mirror of
https://git.postgresql.org/git/postgresql.git
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1022 lines
31 KiB
C
1022 lines
31 KiB
C
/*-------------------------------------------------------------------------
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*
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* xlogutils.c
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*
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* PostgreSQL write-ahead log manager utility routines
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*
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* This file contains support routines that are used by XLOG replay functions.
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* None of this code is used during normal system operation.
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*
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*
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* Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/backend/access/transam/xlogutils.c
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include <unistd.h>
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#include "access/timeline.h"
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#include "access/xlog.h"
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#include "access/xlog_internal.h"
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#include "access/xlogutils.h"
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#include "catalog/catalog.h"
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#include "miscadmin.h"
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#include "pgstat.h"
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#include "storage/smgr.h"
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#include "utils/guc.h"
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#include "utils/hsearch.h"
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#include "utils/rel.h"
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/*
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* During XLOG replay, we may see XLOG records for incremental updates of
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* pages that no longer exist, because their relation was later dropped or
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* truncated. (Note: this is only possible when full_page_writes = OFF,
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* since when it's ON, the first reference we see to a page should always
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* be a full-page rewrite not an incremental update.) Rather than simply
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* ignoring such records, we make a note of the referenced page, and then
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* complain if we don't actually see a drop or truncate covering the page
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* later in replay.
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*/
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typedef struct xl_invalid_page_key
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{
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RelFileNode node; /* the relation */
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ForkNumber forkno; /* the fork number */
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BlockNumber blkno; /* the page */
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} xl_invalid_page_key;
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typedef struct xl_invalid_page
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{
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xl_invalid_page_key key; /* hash key ... must be first */
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bool present; /* page existed but contained zeroes */
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} xl_invalid_page;
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static HTAB *invalid_page_tab = NULL;
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/* Report a reference to an invalid page */
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static void
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report_invalid_page(int elevel, RelFileNode node, ForkNumber forkno,
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BlockNumber blkno, bool present)
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{
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char *path = relpathperm(node, forkno);
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if (present)
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elog(elevel, "page %u of relation %s is uninitialized",
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blkno, path);
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else
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elog(elevel, "page %u of relation %s does not exist",
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blkno, path);
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pfree(path);
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}
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/* Log a reference to an invalid page */
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static void
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log_invalid_page(RelFileNode node, ForkNumber forkno, BlockNumber blkno,
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bool present)
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{
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xl_invalid_page_key key;
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xl_invalid_page *hentry;
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bool found;
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/*
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* Once recovery has reached a consistent state, the invalid-page table
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* should be empty and remain so. If a reference to an invalid page is
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* found after consistency is reached, PANIC immediately. This might seem
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* aggressive, but it's better than letting the invalid reference linger
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* in the hash table until the end of recovery and PANIC there, which
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* might come only much later if this is a standby server.
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*/
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if (reachedConsistency)
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{
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report_invalid_page(WARNING, node, forkno, blkno, present);
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elog(PANIC, "WAL contains references to invalid pages");
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}
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/*
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* Log references to invalid pages at DEBUG1 level. This allows some
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* tracing of the cause (note the elog context mechanism will tell us
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* something about the XLOG record that generated the reference).
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*/
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if (log_min_messages <= DEBUG1 || client_min_messages <= DEBUG1)
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report_invalid_page(DEBUG1, node, forkno, blkno, present);
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if (invalid_page_tab == NULL)
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{
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/* create hash table when first needed */
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HASHCTL ctl;
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memset(&ctl, 0, sizeof(ctl));
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ctl.keysize = sizeof(xl_invalid_page_key);
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ctl.entrysize = sizeof(xl_invalid_page);
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invalid_page_tab = hash_create("XLOG invalid-page table",
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100,
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&ctl,
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HASH_ELEM | HASH_BLOBS);
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}
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/* we currently assume xl_invalid_page_key contains no padding */
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key.node = node;
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key.forkno = forkno;
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key.blkno = blkno;
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hentry = (xl_invalid_page *)
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hash_search(invalid_page_tab, (void *) &key, HASH_ENTER, &found);
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if (!found)
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{
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/* hash_search already filled in the key */
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hentry->present = present;
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}
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else
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{
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/* repeat reference ... leave "present" as it was */
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}
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}
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/* Forget any invalid pages >= minblkno, because they've been dropped */
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static void
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forget_invalid_pages(RelFileNode node, ForkNumber forkno, BlockNumber minblkno)
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{
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HASH_SEQ_STATUS status;
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xl_invalid_page *hentry;
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if (invalid_page_tab == NULL)
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return; /* nothing to do */
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hash_seq_init(&status, invalid_page_tab);
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while ((hentry = (xl_invalid_page *) hash_seq_search(&status)) != NULL)
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{
