to read.  Set to zero
     * (the default value) if unknown or unimportant.
@@ -214,30 +261,13 @@ struct XLogReaderState
 /* Get a new XLogReader */
 extern XLogReaderState *XLogReaderAllocate(int wal_segment_size,
                                           const char *waldir,
-                                          XLogPageReadCB pagereadfunc,
+                                          XLogReaderRoutine *routine,
                                           void *private_data);
+extern XLogReaderRoutine *LocalXLogReaderRoutine(void);
 
 /* Free an XLogReader */
 extern void XLogReaderFree(XLogReaderState *state);
 
-/*
- * Callback to open the specified WAL segment for reading.  Returns a valid
- * file descriptor when the file was opened successfully.
- *
- * "nextSegNo" is the number of the segment to be opened.
- *
- * "segcxt" is additional information about the segment.
- *
- * "tli_p" is an input/output argument. XLogRead() uses it to pass the
- * timeline in which the new segment should be found, but the callback can use
- * it to return the TLI that it actually opened.
- *
- * BasicOpenFile() is the preferred way to open the segment file in backend
- * code, whereas open(2) should be used in frontend.
- */
-typedef int (*WALSegmentOpen) (XLogSegNo nextSegNo, WALSegmentContext *segcxt,
-                              TimeLineID *tli_p);
-
 /* Initialize supporting structures */
 extern void WALOpenSegmentInit(WALOpenSegment *seg, WALSegmentContext *segcxt,
                               int segsize, const char *waldir);
@@ -269,9 +299,10 @@ typedef struct WALReadError
    WALOpenSegment wre_seg;     /* Segment we tried to read from. */
 } WALReadError;
 
-extern bool WALRead(char *buf, XLogRecPtr startptr, Size count,
+extern bool WALRead(XLogReaderState *state,
+                   char *buf, XLogRecPtr startptr, Size count,
                    TimeLineID tli, WALOpenSegment *seg,
-                   WALSegmentContext *segcxt, WALSegmentOpen openSegment,
+                   WALSegmentContext *segcxt,
                    WALReadError *errinfo);
 
 /* Functions for decoding an XLogRecord */
index 5181a077d964d6201dece864b0aeb7675e922166..68ce815476ca618f642ccc945a6f4172f8ba9eeb 100644 (file)
@@ -50,6 +50,11 @@ extern void FreeFakeRelcacheEntry(Relation fakerel);
 extern int read_local_xlog_page(XLogReaderState *state,
                                 XLogRecPtr targetPagePtr, int reqLen,
                                 XLogRecPtr targetRecPtr, char *cur_page);
+extern int wal_segment_open(XLogReaderState *state,
+                            XLogSegNo nextSegNo,
+                            WALSegmentContext *segcxt,
+                            TimeLineID *tli_p);
+extern void wal_segment_close(XLogReaderState *state);
 
 extern void XLogReadDetermineTimeline(XLogReaderState *state,
                                      XLogRecPtr wantPage, uint32 wantLength);
index 3b7ca7f1da47e814702b7aca2ad653b7190758c1..c2f2475e5d3e5f193f46e9a5ceaf3a017deaca91 100644 (file)
@@ -95,14 +95,14 @@ extern LogicalDecodingContext *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);
 extern 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);