From 285bd0ac4a7c0538d544c40aa725682e11cb71a9 Mon Sep 17 00:00:00 2001 From: Michael Paquier Date: Mon, 19 Nov 2018 10:25:48 +0900 Subject: [PATCH] Remove unnecessary memcpy when reading WAL record fitting on page When reading a WAL record, its contents are copied into an intermediate buffer. However, doing so is not necessary if the record fits fully into the current page, saving one memcpy for each such record. The allocation handling of the intermediate buffer is also now done only when a record crosses a page boundary, shaving some extra cycles when reading a WAL record. Author: Andrey Lepikhov Reviewed-by: Kyotaro Horiguchi, Heikki Linnakangas Discussion: https://postgr.es/m/c2ea54dd-a1d3-80eb-ddbf-7e6f258e615e@postgrespro.ru --- src/backend/access/transam/xlog.c | 3 --- src/backend/access/transam/xlogreader.c | 27 ++++++++++++------------- 2 files changed, 13 insertions(+), 17 deletions(-) diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index 7eed5866d2..2875fe023a 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -4203,9 +4203,6 @@ CleanupBackupHistory(void) * If no valid record is available, returns NULL, or fails if emode is PANIC. * (emode must be either PANIC, LOG). In standby mode, retries until a valid * record is available. - * - * The record is copied into readRecordBuf, so that on successful return, - * the returned record pointer always points there. */ static XLogRecord * ReadRecord(XLogReaderState *xlogreader, XLogRecPtr RecPtr, int emode, diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c index 0768ca7822..c5e019bf77 100644 --- a/src/backend/access/transam/xlogreader.c +++ b/src/backend/access/transam/xlogreader.c @@ -353,19 +353,6 @@ XLogReadRecord(XLogReaderState *state, XLogRecPtr RecPtr, char **errormsg) gotheader = false; } - /* - * Enlarge readRecordBuf as needed. - */ - if (total_len > state->readRecordBufSize && - !allocate_recordbuf(state, total_len)) - { - /* We treat this as a "bogus data" condition */ - report_invalid_record(state, "record length %u at %X/%X too long", - total_len, - (uint32) (RecPtr >> 32), (uint32) RecPtr); - goto err; - } - len = XLOG_BLCKSZ - RecPtr % XLOG_BLCKSZ; if (total_len > len) { @@ -375,6 +362,19 @@ XLogReadRecord(XLogReaderState *state, XLogRecPtr RecPtr, char **errormsg) char *buffer; uint32 gotlen; + /* + * Enlarge readRecordBuf as needed. + */ + if (total_len > state->readRecordBufSize && + !allocate_recordbuf(state, total_len)) + { + /* We treat this as a "bogus data" condition */ + report_invalid_record(state, "record length %u at %X/%X too long", + total_len, + (uint32) (RecPtr >> 32), (uint32) RecPtr); + goto err; + } + /* Copy the first fragment of the record from the first page. */ memcpy(state->readRecordBuf, state->readBuf + RecPtr % XLOG_BLCKSZ, len); @@ -479,7 +479,6 @@ XLogReadRecord(XLogReaderState *state, XLogRecPtr RecPtr, char **errormsg) state->EndRecPtr = RecPtr + MAXALIGN(total_len); state->ReadRecPtr = RecPtr; - memcpy(state->readRecordBuf, record, total_len); } /* -- 2.40.0