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if (RelFileNodeEquals(hentry->key.node, node) &&
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hentry->key.forkno == forkno &&
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hentry->key.blkno >= minblkno)
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{
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if (log_min_messages <= DEBUG2 || client_min_messages <= DEBUG2)
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{
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char *path = relpathperm(hentry->key.node, forkno);
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elog(DEBUG2, "page %u of relation %s has been dropped",
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hentry->key.blkno, path);
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pfree(path);
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}
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if (hash_search(invalid_page_tab,
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(void *) &hentry->key,
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HASH_REMOVE, NULL) == NULL)
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elog(ERROR, "hash table corrupted");
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}
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}
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}
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/* Forget any invalid pages in a whole database */
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static void
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forget_invalid_pages_db(Oid dbid)
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{
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HASH_SEQ_STATUS status;
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xl_invalid_page *hentry;
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if (invalid_page_tab == NULL)
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return; /* nothing to do */
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hash_seq_init(&status, invalid_page_tab);
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while ((hentry = (xl_invalid_page *) hash_seq_search(&status)) != NULL)
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{
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if (hentry->key.node.dbNode == dbid)
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{
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if (log_min_messages <= DEBUG2 || client_min_messages <= DEBUG2)
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{
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char *path = relpathperm(hentry->key.node, hentry->key.forkno);
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elog(DEBUG2, "page %u of relation %s has been dropped",
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hentry->key.blkno, path);
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pfree(path);
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}
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if (hash_search(invalid_page_tab,
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(void *) &hentry->key,
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HASH_REMOVE, NULL) == NULL)
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elog(ERROR, "hash table corrupted");
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}
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}
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}
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/* Are there any unresolved references to invalid pages? */
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bool
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XLogHaveInvalidPages(void)
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{
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if (invalid_page_tab != NULL &&
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hash_get_num_entries(invalid_page_tab) > 0)
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return true;
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return false;
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}
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/* Complain about any remaining invalid-page entries */
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void
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XLogCheckInvalidPages(void)
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{
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HASH_SEQ_STATUS status;
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xl_invalid_page *hentry;
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bool foundone = false;
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if (invalid_page_tab == NULL)
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return; /* nothing to do */
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hash_seq_init(&status, invalid_page_tab);
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/*
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* Our strategy is to emit WARNING messages for all remaining entries and
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* only PANIC after we've dumped all the available info.
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*/
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while ((hentry = (xl_invalid_page *) hash_seq_search(&status)) != NULL)
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{
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report_invalid_page(WARNING, hentry->key.node, hentry->key.forkno,
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hentry->key.blkno, hentry->present);
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foundone = true;
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}
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if (foundone)
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elog(PANIC, "WAL contains references to invalid pages");
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hash_destroy(invalid_page_tab);
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invalid_page_tab = NULL;
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}
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/*
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* XLogReadBufferForRedo
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* Read a page during XLOG replay
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*
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* Reads a block referenced by a WAL record into shared buffer cache, and
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* determines what needs to be done to redo the changes to it. If the WAL
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* record includes a full-page image of the page, it is restored.
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*
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* 'lsn' is the LSN of the record being replayed. It is compared with the
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* page's LSN to determine if the record has already been replayed.
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* 'block_id' is the ID number the block was registered with, when the WAL
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* record was created.
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*
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* Returns one of the following:
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*
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* BLK_NEEDS_REDO - changes from the WAL record need to be applied
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* BLK_DONE - block doesn't need replaying
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* BLK_RESTORED - block was restored from a full-page image included in
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* the record
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* BLK_NOTFOUND - block was not found (because it was truncated away by
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* an operation later in the WAL stream)
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*
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* On return, the buffer is locked in exclusive-mode, and returned in *buf.
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* Note that the buffer is locked and returned even if it doesn't need
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* replaying. (Getting the buffer lock is not really necessary during
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* single-process crash recovery, but some subroutines such as MarkBufferDirty
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* will complain if we don't have the lock. In hot standby mode it's
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* definitely necessary.)
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*
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* Note: when a backup block is available in XLOG with the BKPIMAGE_APPLY flag
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* set, we restore it, even if the page in the database appears newer. This
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* is to protect ourselves against database pages that were partially or
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* incorrectly written during a crash. We assume that the XLOG data must be
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* good because it has passed a CRC check, while the database page might not
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* be. This will force us to replay all subsequent modifications of the page
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* that appear in XLOG, rather than possibly ignoring them as already
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* applied, but that's not a huge drawback.
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*/
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XLogRedoAction
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XLogReadBufferForRedo(XLogReaderState *record, uint8 block_id,
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Buffer *buf)
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{
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return XLogReadBufferForRedoExtended(record, block_id, RBM_NORMAL,
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false, buf);
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}
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/*
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* Pin and lock a buffer referenced by a WAL record, for the purpose of
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* re-initializing it.
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*/
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Buffer
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XLogInitBufferForRedo(XLogReaderState *record, uint8 block_id)
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{
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Buffer buf;
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XLogReadBufferForRedoExtended(record, block_id, RBM_ZERO_AND_LOCK, false,
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&buf);
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return buf;
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}
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/*
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* XLogReadBufferForRedoExtended
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* Like XLogReadBufferForRedo, but with extra options.
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*
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* In RBM_ZERO_* modes, if the page doesn't exist, the relation is extended
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* with all-zeroes pages up to the referenced block number. In
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* RBM_ZERO_AND_LOCK and RBM_ZERO_AND_CLEANUP_LOCK modes, the return value
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* is always BLK_NEEDS_REDO.
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*
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* (The RBM_ZERO_AND_CLEANUP_LOCK mode is redundant with the get_cleanup_lock
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* parameter. Do not use an inconsistent combination!)
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*
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* If 'get_cleanup_lock' is true, a "cleanup lock" is acquired on the buffer
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* using LockBufferForCleanup(), instead of a regular exclusive lock.
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*/
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XLogRedoAction
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XLogReadBufferForRedoExtended(XLogReaderState *record,
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uint8 block_id,
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ReadBufferMode mode, bool get_cleanup_lock,
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Buffer *buf)
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{
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XLogRecPtr lsn = record->EndRecPtr;
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RelFileNode rnode;
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ForkNumber forknum;
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BlockNumber blkno;
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Page page;
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bool zeromode;
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bool willinit;
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if (!XLogRecGetBlockTag(record, block_id, &rnode, &forknum, &blkno))
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{
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/* Caller specified a bogus block_id */
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elog(PANIC, "failed to locate backup block with ID %d", block_id);
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}
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/*
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* Make sure that if the block is marked with WILL_INIT, the caller is
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* going to initialize it. And vice versa.
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*/
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zeromode = (mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK);
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willinit = (record->blocks[block_id].flags & BKPBLOCK_WILL_INIT) != 0;
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if (willinit && !zeromode)
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elog(PANIC, "block with WILL_INIT flag in WAL record must be zeroed by redo routine");
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if (!willinit && zeromode)
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elog(PANIC, "block to be initialized in redo routine must be marked with WILL_INIT flag in the WAL record");
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/* If it has a full-page image and it should be restored, do it. */
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if (XLogRecBlockImageApply(record, block_id))
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{
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Assert(XLogRecHasBlockImage(record, block_id));
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*buf = XLogReadBufferExtended(rnode, forknum, blkno,
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get_cleanup_lock ? RBM_ZERO_AND_CLEANUP_LOCK : RBM_ZERO_AND_LOCK);
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page = BufferGetPage(*buf);
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if (!RestoreBlockImage(record, block_id, page))
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elog(ERROR, "failed to restore block image");
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/*
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* The page may be uninitialized. If so, we can't set the LSN because
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* that would corrupt the page.
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*/
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if (!PageIsNew(page))
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{
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PageSetLSN(page, lsn);
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}
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MarkBufferDirty(*buf);
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/*
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* At the end of crash recovery the init forks of unlogged relations
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* are copied, without going through shared buffers. So we need to
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* force the on-disk state of init forks to always be in sync with the
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* state in shared buffers.
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*/
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if (forknum == INIT_FORKNUM)
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FlushOneBuffer(*buf);
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return BLK_RESTORED;
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}
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else
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{
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*buf = XLogReadBufferExtended(rnode, forknum, blkno, mode);
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if (BufferIsValid(*buf))
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{
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if (mode != RBM_ZERO_AND_LOCK && mode != RBM_ZERO_AND_CLEANUP_LOCK)
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{
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if (get_cleanup_lock)
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LockBufferForCleanup(*buf);
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else
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LockBuffer(*buf, BUFFER_LOCK_EXCLUSIVE);
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}
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if (lsn <= PageGetLSN(BufferGetPage(*buf)))
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return BLK_DONE;
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else
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return BLK_NEEDS_REDO;
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}
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else
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return BLK_NOTFOUND;
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}
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}
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/*
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* XLogReadBufferExtended
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* Read a page during XLOG replay
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*
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* This is functionally comparable to ReadBufferExtended. There's some
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* differences in the behavior wrt. the "mode" argument:
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*
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* In RBM_NORMAL mode, if the page doesn't exist, or contains all-zeroes, we
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* return InvalidBuffer. In this case the caller should silently skip the
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* update on this page. (In this situation, we expect that the page was later
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* dropped or truncated. If we don't see evidence of that later in the WAL
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* sequence, we'll complain at the end of WAL replay.)
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*
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* In RBM_ZERO_* modes, if the page doesn't exist, the relation is extended
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* with all-zeroes pages up to the given block number.
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*
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* In RBM_NORMAL_NO_LOG mode, we return InvalidBuffer if the page doesn't
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* exist, and we don't check for all-zeroes. Thus, no log entry is made
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* to imply that the page should be dropped or truncated later.
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*
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* NB: A redo function should normally not call this directly. To get a page
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* to modify, use XLogReadBufferForRedoExtended instead. It is important that
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* all pages modified by a WAL record are registered in the WAL records, or
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* they will be invisible to tools that that need to know which pages are
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* modified.
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*/
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Buffer
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XLogReadBufferExtended(RelFileNode rnode, ForkNumber forknum,
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BlockNumber blkno, ReadBufferMode mode)
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{
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BlockNumber lastblock;
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Buffer buffer;
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SMgrRelation smgr;
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Assert(blkno != P_NEW);
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/* Open the relation at smgr level */
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smgr = smgropen(rnode, InvalidBackendId);
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/*
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* Create the target file if it doesn't already exist. This lets us cope
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* if the replay sequence contains writes to a relation that is later
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* deleted. (The original coding of this routine would instead suppress
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* the writes, but that seems like it risks losing valuable data if the
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* filesystem loses an inode during a crash. Better to write the data
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* until we are actually told to delete the file.)
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*/
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smgrcreate(smgr, forknum, true);
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lastblock = smgrnblocks(smgr, forknum);
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if (blkno < lastblock)
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{
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/* page exists in file */
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buffer = ReadBufferWithoutRelcache(rnode, forknum, blkno,
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mode, NULL);
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}
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else
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{
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/* hm, page doesn't exist in file */
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if (mode == RBM_NORMAL)
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{
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log_invalid_page(rnode, forknum, blkno, false);
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return InvalidBuffer;
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}
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if (mode == RBM_NORMAL_NO_LOG)
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return InvalidBuffer;
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/* OK to extend the file */
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/* we do this in recovery only - no rel-extension lock needed */
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Assert(InRecovery);
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buffer = InvalidBuffer;
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do
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{
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if (buffer != InvalidBuffer)
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{
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if (mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK)
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LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
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ReleaseBuffer(buffer);
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}
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buffer = ReadBufferWithoutRelcache(rnode, forknum,
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P_NEW, mode, NULL);
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}
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while (BufferGetBlockNumber(buffer) < blkno);
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/* Handle the corner case that P_NEW returns non-consecutive pages */
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if (BufferGetBlockNumber(buffer) != blkno)
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{
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if (mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK)
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LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
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ReleaseBuffer(buffer);
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buffer = ReadBufferWithoutRelcache(rnode, forknum, blkno,
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mode, NULL);
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}
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}
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|
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if (mode == RBM_NORMAL)
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{
|
|
/* check that page has been initialized */
|
|
Page page = (Page) BufferGetPage(buffer);
|
|
|
|
/*
|
|
* We assume that PageIsNew is safe without a lock. During recovery,
|
|
* there should be no other backends that could modify the buffer at
|
|
* the same time.
|
|
*/
|
|
if (PageIsNew(page))
|
|
{
|
|
ReleaseBuffer(buffer);
|
|
log_invalid_page(rnode, forknum, blkno, true);
|
|
return InvalidBuffer;
|
|
}
|
|
}
|
|
|
|
return buffer;
|
|
}
|
|
|
|
/*
|
|
* Struct actually returned by XLogFakeRelcacheEntry, though the declared
|
|
* return type is Relation.
|
|
*/
|
|
typedef struct
|
|
{
|
|
RelationData reldata; /* Note: this must be first */
|
|
FormData_pg_class pgc;
|
|
} FakeRelCacheEntryData;
|
|
|
|
typedef FakeRelCacheEntryData *FakeRelCacheEntry;
|
|
|
|
/*
|
|
* Create a fake relation cache entry for a physical relation
|
|
*
|
|
* It's often convenient to use the same functions in XLOG replay as in the
|
|
* main codepath, but those functions typically work with a relcache entry.
|
|
* We don't have a working relation cache during XLOG replay, but this
|
|
* function can be used to create a fake relcache entry instead. Only the
|
|
* fields related to physical storage, like rd_rel, are initialized, so the
|
|
* fake entry is only usable in low-level operations like ReadBuffer().
|
|
*
|
|
* Caller must free the returned entry with FreeFakeRelcacheEntry().
|
|
*/
|
|
Relation
|
|
CreateFakeRelcacheEntry(RelFileNode rnode)
|
|
{
|
|
FakeRelCacheEntry fakeentry;
|
|
Relation rel;
|
|
|
|
Assert(InRecovery);
|
|
|
|
/* Allocate the Relation struct and all related space in one block. */
|
|
fakeentry = palloc0(sizeof(FakeRelCacheEntryData));
|
|
rel = (Relation) fakeentry;
|
|
|
|
rel->rd_rel = &fakeentry->pgc;
|
|
rel->rd_node = rnode;
|
|
/* We will never be working with temp rels during recovery */
|
|
rel->rd_backend = InvalidBackendId;
|
|
|
|
/* It must be a permanent table if we're in recovery. */
|
|
rel->rd_rel->relpersistence = RELPERSISTENCE_PERMANENT;
|
|
|
|
/* We don't know the name of the relation; use relfilenode instead */
|
|
sprintf(RelationGetRelationName(rel), "%u", rnode.relNode);
|
|
|
|
/*
|
|
* We set up the lockRelId in case anything tries to lock the dummy
|
|
* relation. Note that this is fairly bogus since relNode may be
|
|
* different from the relation's OID. It shouldn't really matter though,
|
|
* since we are presumably running by ourselves and can't have any lock
|
|
* conflicts ...
|
|
*/
|
|
rel->rd_lockInfo.lockRelId.dbId = rnode.dbNode;
|
|
rel->rd_lockInfo.lockRelId.relId = rnode.relNode;
|
|
|
|
rel->rd_smgr = NULL;
|
|
|
|
return rel;
|
|
}
|
|
|
|
/*
|
|
* Free a fake relation cache entry.
|
|
*/
|
|
void
|
|
FreeFakeRelcacheEntry(Relation fakerel)
|
|
{
|
|
/* make sure the fakerel is not referenced by the SmgrRelation anymore */
|
|
if (fakerel->rd_smgr != NULL)
|
|
smgrclearowner(&fakerel->rd_smgr, fakerel->rd_smgr);
|
|
pfree(fakerel);
|
|
}
|
|
|
|
/*
|
|
* Drop a relation during XLOG replay
|
|
*
|
|
* This is called when the relation is about to be deleted; we need to remove
|
|
* any open "invalid-page" records for the relation.
|
|
*/
|
|
void
|
|
XLogDropRelation(RelFileNode rnode, ForkNumber forknum)
|
|
{
|
|
forget_invalid_pages(rnode, forknum, 0);
|
|
}
|
|
|
|
/*
|
|
* Drop a whole database during XLOG replay
|
|
*
|
|
* As above, but for DROP DATABASE instead of dropping a single rel
|
|
*/
|
|
void
|
|
XLogDropDatabase(Oid dbid)
|
|
{
|
|
/*
|
|
* This is unnecessarily heavy-handed, as it will close SMgrRelation
|
|
* objects for other databases as well. DROP DATABASE occurs seldom enough
|
|
* that it's not worth introducing a variant of smgrclose for just this
|
|
* purpose. XXX: Or should we rather leave the smgr entries dangling?
|
|
*/
|
|
smgrcloseall();
|
|
|
|
forget_invalid_pages_db(dbid);
|
|
}
|
|
|
|
/*
|
|
* Truncate a relation during XLOG replay
|
|
*
|
|
* We need to clean up any open "invalid-page" records for the dropped pages.
|
|
*/
|
|
void
|
|
XLogTruncateRelation(RelFileNode rnode, ForkNumber forkNum,
|
|
BlockNumber nblocks)
|
|
{
|
|
forget_invalid_pages(rnode, forkNum, nblocks);
|
|
}
|
|
|
|
/*
|
|
* Read 'count' bytes from WAL into 'buf', starting at location 'startptr'
|
|
* in timeline 'tli'.
|
|
*
|
|
* Will open, and keep open, one WAL segment stored in the static file
|
|
* descriptor 'sendFile'. This means if XLogRead is used once, there will
|
|
* always be one descriptor left open until the process ends, but never
|
|
* more than one.
|
|
*
|
|
* XXX This is very similar to pg_waldump's XLogDumpXLogRead and to XLogRead
|
|
* in walsender.c but for small differences (such as lack of elog() in
|
|
* frontend). Probably these should be merged at some point.
|
|
*/
|
|
static void
|
|
XLogRead(char *buf, TimeLineID tli, XLogRecPtr startptr, Size count)
|
|
{
|
|
char *p;
|
|
XLogRecPtr recptr;
|
|
Size nbytes;
|
|
|
|
/* state maintained across calls */
|
|
static int sendFile = -1;
|
|
static XLogSegNo sendSegNo = 0;
|
|
static TimeLineID sendTLI = 0;
|
|
static uint32 sendOff = 0;
|
|
|
|
p = buf;
|
|
recptr = startptr;
|
|
nbytes = count;
|
|
|
|
while (nbytes > 0)
|
|
{
|
|
uint32 startoff;
|
|
int segbytes;
|
|
int readbytes;
|
|
|
|
startoff = recptr % XLogSegSize;
|
|
|
|
/* Do we need to switch to a different xlog segment? */
|
|
if (sendFile < 0 || !XLByteInSeg(recptr, sendSegNo) ||
|
|
sendTLI != tli)
|
|
{
|
|
char path[MAXPGPATH];
|
|
|
|
if (sendFile >= 0)
|
|
close(sendFile);
|
|
|
|
XLByteToSeg(recptr, sendSegNo);
|
|
|
|
XLogFilePath(path, tli, sendSegNo);
|
|
|
|
sendFile = BasicOpenFile(path, O_RDONLY | PG_BINARY, 0);
|
|
|
|
if (sendFile < 0)
|
|
{
|
|
if (errno == ENOENT)
|
|
ereport(ERROR,
|
|
(errcode_for_file_access(),
|
|
errmsg("requested WAL segment %s has already been removed",
|
|
path)));
|
|
else
|
|
ereport(ERROR,
|
|
(errcode_for_file_access(),
|
|
errmsg("could not open file \"%s\": %m",
|
|
path)));
|
|
}
|
|
sendOff = 0;
|
|
sendTLI = tli;
|
|
}
|
|
|
|
/* Need to seek in the file? */
|
|
if (sendOff != startoff)
|
|
{
|
|
if (lseek(sendFile, (off_t) startoff, SEEK_SET) < 0)
|
|
{
|
|
char path[MAXPGPATH];
|
|
|
|
XLogFilePath(path, tli, sendSegNo);
|
|
|
|
ereport(ERROR,
|
|
(errcode_for_file_access(),
|
|
errmsg("could not seek in log segment %s to offset %u: %m",
|
|
path, startoff)));
|
|
}
|
|
sendOff = startoff;
|
|
}
|
|
|
|
/* How many bytes are within this segment? */
|
|
if (nbytes > (XLogSegSize - startoff))
|
|
segbytes = XLogSegSize - startoff;
|
|
else
|
|
segbytes = nbytes;
|
|
|
|
pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
|
|
readbytes = read(sendFile, p, segbytes);
|
|
pgstat_report_wait_end();
|
|
if (readbytes <= 0)
|
|
{
|
|
char path[MAXPGPATH];
|
|
|
|
XLogFilePath(path, tli, sendSegNo);
|
|
|
|
ereport(ERROR,
|
|
(errcode_for_file_access(),
|
|
errmsg("could not read from log segment %s, offset %u, length %lu: %m",
|
|
path, sendOff, (unsigned long) segbytes)));
|
|
}
|
|
|
|
/* Update state for read */
|
|
recptr += readbytes;
|
|
|
|
sendOff += readbytes;
|
|
nbytes -= readbytes;
|
|
p += readbytes;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Determine which timeline to read an xlog page from and set the
|
|
* XLogReaderState's currTLI to that timeline ID.
|
|
*
|
|
* We care about timelines in xlogreader when we might be reading xlog
|
|
* generated prior to a promotion, either if we're currently a standby in
|
|
* recovery or if we're a promoted master reading xlogs generated by the old
|
|
* master before our promotion.
|
|
*
|
|
* wantPage must be set to the start address of the page to read and
|
|
* wantLength to the amount of the page that will be read, up to
|
|
* XLOG_BLCKSZ. If the amount to be read isn't known, pass XLOG_BLCKSZ.
|
|
*
|
|
* We switch to an xlog segment from the new timeline eagerly when on a
|
|
* historical timeline, as soon as we reach the start of the xlog segment
|
|
* containing the timeline switch. The server copied the segment to the new
|
|
* timeline so all the data up to the switch point is the same, but there's no
|
|
* guarantee the old segment will still exist. It may have been deleted or
|
|
* renamed with a .partial suffix so we can't necessarily keep reading from
|
|
* the old TLI even though tliSwitchPoint says it's OK.
|
|
*
|
|
* We can't just check the timeline when we read a page on a different segment
|
|
* to the last page. We could've received a timeline switch from a cascading
|
|
* upstream, so the current segment ends abruptly (possibly getting renamed to
|
|
* .partial) and we have to switch to a new one. Even in the middle of reading
|
|
* a page we could have to dump the cached page and switch to a new TLI.
|
|
*
|
|
* Because of this, callers MAY NOT assume that currTLI is the timeline that
|
|
* will be in a page's xlp_tli; the page may begin on an older timeline or we
|
|
* might be reading from historical timeline data on a segment that's been
|
|
* copied to a new timeline.
|
|
*
|
|
* The caller must also make sure it doesn't read past the current replay
|
|
* position (using GetWalRcvWriteRecPtr) if executing in recovery, so it
|
|
* doesn't fail to notice that the current timeline became historical. The
|
|
* caller must also update ThisTimeLineID with the result of
|
|
* GetWalRcvWriteRecPtr and must check RecoveryInProgress().
|
|
*/
|
|
void
|
|
XLogReadDetermineTimeline(XLogReaderState *state, XLogRecPtr wantPage, uint32 wantLength)
|
|
{
|
|
const XLogRecPtr lastReadPage = state->readSegNo * XLogSegSize + state->readOff;
|
|
|
|
Assert(wantPage != InvalidXLogRecPtr && wantPage % XLOG_BLCKSZ == 0);
|
|
Assert(wantLength <= XLOG_BLCKSZ);
|
|
Assert(state->readLen == 0 || state->readLen <= XLOG_BLCKSZ);
|
|
|
|
/*
|
|
* If the desired page is currently read in and valid, we have nothing to
|
|
* do.
|
|
*
|
|
* The caller should've ensured that it didn't previously advance readOff
|
|
* past the valid limit of this timeline, so it doesn't matter if the
|
|
* current TLI has since become historical.
|
|
*/
|
|
if (lastReadPage == wantPage &&
|
|
state->readLen != 0 &&
|
|
lastReadPage + state->readLen >= wantPage + Min(wantLength, XLOG_BLCKSZ - 1))
|
|
return;
|
|
|
|
/*
|
|
* If we're reading from the current timeline, it hasn't become historical
|
|
* and the page we're reading is after the last page read, we can again
|
|
* just carry on. (Seeking backwards requires a check to make sure the
|
|
* older page isn't on a prior timeline).
|
|
*
|
|
* ThisTimeLineID might've become historical since we last looked, but the
|
|
* caller is required not to read past the flush limit it saw at the time
|
|
* it looked up the timeline. There's nothing we can do about it if
|
|
* StartupXLOG() renames it to .partial concurrently.
|
|
*/
|
|
if (state->currTLI == ThisTimeLineID && wantPage >= lastReadPage)
|
|
{
|
|
Assert(state->currTLIValidUntil == InvalidXLogRecPtr);
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* If we're just reading pages from a previously validated historical
|
|
* timeline and the timeline we're reading from is valid until the end of
|
|
* the current segment we can just keep reading.
|
|
*/
|
|
if (state->currTLIValidUntil != InvalidXLogRecPtr &&
|
|
state->currTLI != ThisTimeLineID &&
|
|
state->currTLI != 0 &&
|
|
(wantPage + wantLength) / XLogSegSize < state->currTLIValidUntil / XLogSegSize)
|
|
return;
|
|
|
|
/*
|
|
* If we reach this point we're either looking up a page for random
|
|
* access, the current timeline just became historical, or we're reading
|
|
* from a new segment containing a timeline switch. In all cases we need
|
|
* to determine the newest timeline on the segment.
|
|
*
|
|
* If it's the current timeline we can just keep reading from here unless
|
|
* we detect a timeline switch that makes the current timeline historical.
|
|
* If it's a historical timeline we can read all the segment on the newest
|
|
* timeline because it contains all the old timelines' data too. So only
|
|
* one switch check is required.
|
|
*/
|
|
{
|
|
/*
|
|
* We need to re-read the timeline history in case it's been changed
|
|
* by a promotion or replay from a cascaded replica.
|
|
*/
|
|
List *timelineHistory = readTimeLineHistory(ThisTimeLineID);
|
|
|
|
XLogRecPtr endOfSegment = (((wantPage / XLogSegSize) + 1) * XLogSegSize) - 1;
|
|
|
|
Assert(wantPage / XLogSegSize == endOfSegment / XLogSegSize);
|
|
|
|
/*
|
|
* Find the timeline of the last LSN on the segment containing
|
|
* wantPage.
|
|
*/
|
|
state->currTLI = tliOfPointInHistory(endOfSegment, timelineHistory);
|
|
state->currTLIValidUntil = tliSwitchPoint(state->currTLI, timelineHistory,
|
|
&state->nextTLI);
|
|
|
|
Assert(state->currTLIValidUntil == InvalidXLogRecPtr ||
|
|
wantPage + wantLength < state->currTLIValidUntil);
|
|
|
|
list_free_deep(timelineHistory);
|
|
|
|
elog(DEBUG3, "switched to timeline %u valid until %X/%X",
|
|
state->currTLI,
|
|
(uint32) (state->currTLIValidUntil >> 32),
|
|
(uint32) (state->currTLIValidUntil));
|
|
}
|
|
}
|
|
|
|
/*
|
|
* read_page 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.
|
|
*
|
|
* TODO: The walsender has its own version of this, but it relies on the
|
|
* walsender's latch being set whenever WAL is flushed. No such infrastructure
|
|
* exists for normal backends, so we have to do a check/sleep/repeat style of
|
|
* loop for now.
|
|
*/
|
|
int
|
|
read_local_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr,
|
|
int reqLen, XLogRecPtr targetRecPtr, char *cur_page,
|
|
TimeLineID *pageTLI)
|
|
{
|
|
XLogRecPtr read_upto,
|
|
loc;
|
|
int count;
|
|
|
|
loc = targetPagePtr + reqLen;
|
|
|
|
/* Loop waiting for xlog to be available if necessary */
|
|
while (1)
|
|
{
|
|
/*
|
|
* Determine the limit of xlog we can currently read to, and what the
|
|
* most recent timeline is.
|
|
*
|
|
* RecoveryInProgress() will update ThisTimeLineID when it first
|
|
* notices recovery finishes, so we only have to maintain it for the
|
|
* local process until recovery ends.
|
|
*/
|
|
if (!RecoveryInProgress())
|
|
read_upto = GetFlushRecPtr();
|
|
else
|
|
read_upto = GetXLogReplayRecPtr(&ThisTimeLineID);
|
|
|
|
*pageTLI = ThisTimeLineID;
|
|
|
|
/*
|
|
* Check which timeline to get the record from.
|
|
*
|
|
* We have to do it each time through the loop because if we're in
|
|
* recovery as a cascading standby, the current timeline might've
|
|
* become historical. We can't rely on RecoveryInProgress() because in
|
|
* a standby configuration like
|
|
*
|
|
* A => B => C
|
|
*
|
|
* if we're a logical decoding session on C, and B gets promoted, our
|
|
* timeline will change while we remain in recovery.
|
|
*
|
|
* We can't just keep reading from the old timeline as the last WAL
|
|
* archive in the timeline will get renamed to .partial by
|
|
* StartupXLOG().
|
|
*
|
|
* If that happens after our caller updated ThisTimeLineID but before
|
|
* we actually read the xlog page, we might still try to read from the
|
|
* old (now renamed) segment and fail. There's not much we can do
|
|
* about this, but it can only happen when we're a leaf of a cascading
|
|
* standby whose master gets promoted while we're decoding, so a
|
|
* one-off ERROR isn't too bad.
|
|
*/
|
|
XLogReadDetermineTimeline(state, targetPagePtr, reqLen);
|
|
|
|
if (state->currTLI == ThisTimeLineID)
|
|
{
|
|
|
|
if (loc <= read_upto)
|
|
break;
|
|
|
|
CHECK_FOR_INTERRUPTS();
|
|
pg_usleep(1000L);
|
|
}
|
|
else
|
|
{
|
|
/*
|
|
* We're on a historical timeline, so limit reading to the switch
|
|
* point where we moved to the next timeline.
|
|
*
|
|
* We don't need to GetFlushRecPtr or GetXLogReplayRecPtr. We know
|
|
* about the new timeline, so we must've received past the end of
|
|
* it.
|
|
*/
|
|
read_upto = state->currTLIValidUntil;
|
|
|
|
/*
|
|
* Setting pageTLI to our wanted record's TLI is slightly wrong;
|
|
* the page might begin on an older timeline if it contains a
|
|
* timeline switch, since its xlog segment will have been copied
|
|
* from the prior timeline. This is pretty harmless though, as
|
|
* nothing cares so long as the timeline doesn't go backwards. We
|
|
* should read the page header instead; FIXME someday.
|
|
*/
|
|
*pageTLI = state->currTLI;
|
|
|
|
/* No need to wait on a historical timeline */
|
|
break;
|
|
}
|
|
}
|
|
|
|
if (targetPagePtr + XLOG_BLCKSZ <= read_upto)
|
|
{
|
|
/*
|
|
* more than one block available; read only that block, have caller
|
|
* come back if they need more.
|
|
*/
|
|
count = XLOG_BLCKSZ;
|
|
}
|
|
else if (targetPagePtr + reqLen > read_upto)
|
|
{
|
|
/* not enough data there */
|
|
return -1;
|
|
}
|
|
else
|
|
{
|
|
/* enough bytes available to satisfy the request */
|
|
count = read_upto - targetPagePtr;
|
|
}
|
|
|
|
/*
|
|
* Even though we just determined how much of the page can be validly read
|
|
* as 'count', read the whole page anyway. It's guaranteed to be
|
|
* zero-padded up to the page boundary if it's incomplete.
|
|
*/
|
|
XLogRead(cur_page, *pageTLI, targetPagePtr, XLOG_BLCKSZ);
|
|
|
|
/* number of valid bytes in the buffer */
|
|
return count;
|
|
}
|